JP5142371B2 - Ultraviolet nitride semiconductor light emitting device and manufacturing method thereof - Google Patents

Description

  The present invention relates to an ultraviolet nitride semiconductor light emitting device and a method for manufacturing the same, and more particularly to an ultraviolet nitride semiconductor light emitting device having a low threshold current density for generating laser light having a deep ultraviolet wavelength and a method for manufacturing the same.

 Short wavelength light having a wavelength of 300 nm or less is used as an essential light source in a wide range of fields such as illumination, sterilization / water purification, medical field, biochemical industry and the like. In particular, a deep ultraviolet laser is a coherent light source having a short wavelength, and thus is used as a light source for lithography in a semiconductor manufacturing process. Usually, an excimer lamp or a laser is used as a lithography light source. However, since a large number of optical components are used in the lithography apparatus, the entire apparatus becomes large.

 In addition, a method is also used in which infrared light having a wavelength of 1064 nm oscillated from a neodymium (Nd) -doped YAG laser is used to generate a fourth harmonic (266 nm) through a nonlinear optical crystal to obtain deep ultraviolet laser light. It is as low as 0.1% or less, and it is impossible to reduce power consumption. If this can be replaced with a deep ultraviolet semiconductor laser diode (LD), the device can be miniaturized. Moreover, if the light emission efficiency of about 50% realized in a commercially available blue light emitting diode (LED) can be obtained, power consumption can be reduced.

Up to now, as a material for obtaining short wavelength light having a wavelength of 300 nm or less, aluminum gallium nitride (Al _X ) having an aluminum nitride (AlN) molar fraction x of 0.3 or more epitaxially grown on a c-plane sapphire substrate. Ga _1-X N) mixed crystals and their quantum wells (QW) are exclusively used. For example, an AlGaN / AlGaN multi-quantum well (MQW) light emitting diode (LED) approaching a wavelength of 250 nm is disclosed (see, for example, Non-Patent Document 1).

However, the AlGaN epitaxial growth layer on the sapphire substrate contains threading dislocations having a density that is about two to three orders of magnitude higher than threading dislocations (density: about 10 ⁸ cm ⁻² ) included in commercially available blue LEDs. In addition, the fact that the nitride semiconductor crystal does not have inversion symmetry along the c-axis, “spontaneous polarization” caused by the different sizes of group III atoms and nitrogen atoms, and the lattice constants of the well layer and the barrier layer Due to the “piezoelectric polarization” caused by the difference, a strong internal electric field exceeding 1 MV / cm is generated in the well due to the heterointerface charge generated in a sheet shape in the c-plane. For this reason, the luminous efficiency is less than 0.1%.

 Although there are reports on stimulated emission by photoexcitation for the development of LDs in the same wavelength region, many problems remain, such as reduction of dislocations / defect density, optimization of p-type layers, and selection of light guiding direction. There is no prospect of conversion (for example, see Non-Patent Document 2).

In particular, gallium nitride (GaN) and AlN have different band ordering in the valence band (arrangement order of energies of bands having a certain symmetry), so that the Al _x Ga _1-x N mixed crystal increases as the AlN molar fraction x increases. Is changed from a direction perpendicular to the c-axis to a direction parallel to the c-axis. For this reason, an Al _x Ga _1-x N-based LD requires a different structure from a commercially available indium gallium nitride (InGaN) -based LD in order to guide light efficiently.

 Up to now, InGaN / GaN MQW that has been grown on nonpolar planes (a-plane, m-plane) or semipolar plane as a technology for reducing the internal electric field has been used for the active layer of LEDs and LDs, An m-plane LED having an efficiency (38.9%) approaching the external quantum efficiency (about 50%) has been reported (for example, see Non-Patent Document 3). A blue-violet m-plane LD having a wavelength of 400 nm that continuously oscillates at room temperature has also been reported (see, for example, Non-Patent Document 4).

 Conventional ultraviolet light (wavelength of about 300 nm or less) light-emitting LD is composed of a crystal growth surface on the c-axis (polar plane) surface of a GaN crystal (hexagonal system) or slightly inclined from the c-axis (for example, Patent Literature 1). For this reason, the internal electric field effect resulting from the piezoelectric polarization generated by strain cannot be sufficiently reduced. In addition, the polarization characteristic of ultraviolet rays has a problem that the electric field vector E and the c-axis are perpendicular to each other, and the luminous efficiency is low.

 Further, in an LED formed by laminating at least an n-type nitride semiconductor layer, a light emitting layer, and a p-type nitride semiconductor layer on a c-axis oriented substrate, the Al mole fraction is 30% with an AlGaN mixed crystal having an MQW structure. The following to 60% or more have already been disclosed (for example, see Patent Document 2).

 However, an AlGaN mixed crystal having an MQW structure having an Al mole fraction in the range of 30% to 60% has not yet been disclosed.

In addition, as disclosed in Patent Document 1, there is an example in which it is inclined near the c axis or the c axis, but the axis direction of the active layer is greatly inclined from the c axis, for example, 40 ° to 90 °. The technology in the ultraviolet region is not yet disclosed.
JP 2007-201019 A JP 2007-165405 A By M. Asif Khan, M. Shatalov, M. Asif Khan, M. Shatalov, HP Maruska, HM Wang, and E. Kuokstis, “Japanese Journal of Applied. Physics (Jpn. J. Appl. Phys.), 44, 7191 (2005) For example, T. Takano, W. Narita, A. Horiuchi, and H. Kawanishi, “Applied Physics Letters (Appl. Phys. Lett.), 84, 3567 (2004). MC Schmidt, Kay Sea Kim, H Sato, N Fellows, H Masui, S Nakamura, SP Denver, and MC Smidt, K.-C. Kim , H. Sato, N. Fellows, H. Masui, S. Nakamura, SP DenBaars, and JS Speck), “Japanese Journal of Applied Physics”, 46th. Volume 126 (2007) "Japanese Journal," by K. Okamoto, H. Ohta, S. F. Chichibu, J. Ichihara, and H. Ohta, SF Chichibu, J. Ichihara, and H. Takasu Of Applied Physics (Jpn. J. Appl. Phys.), 46, 187 (2007)

 For light emission from the strained m-plane InGaN / GaN MQW, the electric field component E mainly exhibits a polarization direction parallel to the a-axis, so the resonator mirror surface must be formed along the c-plane. The c-plane is not cleaved better than the a-plane, which causes a decrease in yield.

 An object of the present invention is to provide an ultraviolet nitride semiconductor light emitting device having a low threshold current density in order to solve the problems such as an increase in size and low efficiency of a deep ultraviolet laser.

 The object of the present invention is to determine the AlGaN mixed fractions of AlGaN crystals grown on a hexagonal nonpolar plane (a-plane, m-plane) or semipolar plane and the Al and Ga molar fractions used in the active layer. To provide an ultraviolet nitride semiconductor light emitting device capable of improving the light emission efficiency, realizing a low threshold current density, and generating a laser beam having a deep ultraviolet wavelength by an optimized quantum well structure, and a method for manufacturing the same. is there.

According to one aspect of the present invention for achieving the above object , any one of a nonpolar plane substrate and a semipolar plane substrate and the substrate is disposed on the substrate and doped with an n-type impurity. A quantum well structure comprising an AlGaN layer, an Al _x Ga _1-x N (0 ≦ x ≦ 1) barrier layer and an Al _x Ga _1-x N (0 ≦ x ≦ 1) well layer disposed on the AlGaN layer Al _x Ga _1-x N / Al _x Ga _1-x N active layer having the above and Al _x Ga _1-x N / Al _x Ga _1-x N active layer, doped with p-type impurities A plane in which the c-axis is inclined within the range of 40 ° to 90 ° from the normal direction of the main surface of crystal growth, and the electric field component E of light is mainly the c-axis. shows the polarization characteristics made parallel (E // c) and the end face of the laser resonator formed on the crystal growth surface in the crystal grown above the active layer is in a plane Made is, ultraviolet nitride semiconductor light emitting element according to 3 below the number of wells of the active layer.

 The main surface of the crystal growth includes a nonpolar surface or a semipolar surface.

  The nonpolar plane includes an m-plane or an a-plane.

  The semipolar plane includes any one of {10-11} plane, {10-12} plane, or {11-22} plane.

 When any one of the m-plane, {10-11} plane, or {10-12} plane is selected as the principal plane for crystal growth, the a-plane is used as the reflecting mirror of the laser resonator.

 The a-plane is a cleavage plane.

The active layer has a single well or multiple quantum well structure, and the Al _X Ga _1-X N well layer has an AlN molar fraction of 30% to 60%, and the Al _X Ga _1-X The ratio of the AlN mole fraction of the N barrier layer to the AlN mole fraction of the Al _x Ga _1-x N well layer is 0.7 or more.

According to another aspect of the present invention, an m-plane substrate, an AlInN layer disposed on the m-plane substrate and doped with an n-type impurity, and an Al _1-x In _x N disposed on the AlInN layer. An Al _{1 -X} In _X N / Al _{1 -X} In _X N active layer having a quantum well structure including a barrier layer and an Al _{1 -X} In _X N well layer, and the Al _{1 -X} In _X N / Al _1- An AlInN layer disposed on an _X In _X N active layer and doped with a p-type impurity, and having a c-axis inclined within a range of 40 ° to 90 ° from a normal direction of a main surface of crystal growth the principal surface of the crystal growth, the electric field component of light E is shows a polarizing characteristic mainly made parallel to the c axis (E // c), the laser resonator formed in the active layer was grown by the crystal growth surface An ultraviolet nitride semiconductor light-emitting device is provided in which the end face of the vessel is formed as a-plane and the number of wells in the active layer is 3 or less .

 The active layer has a single well or multiple quantum well structure and has an InN molar fraction of 5% or less.

According to another aspect of the present invention, a step of preparing an m-plane substrate, and a surface on which the c-axis is inclined within a range of 40 ° to 90 ° from the normal direction of the main surface of crystal growth And a step of forming an AlGaN layer doped with an n-type impurity on the m-plane substrate, and a quantum comprising an Al _x Ga _1-x N barrier layer and an Al _x Ga _1-x N well layer on the AlGaN layer. forming a _{Al X Ga 1-X N /} Al X Ga 1-X N active layer so as to have a well structure to the number of wells of the active layer 3 below, the Al _X Ga _1-X N Nitride semiconductor light emitting process comprising: forming an AlGaN layer doped with a p-type impurity on an Al / Ga _x Ga _1-x N active layer; and forming a reflecting surface of the laser resonator along the a-plane An element manufacturing method is provided.

 The step of forming the reflection surface of the laser resonator along the a-plane has a cleavage.

 The n-type impurity is Si, and the p-type impurity is Mg.

 According to the present invention, the AlGaN mixed crystal grown on a hexagonal nonpolar plane (a-plane, m-plane) or semipolar plane, and the Al and Ga mole fractions of the AlGaN crystal used in the active layer are obtained. With the optimized quantum well structure, it is possible to provide an ultraviolet nitride semiconductor light emitting device and a method for manufacturing the same, which can improve the light emission efficiency and generate laser light having a deep ultraviolet wavelength with a low threshold current density.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic and different from the actual ones. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

 Further, the embodiment described below exemplifies an apparatus and a method for embodying the technical idea of the present invention. The technical idea of the present invention is the arrangement of each component as described below. It is not something specific. The technical idea of the present invention can be variously modified within the scope of the claims.

[First embodiment]
FIG. 1 is a comparison of band diagrams of a GaN layer and an AlN layer applied to the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention. FIG. A band diagram, FIG. 1 (b), shows a band diagram at the Γ point of AlN.

Group III nitride semiconductors have a hexagonal wurtzite structure as a stable phase. For this reason, the valence band causes crystal field splitting (Δcr) in addition to spin-orbit splitting (Δso). As a result, the valence band of unstrained GaN has symmetry of Γ _9V , Γ ^u _7V , Γ ^l _7V in order from the higher energy side, as shown in FIG.

Transitions from the respective bands to the conduction band (Γ _7C ) are called A transition, B transition, and C transition in this order, and the A and B transitions are perpendicular to the electric field vector E of light and the c axis that is the optical axis of the crystal ( When E⊥c), the C transition is mainly allowed when E and c-axis are parallel (E // c).

On the other hand, in the unstrained AlN, since the crystal field splitting Δcr is negative, the band ordering is Γ ^u _7V , Γ _9V , Γ ^l _{7V in} order from the higher energy side as shown in FIG. In this case, the A transition is mainly permitted when the electric field vector E and the c-axis are parallel (E // c), and the B and C transitions are mainly permitted when the electric field vector E and the c-axis are vertical (E⊥c).

 So far, there have been many reports on optical properties near the band edge of GaN. For example, strain dependence of exciton transition energy and experimental values of band parameters such as Δso and Δcr have been reported (S Chichibu, A. Shikanai, T. Azuhata, T. Sota, A. Kuramata, K. Horino, and S. Nakamura, Appl. Phys. Lett. 68, 3766 (1996), and A. Shikanai, T. Azuhata, T. Sota, S. Chichibu, A. Kuramata, K. Horino, and S. Nakamura, J. Appl. Phys. 81, 417 (1996)). On the other hand, no similar report has been made for AlN.

The present inventors collected strain dependence of exciton transition energy in AlN grown on a c-plane sapphire substrate as experimental data, and quantified the band parameters of AlN for the first time from their theoretical fitting. Based on this, the band parameters of the Al _x Ga _1-x N mixed crystal are derived by linear interpolation of the data of GaN and AlN, and the dependence of the band ordering of the valence band on the AlN mole fraction x is obtained. It was.

Figure 2 is a characteristic of the Al _X Ga _1-X N mixed crystal is applied to a UV nitride semiconductor light emitting device according to a first embodiment of the present invention, FIG. 2 (a), unstrained Al _X FIG. 2 (b) shows the dependence of the band ordering on the top of the valence band of Ga _1-X N mixed crystal depending on the AlN molar fraction x. FIG. 2 (b) shows the Al _X Ga _{1− The} dependence of the strain ε _zz (%) in the c-axis direction of the _XN mixed crystal on the AlN mole fraction x is shown.

In FIG. 2, E ₁ , E ₂ and E ₃ represent transition energies from the top of the valence band to the conduction band. In the case of GaN, E ₁ , E ₂ , and E ₃ correspond to A, B, and C transition energies. Further, δ _a represents the coefficient of the nonlinear term of the in-plane lattice constant a of the AlGaN mixed crystal.

As shown in FIG. 2, the Al _X Ga _1-X N mixed crystal unstrained, AlN molar fraction x = 0.095, underwent tensile strain to the grown plane on GaN Al _X Ga _1-X In N mixed crystal, when x = 0.032 to 0.048 is exceeded, the band ordering is switched from Γ _9V , Γ ^u _7V , Γ ^l _7V to Γ ^u _7V , Γ _9V , Γ ^l _7V .

As is clear from FIG. 2A, at the intersection (x = 0.095) of the reference line E ₁ (Γ ₉ ) line and E ₂ (Γ ₇ ) −E ₁ (Γ ₉ ) line, Γ _9V And Γ ^u _7V are interchanged.

In FIG. 2B, the line δ _a = 0 (Å) represents the result when the nonlinear effect is not considered in the in-plane lattice constant a of the mixed crystal. Moreover, the line of δ _a = −0.04 (Å) represents the result when the nonlinear effect is considered (BT Liou, SH Yen, and YK Kuo, Appl. Phys. A 81, 1459 (2005)).

On the other hand, the E ₂ (Γ ₇ ) = E ₁ (Γ ₉ ) line represents the boundary where the band ordering at the top of the valence band is switched. The upper part of the E ₂ (Γ ₇ ) = E ₁ (Γ ₉ ) line is Γ _9V , Γ ^u _7V , Γ ^l _7V , and the lower part is Γ ^u _7V , Γ _9V , Γ ^l _7V . When x = 0.032 and x = 0.048, Γ _9V and Γ ^u _7V are interchanged.

Therefore, if the AlN molar fraction x was used 0.1 or more Al _X Ga _1-X N mixed crystal and a quantum well active layer of the LD, the light emission, the electric field vector E and the c-axis is parallel to (E // C) shows the polarization characteristics.

(Basic element structure)
FIG. 3 is a schematic diagram for explaining a nonpolar plane and a semipolar plane applied to the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention.

 FIG. 3A is a schematic diagram showing the crystal structure of a group III nitride semiconductor, and FIG. 3B illustrates the m-plane {1-100} and the a-plane {11-20} which are nonpolar planes. FIG. 3C is a schematic diagram for explaining the semipolar surface {10-11}, and FIG. 3D is a schematic diagram for explaining the semipolar surface {10-12}. FIG. 3E is a schematic diagram for explaining the semipolar plane {11-22}.

 As apparent from FIG. 3B, the m-axis direction <10-10> perpendicular to the m-plane forms an angle θ = 90 ° with respect to the c-axis direction <0001>. The a-plane {11-20} and c-axis are parallel, and the a-axis direction <11-20> perpendicular to the a-plane {11-20} forms 90 ° with respect to the c-axis direction <0001>. .

 As apparent from FIG. 3C, the <10-11> direction perpendicular to the semipolar plane {10-11} forms an angle θ = 62 ° with respect to the c-axis direction <0001>.

 As is clear from FIG. 3D, the <10-12> direction perpendicular to the semipolar plane {10-12} forms an angle θ = 43 ° with respect to the c-axis direction <0001>.

 As is clear from FIG. 3E, the <10-22> direction perpendicular to the semipolar plane {10-22} forms an angle θ = 58 ° with respect to the c-axis direction <0001>.

 FIG. 4 is a schematic bird's-eye view of the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention. At the same time, an LDW in which an AlGaN / AlGaN active layer 16 having an MQW structure is formed on an m-plane GaN substrate 10. The conceptual diagram of is shown.

As shown in FIG. 4, the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention includes an m-plane substrate 10 and an AlGaN layer disposed on the m-plane substrate 10 and doped with an n-type impurity. (12, 14) and an Al _x Ga _1- having a quantum well structure which is disposed on the AlGaN layer (12, 14) and includes an Al _x Ga _1-x N barrier layer and an Al _x Ga _1-x N well layer. _X and _{N / Al X Ga 1-X} N active layer _{16, Al X Ga 1-X} N / Al X Ga is placed on _1-X N active layer 16, AlGaN layer doped with p-type impurities (18, 20), and as shown in FIGS. 3 (b) to 3 (e), a crystal whose c-axis is inclined within a range of 40 ° to 90 ° from the normal direction of the main surface of crystal growth And an electric field component E of light mainly exhibits a polarization characteristic parallel to the c axis (E // c).

 Here, in the example of FIG. 3D, the <10-12> direction perpendicular to the semipolar plane {10-12} forms an angle θ = 43 ° with respect to the c-axis direction <0001>. When a crystal growth plane is formed, an off-angle plane of about 3 ° plus / minus is applied to ensure a desired crystal growth rate and surface morphology.

 Therefore, in the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention, the crystal growth is performed on a plane in which the c-axis is inclined within a range of 40 ° to 90 ° from the normal direction of the main surface of crystal growth. The main surface.

 In the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention, as shown in FIGS. 3B to 3E, the main surface of crystal growth is a nonpolar plane or A semipolar plane is included.

  Further, in the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention, as shown in FIG. 3B, the nonpolar surface includes an m-plane or a-plane. To do.

 Further, in the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention, as shown in FIGS. 3C to 3E, the semipolar plane has a {10-11} plane. , {10-12} plane, or {11-22} plane, any one of them is included.

 Further, in the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention, any one of the m-plane, {10-11} plane, and {10-12} plane as the main surface for crystal growth. When one plane is selected, the a plane is used as a reflector of the resonator.

 That is, as shown in FIGS. 3B to 3E, when any of the m-plane, {10-11} plane, and {10-12} plane is selected as the main plane of crystal growth. However, the end face of the laser resonator having the stripe structure shown in FIG.

 In the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention, the m-plane substrate 10 is used, and the c-axis is within the range of 40 ° to 90 ° from the normal direction of the main surface of crystal growth. When an inclined surface is used as the main surface for crystal growth, the end surface of the laser resonator having the stripe structure shown in FIG. 4 is the a-plane regardless of which surface is selected as the main surface for crystal growth.

 In the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention, the a-plane is a cleavage plane.

In the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention, the active layer has a single well or multiple quantum well structure, and the AlN mole content of the Al _x Ga ₁ -xN well layer. The ratio is 30% or more and 60% or less, and the ratio of the AlN mole fraction of the Al _X Ga _1-X N barrier layer to the AlN mole fraction of the Al _X Ga _1-X N well layer is 0.7 or more. It is characterized by being.

(Detailed element structure)
As shown in FIG. 4, the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention is disposed on an m-plane GaN substrate 10 and the m-plane GaN substrate 10 and is doped with an n-type impurity. AlGaN cladding layer 12, AlGaN waveguide layer 14 disposed on AlGaN cladding layer 12 and doped with n-type impurities, AlGaN waveguide layer 14, Al _X Ga _1-X N / Al _X Ga _{A 1-X} N active layer 16; an AlGaN waveguide layer 18 disposed on the Al _X Ga _1-X N / Al _X Ga _1-X N active layer 16 and doped with a p-type impurity; and an AlGaN waveguide layer 18 is disposed on the AlGaN cladding layer 20 doped with p-type impurities, the AlGaN contact layer 22 disposed on the AlGaN cladding layer 20 and doped with p-type impurities, and disposed on the AlGaN contact layer 22. A p-side electrode 26 that is in ohmic contact with the AlGaN contact layer 22; an n-side electrode 24 that is disposed on the m-plane GaN substrate 10 so as to face the p-side electrode 26 and is in ohmic contact with the m-plane GaN substrate 10; A surface whose axis is inclined within a range of 40 ° to 90 ° from the normal direction of the main surface of crystal growth is a main surface of crystal growth, and an electric field component E of light is mainly parallel to the c-axis (E // c) It is characterized by exhibiting the following polarization characteristics.

 The main surface of crystal growth includes a nonpolar surface or a semipolar surface.

 The nonpolar plane includes an m-plane or a-plane.

 The semipolar plane includes any one of {10-11} plane, {10-12} plane, and {11-22} plane.

 When any one of the m-plane, {10-11} plane, or {10-12} plane is selected as the principal plane for crystal growth, the a-plane is used as the reflector of the resonator.

 The a-plane is a cleavage plane.

Active layer 16 has a single well or multiple quantum well structure, Al _X Ga _1-X AlN molar fraction of N well layer is 60% or less than 30% and, Al _X Ga _1-X N barrier the ratio of the AlN molar fraction of AlN molar fraction of the layer and Al _X Ga _1-X N well layer is 0.7 or more.

 In FIG. 4, a part of the AlGaN contact layer 22 and the AlGaN cladding layer 20 is removed in a stripe shape by using an etching technique such as reactive ion etching (RIE) to form a ridge stripe structure. That is, a part of the p-type AlGaN cladding layer 20 and the p-type AlGaN contact layer 22 have a ridge structure along the a-axis by dry etching for lateral mode control. On the AlGaN contact layer 22 having such a ridge stripe structure, a p-side electrode 26 is disposed to form a separate confinement type structure.

 The p-side electrode 26 is formed in a stripe-shaped region along the a-axis, a resonator is formed along the stripe direction, and an end surface is an a-plane.

 Since the a-plane of GaN exhibits good cleavage properties, in the ultraviolet nitride semiconductor laser diode according to the first embodiment of the present invention, the reflection loss at the end face is reduced and the threshold current density is reduced. Can do.

 The LD shown in FIG. 4 uses free-standing m-plane GaN exhibiting n-type conductivity as a substrate, and an n-side electrode is formed on the back surface. When an insulating substrate such as m-plane SiC or r-plane sapphire is used, an n-type AlGaN contact layer is inserted between the m-plane substrate 10 and the n-type AlGaN cladding layer 12 to produce a mesa structure, and then an n-type The n-side electrode 24 may be formed on the AlGaN contact layer.

 In order to avoid absorption of ultraviolet light by the GaN m-plane substrate 10, a self-supporting AlN or AlGaN substrate may be used. The off-angle of the free-standing m-plane GaN substrate is, for example, within about plus / minus 1 °.

The p-type AlGaN contact layer 22 is a low resistance layer for making ohmic contact with the p-side electrode 26. The p-type AlGaN contact layer 22 can be formed by doping Mg as a p-type dopant at a high concentration (doping concentration is about 3 × 10 ¹⁹ cm ⁻³ , for example).

 The n-type AlGaN cladding layer 12 and the p-type AlGaN cladding layer 20 are layers for confining light from the AlGaN / AlGaN active layer 16.

The thickness is, for example, about 1 μm, the n-type dopant is Si (doping concentration is, for example, about 1 × 10 ¹⁸ cm ⁻³ ), and the p-type dopant is Mg (the doping concentration is, for example, about 1 × By doping 10 ¹⁹ cm ⁻³ ), the n-type AlGaN cladding layer 12 and the p-type AlGaN cladding layer 20 can be formed.

 The n-type AlGaN cladding layer 12 and the p-type AlGaN cladding layer 20 can perform good optical confinement by making the band gap energy larger than that of the AlGaN waveguide layer 14.

The n-type AlGaN waveguide layer 14 and the p-type AlGaN waveguide layer 18 are layers for confining carriers (electrons and holes) in the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16. . The thicknesses of the n-type AlGaN waveguide layer 14 and the p-type AlGaN waveguide layer 18 are, for example, about 0.1 μm, and the n-type dopant is Si (doping concentration is, for example, about 1 × 10 ¹⁸ cm ^−3. The n-type AlGaN cladding layer 12 and the p-type AlGaN cladding layer 20 can be formed by doping Mg as a p-type dopant (doping concentration is about 5 × 10 ¹⁸ cm ⁻³ , for example). it can.

The Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 includes an Al _x Ga _1-x N well layer (eg, 3 nm thick) and an Al _x Ga _1-x N barrier layer (eg, 9 nm thick). Is formed by laminating a plurality of periods. In order to reduce the volume of the active layer and reduce the threshold current density, the number of wells is set to 3 or less.

A forward bias voltage is applied between the p-side electrode 26 and the n-side electrode 24 disposed on the m-plane GaN substrate 10 so as to face the p-side electrode 26, thereby conducting a forward current. A current is injected into the / AlGaN active layer 16 to form a laser resonator in the Al _X Ga _{1 -X} N / Al _X Ga _{1 -X} N active layer 16. The end face of the laser resonator is composed of a-plane formed by cleavage, and the longitudinal direction of the laser resonator is formed along a ridge stripe shape. Thus, the Al _x Ga _1-x N / Al _x Ga _1-x between the p-side electrode 26 and the n-side electrode 24 disposed on the m-plane GaN substrate 10 so as to face the p-side electrode 26. A laser resonator formed in the N active layer 16 constitutes a gain structure.

The AlGaN clad layer 12 and the AlGaN clad layer 20 have a carrier confinement effect on the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16.

The AlGaN waveguide layer 14 and the AlGaN waveguide layer 18 have a light confinement effect on the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16.

  As shown by the solid line in FIG. 4, the laser beam emitted from the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention has an electric field vector component E that is parallel to the c-axis [0001]. The polarization characteristic of the TE mode having the polarization characteristic of / c is shown. Since the cleavage resonator LD normally guides the TE mode, the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention exhibits an efficient waveguide performance and has a threshold current density. Can be reduced. As a result, it is possible to improve the light emission efficiency and generate laser light having a deep ultraviolet wavelength at a low threshold current density.

(Comparative example)
FIG. 5 is a schematic bird's-eye view of an ultraviolet nitride semiconductor light-emitting device according to a comparative example of the present invention, and shows a conceptual diagram of an LD in which an AlGaN / AlGaN active layer 160 having an MQW structure is formed on a c-plane GaN substrate 100. . FIG. 5 corresponds to a blue-violet LD structure having a wavelength of 405 nm.

 As shown in FIG. 5, the ultraviolet nitride semiconductor light emitting device according to the comparative example of the present invention is arranged on a c-plane GaN substrate 100 and an AlGaN cladding layer 120 arranged on the c-plane GaN substrate 100 and doped with n-type impurities. An AlGaN waveguide layer 140 disposed on the AlGaN cladding layer 120 and doped with an n-type impurity; an AlGaN / AlGaN active layer 160 having an MQW configuration disposed on the AlGaN waveguide layer 140; and an AlGaN / AlGaN active layer AlGaN waveguide layer 180 disposed on layer 160 and doped with p-type impurities, AlGaN cladding layer 200 disposed on AlGaN waveguide layer 180 and doped with p-type impurities, and disposed on AlGaN cladding layer 200 And p-type impurity doped AlGaN contact layer 220 and AlGaN contact layer 220 A p-side electrode 260 disposed in ohmic contact with the AlGaN contact layer 220, and an n-side electrode 240 disposed on the c-plane GaN substrate 100 facing the p-side electrode 260 and in ohmic contact with the c-plane GaN substrate 100. .

 Also in FIG. 5, a ridge stripe structure is formed.

 A forward bias voltage is applied between the p-side electrode 260 and the n-side electrode 240 disposed on the c-plane GaN substrate 100 so as to face the p-side electrode 260, thereby conducting forward current. A current is injected into the / AlGaN active layer 160 to form a laser resonator in the AlGaN / AlGaN active layer 160. The end face of the laser resonator is an m-plane, and the longitudinal direction of the laser resonator is formed in the m-axis direction along the ridge stripe shape. As described above, the laser resonator formed in the AlGaN / AlGaN active layer 160 between the p-side electrode 260 and the n-side electrode 240 disposed on the m-plane GaN substrate 100 so as to face the p-side electrode 260. Constitutes a gain structure.

  The laser light emitted from the ultraviolet nitride semiconductor light emitting device according to the comparative example of the present invention has an E // c polarization characteristic in which the electric field vector component E is parallel to the c-axis, as indicated by the dotted line in FIG. The light emission has TM mode polarization characteristics. Usually, in the cleavage resonator LD, since the TE mode is guided, the carrier does not oscillate unless the carrier is filled up to the allowable band. Therefore, in the ultraviolet nitride semiconductor light emitting device according to the comparative example of the present invention, An increase in threshold current density is inevitable.

(Resonator mirror surface and guided mode)
FIG. 6A is a diagram showing a waveguide mode when the c-plane is used as the resonator mirror surfaces 28a and 28b, and FIG. 6B is used for the a-plane as the resonator mirror surfaces 30a and 30b. It is a figure showing the waveguide mode in the case of being. In the example of FIG. 6A, as indicated by the solid line in FIG. 6A, the light having the polarization characteristic of E⊥c in which the electric field vector component E is perpendicular to the c-axis is TE mode waveguide characteristics. Indicates. On the other hand, in the example of FIG. 6B, as indicated by the solid line in FIG. 6B, the light having the polarization characteristic of E // c in which the electric field vector component E is parallel to the c axis is TE. The wave guide characteristics of the mode are shown.

 As shown in FIG. 6B, when the resonator mirror surfaces 28a and 28b are formed of the a-plane, the light having the polarization characteristic of E // c shows the polarization characteristic of the TE mode with respect to the waveguide. Efficient optical waveguide is possible. Similarly, when the resonator mirror surfaces 28a and 28b are formed with an m-plane, light having the polarization characteristic of E // c exhibits TE-mode polarization characteristics with respect to the waveguide. It becomes possible.

 Therefore, in the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention, AlGaN / AlGaN MQW subjected to nonpolar plane (a plane, m plane) or semipolar plane growth is employed as the active layer. As a result, as shown in FIG. 6B, when the resonator mirror surfaces 30a and 30b are formed by the a-plane or the m-plane, the light having the polarization characteristic of E // c is not polarized in the TE mode with respect to the waveguide. Since the wave characteristic is shown, efficient optical waveguide is possible.

 In addition to this, as shown in FIG. 4 and FIG. 6B, since the c-axis, which is the direction in which polarization occurs, is in the quantum well plane, no fixed charges are generated at the upper and lower interfaces of the quantum well. The field effect can be reduced.

 Furthermore, since GaN is easily cleaved at the a-plane, it is advantageous from the viewpoint of improving yield to perform m-plane growth and provide a resonator with the a-plane as a reflecting mirror.

 For the above three reasons, the threshold current density can be reduced in the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention.

In FIG. 4, free-standing m-plane GaN is used as a substrate for m-plane growth, but m-plane SiC, (100) plane LiAlO _2, or the like may be used as a heterogeneous substrate. Further, r-plane sapphire or the like may be used as a substrate for a-plane growth.

 The semipolar plane means an inclined plane between the c plane and the nonpolar plane (a plane, m plane) as shown in FIGS. 3 (c) to 3 (e). When this surface is used, the c-axis is the m-axis with respect to the normal direction of the quantum well surface so that light having the polarization characteristic of E // c preferentially has the polarization characteristic of the TE mode. For example, a plane inclined in the range of about 40 ° to 90 ° in the (or a-axis) direction is selected. For example, {10-11} plane, {10-12} plane, {11-22} plane, etc.

(AlN mole fraction of Al _x Ga _1-x N well layer)
FIG. 18A shows the relationship between the oscillation wavelength of the laser beam and the AlN molar fraction x in the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention. FIG. 18B shows the relationship between the band gap energy and the AlN molar fraction x of the Al _x Ga _1-x N well layer in the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention. Show. Here, the band gap energy Eg (x) can be expressed by the following equation (T. Onuma, SF Chichibu et al., JAP 95, 2495 (2004)).

Eg (x) = 6.04x + 3.412 (1-x) −0.82x (1-x) (1)
When emitting light at a wavelength of 300 nm, the AlN molar fraction x of the Al _x Ga _1-X N well layer is 0.3, and when emitting light at a wavelength of 285 nm, the AlN molar fraction x of the Al _x Ga _1-X N well layer When the light is emitted at a wavelength of 270 nm, the AlN molar fraction x of the Al _x Ga _1-x N well layer is set to 0.5.

(AlN mole fraction of Al _x Ga _1-x N barrier layer)
These contrast, AlN molar fraction x of Al _X Ga _1-X N barrier layer, in order to avoid excessive compressive strain to Al _X Ga _1-X N well layer is designed by the following procedure.

Figure 7 is unstrained Al _X Ga _1-X N strain in the c-axis direction generated in the Al _X Ga _1-X N well layer laminated on the barrier layer epsilon _zz of _{(%), Al X Ga 1} -X The AlN mole fraction x dependence of N barrier layer is shown.

 The results are derived based on the results obtained in FIG. In FIG. 7, the intersecting straight lines represent boundaries where band ordering on the top of the valence band is switched.

In FIG. 7, the upper part of the intersecting straight lines is Γ _9V , Γ ^u _7V , Γ ^l _7V , and the lower part is Γ ^u _7V , Γ _9V , Γ ^l _7V . For example, when the Al _x Ga _1-x N well layer is x = 0.4, the Al _x Ga _1-x N barrier layer is x> 0.56 and compressive strain into the plane causes Γ ^u _7V , Γ _9V , Γ ^l _7V , band ordering is switched from Γ ^u _7V , Γ _9V , Γ ^l _7V to Γ _9V , Γ ^u _7V , Γ ^l _7V .

 For this reason, the electric field component E of light emission becomes a polarization direction parallel to the a axis, and light emission having the polarization characteristic of E // c obtained in the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention is obtained. It will not be possible.

For the above reasons, when the AlN mole fraction x of the Al _x Ga _1-x N well layer is 0.3, 0.4, 0.5, the AlN mole fraction of the Al _x Ga _1-x N barrier layer The rate is 0.41, 0.56, 0.71 or less.

 The n-side electrode 24 is made of, for example, a Ti / Al alloy, and the p-side electrode 26 is made of, for example, an Al metal or a Pd / Au alloy, and is in ohmic contact with the n-type GaN substrate 10 and the p-type AlGaN contact layer 22, respectively. The

(Number of wells in MQW)
FIG. 19 is a diagram showing the relationship between the hole density and the distance, taking an example of one structure of a GaN / InGaN blue-violet LD, and explaining the non-uniform hole distribution in the MQW active layer (K. Domen et al., MRS Internet J. Nitride Semicond. Res. 3, 2 (1988)). FIG. 20 is a diagram illustrating the relationship between the hole density and the distance, taking another structure of GaN / InGaN blue-violet LD as an example, and is a diagram illustrating the non-uniform hole distribution in the MQW active layer. (JY Chang et al., JAP 93, 4992 (2003)). FIG. 21 is a graph showing the relationship between the threshold current density J (kA / cm ² ) and the number of InGaN wells in a GaN / InGaN blue-violet LD (S. Nakamura et al., JJAP 37, L1020 (1998)).

 As shown in FIGS. 19 to 20, it can be seen that the density of holes injected into each well of the MQW active layer is not uniform. Increasing the number of MQW cycles improves the crystallinity of the uppermost quantum well, but the lower well does not sufficiently inject holes, and thus acts as a self-absorbing layer. Further, as shown in FIG. 21, when the number of MQW cycles is 2, the threshold current density is the smallest.

Also in the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention, there is an optimum number of MQW cycles. Also in the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention, the optimum number of MQW periods of the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 is 3 or less. It is. Although the crystallinity of the uppermost quantum well is improved even if the number of MQW cycles of the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 is increased, the lower well has sufficient holes. This is because, since it is not implanted, it works as a self-absorbing layer, so that 2 to 3 pairs of the extreme uppermost layer have an effective MQW cycle number.

(manufacturing device)
-MOVPE equipment-
FIG. 16 shows a schematic configuration of a MOVPE apparatus applied to the method for manufacturing the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention.

As shown in FIG. 16, the MOVPE apparatus applied to the method for manufacturing the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention is arranged in a reaction tank 60 and on the susceptor 56. The substrate 52 is provided, and a heating mechanism is provided outside the reaction vessel 60. The hydrogen (or nitrogen or both) carrier gas supply tank 40 and the aluminum (Al) supply connected to the hydrogen (or nitrogen or both) carrier gas supply tank 40 are supplied to the input side outside the reaction tank 60. Tank 42, gallium (Ga) supply tank 44, indium (In) supply tank 45, magnesium (Mg) supply tank 47, dimethylhydrazine (DMHy) supply tank 46, and hydrogen (or nitrogen or both) carrier gas supply An ammonia (NH ₃ ) gas cylinder 48 and a silicon (Si) supply gas cylinder 49 connected to the reaction tank 60 independently of the tank 40 are provided. An exhaust port is connected to the output side outside the reaction tank 60. In the configuration example of FIG. 16, ammonia, dimethylhydrazine and group III elements are separated in the raw material supply gas line to the reaction tank 60, but is not limited to such a configuration.

 The heating mechanism includes a heater, an infrared (IR) lamp, high frequency induction, and the like. The temperature of the susceptor heated by the heating mechanism is, for example, about 1050 ° C. or higher.

 For example, trimethylaluminum (TMAl), triethylaluminum (TEAl), or triisobutylaluminum (TIBAl) is applied to the aluminum (Al) supply tank 42.

 For example, trimethyl gallium (TMG), triethyl gallium (TEG), or tripropyl gallium (TPG) is applied to the gallium (Ga) supply tank 44.

 For example, trimethylindium (TMIn) or triethylindium (TEIn) is applied to the indium (In) supply tank 45.

For example, biscyclopentadienyl magnesium (Cp ₂ Mg) or bisethylcislopentadienyl magnesium (EtCp ₂ Mg) is applied to the magnesium (Mg) supply tank 47.

For example, silane (SiH ₄ ) or monomethylsilane (CH ₃ SiH ₃ ) is applied to the silicon raw material. The raw material is diluted to 1 to 100,000 ppm with hydrogen or nitrogen.

The crystal growth temperature of the Al _x Ga _1-x N layer is, for example, about 1050 ° C. or higher, 1050 ° C. to 1300 ° C., and preferably, for example, about 1260 ° C. to 1270 ° C. In some cases, it may be 1400 ° C. or higher.

The pressure of the reaction vessel 60 in the crystal growth of the Al _x Ga _1-x N layer is, for example, about 0.02 atm (atm) to about 0.3 atm, and preferably about 0.1 atm.

-MBE equipment-
FIG. 17 shows a schematic configuration of an MBE apparatus applied to the method for manufacturing the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention.

 As shown in FIG. 17, the MBE apparatus applied to the method for manufacturing the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention includes a substrate heater 74, a substrate holder 72, and a substrate 52 in a reaction vessel. Prepare.

The inner wall of the reaction tank is formed of a liquid nitrogen shroud 76, and the electron beam source 70, Ga cell 62, Al cell 64, In cell 67, Si cell 65, Mg cell 63, ammonia (NH) are formed outside the reaction tank. ₃ ) or an ammonia (NH ₃ ) cell or RF plasma source 66 and a RHEED screen 68 connected to a nitrogen (N ₂ ) gas cylinder 48.

 Further, the substrate 52 is irradiated with the electron beam 70 a from the electron beam source 70, and the diffracted electron beam 70 b is guided to the RHEED screen 68.

 Further, an exhaust port 54 is connected to an output side outside the reaction tank via an exhaust valve 78.

(Production method)
As shown in FIG. 4, the method for manufacturing an ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention includes a step of preparing an m-plane GaN substrate 10 and a method in which the c-axis is a main surface for crystal growth. Forming an AlGaN cladding layer 12 doped with an n-type impurity on the m-plane GaN substrate 10 with a plane inclined within a range of 40 ° to 90 ° from the line direction as a main surface for crystal growth; and an AlGaN cladding layer A step of forming an AlGaN waveguide layer 14 doped with an n-type impurity on the substrate 12, and a step of forming an Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 on the AlGaN waveguide layer 14. A step of forming an AlGaN waveguide layer 18 doped with a p-type impurity on the Al _X Ga _1-X N / Al _X Ga _1-X N active layer 16, and a p-type impurity on the AlGaN waveguide layer 18. Forming the AlGaN cladding layer 20 doped with sapphire A step of forming an AlGaN contact layer 22 doped with a p-type impurity on the AlGaN cladding layer 20, a step of forming a p-side electrode 26 in ohmic contact with the AlGaN contact layer 22, and the p-side electrode 26. A step of forming an n-side electrode 24 in ohmic contact with the m-plane GaN substrate 10 and a step of forming a reflecting surface of the resonator along the a-plane.

 A method for manufacturing the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention will be described in detail below.

-Manufacturing method using MOVPE-
(A) A substrate 52 wafer is held on a susceptor. In this state, a carrier gas and a nitrogen source gas (ammonia gas or dimethylhydrazine) are supplied to the reaction tube. Hydrogen, nitrogen, or both are used for the carrier gas. Further, the temperature of the wafer is raised by the heating mechanism 50. However, when a sapphire, SiC, LiAlO ₂ , or MgAl ₁₂ O ₄ substrate is used, the temperature is raised without supplying a nitrogen source gas in order to avoid nitriding of the surface of the substrate 52.

(B) After waiting until the substrate 52 wafer temperature reaches, for example, about 1050 ° C. or higher, aluminum source, gallium source, nitrogen source gas, and silicon source are supplied to the reaction tube, and silicon is added to the wafer surface. An n-type AlGaN cladding layer 12 and an n-type AlGaN waveguide layer 14 are grown.

(C) The AlGaN / AlGaN active layer 16 is grown. The supply flow ratio of the aluminum source and the gallium source is changed during the well layer growth and the barrier layer growth. This is repeated, for example, three times. During this growth, the supply of silicon raw material may be stopped.

(D) Next, a magnesium raw material is supplied to the reaction tube, and the p-type AlGaN waveguide layer 18, the p-type AlGaN cladding layer 20, and the p-type AlGaN contact layer 22 to which magnesium is added are grown.

(E) After the growth, a part of the AlGaN contact layer 22 and the AlGaN cladding layer 20 is processed into a stripe shape by using an etching technique such as RIE or focused ion beam (FIB), for example, along the c-axis. A ridge stripe structure is formed.

(F) A p-side electrode 26 in which, for example, Au / Ni metal or Pt / Au / Pd metal is laminated on the AlGaN contact layer 22 having a ridge stripe structure by a metal vapor deposition apparatus using resistance heating or electron beam. To form a separate confinement type structure. Similarly, the n-side electrode 24 in which, for example, Ti / Al metal is laminated on the back surface of the substrate 10 wafer is formed.

(G) A resonator is formed along the stripe direction. At this time, the end face is a-plane.

  The ultraviolet nitride semiconductor laser diode is manufactured through the above steps.

-Manufacturing method by MBE-
Aluminum raw material, gallium raw material, indium raw material, silicon raw material, and magnesium raw material are placed in a crucible of a Knudsen cell, evaporated by heater heating, and supplied as an atomic beam. The silicon raw material may be evaporated and supplied by electron beam or current heating. Moreover, you may use the organometallic raw material as described in the MOVPE method as an alternative of these raw materials.

(A) The substrate 52 wafer is held by the substrate holder 72. In order to improve the thermal conductivity in the ultra-high vacuum, a metal having good thermal conductivity may be deposited on the back surface of the substrate 52. In this state, nitrogen source gas (for example, ammonia gas or nitrogen plasma source) is supplied to the substrate 52. The wafer is heated by the heating mechanism (substrate heater 74). However, when a sapphire, SiC, LiAlO ₂ , or MgAl ₁₂ O ₄ substrate is used, the temperature is raised without supplying a nitrogen source gas in order to avoid nitriding of the substrate surface.

(B) After waiting until the wafer temperature reaches, for example, 800 to 1000 ° C. or higher, an aluminum source, a gallium source, a nitrogen source gas, and a silicon source are supplied to the substrate 52, and silicon is added to the wafer surface. An AlGaN cladding layer 12 and an n-type AlGaN waveguide layer 14 are grown. The surface morphology during growth is observed with an RHEED image.

(C) The AlGaN / AlGaN active layer 16 is grown. The supply flow ratio of the aluminum source and the gallium source is changed during the well layer growth and the barrier layer growth. This is repeated, for example, three times. During this growth, the supply of silicon raw material may be stopped.

(D) Next, a magnesium raw material is supplied to the substrate, and the p-type AlGaN waveguide layer 18, the p-type AlGaN cladding layer 20, and the p-type AlGaN contact layer 22 to which magnesium is added are grown.

(E) After the growth, a part of the AlGaN contact layer 22 and the AlGaN cladding layer 20 is processed into a stripe shape by using an etching technique such as RIE or focused ion beam (FIB), for example, along the c-axis. A ridge stripe structure is formed.

(F) A p-side electrode 26 in which, for example, Au / Ni metal or Pt / Au / Pd metal is laminated on the AlGaN contact layer 22 having a ridge stripe structure by a metal vapor deposition apparatus using resistance heating or electron beam. To form a separate confinement type structure. Similarly, the n-side electrode 24 in which, for example, Ti / Al metal is laminated on the back surface of the substrate 10 wafer is formed.

(G) A resonator is formed along the stripe direction. At this time, the end face is a-plane.

  An ultraviolet nitride semiconductor laser diode is produced by the above process.

In order to improve the efficiency of AlGaN-based LDs, dislocations / defects can be introduced by introducing lateral growth technology (LOG: Lateral Overgrowth) that does not propagate dislocations in the vertical direction or by introducing an AlN substrate that does not easily generate dislocations at the beginning of AlGaN growth. It is essential to reduce.

According to the ultraviolet nitride semiconductor light emitting device of the present invention, it is possible to realize an efficient optical waveguide that should be performed in parallel with dislocation / defect reduction, reduce an internal electric field effect due to polarization, and a nonpolar plane (a plane, The threshold current density can be reduced by the Al _x Ga _1-x N mixed crystal grown by m-plane) or semipolar plane growth or the LD structure using the quantum well as the active layer.

According to the ultraviolet nitride semiconductor light emitting device and the manufacturing method according to the first embodiment of the present invention, in order to emit ultraviolet light having a wavelength of 300 nm or less, the crystal growth plane is about 40 ° from the c-axis (polar plane). The internal field effect due to polarization is reduced by tilting to about 90 °, and an Al _x Ga _1-x N / Al _x Ga _1-x N multiple quantum well (MQW) structure is used for the light emitting layer, and the Al of the well layer By setting the mole fraction to 30% to 60% and further setting the mole fraction ratio of the Al mole fraction of the well layer to the Al mole fraction of the barrier layer to 0.7 or more, the in-plane of the well layer The compressive strain can be reduced, and the electric field vector E and the c-axis can be made parallel.

 Thereby, the threshold current density of the ultraviolet nitride semiconductor light emitting device (LD) can be reduced, and the light emission efficiency can be improved.

[Second Embodiment]
As shown in FIG. 8, the ultraviolet nitride semiconductor light emitting device according to the second embodiment of the present invention includes an m-plane substrate 10 and an AlGaN layer disposed on the m-plane substrate 10 and doped with an n-type impurity. 13 on the AlGaN layer 13 and on the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 and the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16. And an AlGaN layer 17 doped with p-type impurities, an AlGaN contact layer 22 doped on the AlGaN layer 17 and doped with p-type impurities, an AlGaN contact layer 22, and an AlGaN contact layer 22 The p-side electrode 26 is in ohmic contact with the p-side electrode 26 and is disposed on the m-plane substrate 10 so as to oppose the p-side electrode 26. The c-axis is the main surface of crystal growth. 40 degrees from the normal direction of 0 plane inclined in the range of ° to the principal plane of crystal growth, the electric field component of light E is characterized by indicating the polarization characteristics mainly made parallel to the c axis (E // c).

 In the ultraviolet nitride semiconductor light emitting device according to the second embodiment of the present invention, the main surface of crystal growth includes a nonpolar surface or a semipolar surface.

 In the ultraviolet nitride semiconductor light emitting device according to the second embodiment of the present invention, the nonpolar plane includes an m plane or an a plane.

 In the ultraviolet nitride semiconductor light emitting device according to the second embodiment of the present invention, the semipolar plane includes the {10-11} plane, the {10-12} plane, or the {11-22} plane, Any one is included.

 In the ultraviolet nitride semiconductor light emitting device according to the second embodiment of the present invention, any one of the m-plane, {10-11} plane, and {10-12} plane is used as the main plane of crystal growth. When the surface is selected, the a-plane is used as the reflector of the resonator.

 In the ultraviolet nitride semiconductor light emitting device according to the second embodiment of the present invention, the a-plane is a cleavage plane.

In the ultraviolet nitride semiconductor light emitting device according to the second embodiment of the present invention, the active layer has a single well or multiple quantum well structure, and the AlN molar fraction of the Al _x Ga _1-x N well layer is The ratio of the AlN molar fraction of the Al _x Ga _1-X N barrier layer to the AlN molar fraction of the Al _x Ga _1-X N well layer is 0.7 or higher.

 The m-plane substrate 10 has conductivity, and can be formed of, for example, a GaN substrate, an AlN substrate, or an AlGaN substrate.

The ultraviolet nitride semiconductor light emitting device according to the second embodiment of the present invention has a nonpolar plane as a crystal growth plane, and the stripe direction of the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 By making the cleavage plane a-plane, the horizontal transverse mode has gain and polarization guiding performance, while the vertical transverse mode is a relatively thick Al _x Ga _1-x N / Al _x Ga _1-x N active layer. 16 (for example, the number of wells of MQW is 3 or less and the total thickness is about 30 nm), and the optical confinement effect on the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 It becomes possible to use guided wave. As a result, compared with the first embodiment, the clad layer, the ridge stripe structure, and the waveguide layer are unnecessary, and the simplest configuration can be realized.

[Third embodiment]
As shown in FIG. 9, the ultraviolet nitride semiconductor light emitting device according to the third embodiment of the present invention includes an m-plane substrate 10 and an AlGaN contact disposed on the m-plane substrate 10 and doped with an n-type impurity. An AlGaN layer 13 disposed on the AlGaN contact layer 11 and doped with an n-type impurity; an Al _X Ga _1-X N / Al _X Ga _1-X N active layer disposed on the AlGaN layer 13; 16 and Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16, AlGaN layer 17 doped with p-type impurities, AlGaN layer 17 and p-type impurities The doped AlGaN contact layer 22, the p-side electrode 26 disposed on the AlGaN contact layer 22 and in ohmic contact with the AlGaN contact layer 22, and the same surface side as the p-side electrode 26 with respect to the m-plane substrate 10 surface The n-side electrode 24 is disposed on the AlGaN contact layer 11 exposed by etching from the surface of the AlGaN contact layer 22 and is in ohmic contact with the AlGaN contact layer 11, and the c-axis is the main surface of crystal growth. A plane inclined within a range of 40 ° to 90 ° from the normal direction is used as a main plane of crystal growth, and the electric field component E of light exhibits a polarization characteristic that is mainly parallel to the c-axis (E // c). And

 In the ultraviolet nitride semiconductor light emitting device according to the third embodiment of the present invention, the main surface of crystal growth includes a nonpolar plane or a semipolar plane.

 In the ultraviolet nitride semiconductor light emitting device according to the third embodiment of the present invention, the nonpolar plane includes an m plane or an a plane.

 In the ultraviolet nitride semiconductor light emitting device according to the third embodiment of the present invention, the semipolar plane includes the {10-11} plane, the {10-12} plane, or the {11-22} plane, Any one is included.

 In the ultraviolet nitride semiconductor light emitting device according to the third embodiment of the present invention, any one of the m-plane, {10-11} plane, and {10-12} plane is used as the main plane of crystal growth. When the surface is selected, the a-plane is used as the reflector of the resonator.

 In the ultraviolet nitride semiconductor light emitting device according to the third embodiment of the present invention, the a-plane is a cleavage plane.

In the ultraviolet nitride semiconductor light emitting device according to the third embodiment of the present invention, the active layer has a single well or multiple quantum well structure, and the AlN molar fraction of the Al _x Ga ₁ -xN well layer is The ratio of the AlN molar fraction of the Al _x Ga _1-X N barrier layer to the AlN molar fraction of the Al _x Ga _1-X N well layer is 0.7 or higher.

The m-plane substrate 10 may be composed of, for example, an insulating m-plane SiC substrate, an insulating m-plane AlN substrate, an insulating m-plane AlGaN substrate, an r-plane or m-plane sapphire substrate, and a (001) MgAl ₂ O ₄ substrate. it can.

The ultraviolet nitride semiconductor light emitting device according to the third embodiment of the present invention has a nonpolar plane as a crystal growth plane, and the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 has a stripe direction. By making the cleavage plane a-plane, the horizontal transverse mode has gain and polarization guiding performance, while the vertical transverse mode is a relatively thick Al _x Ga _1-x N / Al _x Ga _1-x N active layer. 16 (for example, the number of wells of MQW is 3 or less and the total thickness is about 30 nm), and the optical confinement effect on the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 It becomes possible to use guided wave.

 As a result, as compared with the first embodiment, a clad layer, a ridge stripe structure, and a waveguide layer are not required, and a simple configuration can be realized.

 In addition, the p-side electrode 26 and the n-side electrode 24 can be taken out from the same surface side, and mounting is facilitated.

[Fourth embodiment]
As shown in FIG. 10, the ultraviolet nitride semiconductor light emitting device according to the fourth embodiment of the present invention is arranged on an m-plane substrate 10 and an AlGaN conductive layer arranged on the m-plane substrate 10 and doped with an n-type impurity. Wave layer 14, AlGaN waveguide layer 14, Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16, Al _x Ga _1-x N / Al _x Ga _1-x N An AlGaN waveguide layer 18 disposed on the active layer 16 and doped with p-type impurities, an AlGaN contact layer 22 disposed on the AlGaN waveguide layer 18 and doped with p-type impurities, and an AlGaN contact layer 22 A p-side electrode 26 in ohmic contact with the AlGaN contact layer 22, an n-side electrode 24 disposed on the m-plane substrate 10 facing the p-side electrode 26 and in ohmic contact with the m-plane substrate 10, c-axis is the principal plane of crystal growth A plane inclined within a range of 40 ° to 90 ° from the linear direction is a main surface of crystal growth, and the electric field component E of light exhibits a polarization characteristic mainly parallel to the c-axis (E // c). To do.

 In the ultraviolet nitride semiconductor light emitting device according to the fourth embodiment of the present invention, the main surface of crystal growth includes a nonpolar plane or a semipolar plane.

 In the ultraviolet nitride semiconductor light emitting device according to the fourth embodiment of the present invention, the nonpolar plane includes an m plane or an a plane.

 In the ultraviolet nitride semiconductor light emitting device according to the fourth embodiment of the present invention, the semipolar plane includes a {10-11} plane, a {10-12} plane, or a {11-22} plane, Any one is included.

 In the ultraviolet nitride semiconductor light emitting device according to the fourth embodiment of the present invention, any one of the m-plane, {10-11} plane, and {10-12} plane is used as the main plane of crystal growth. When the surface is selected, the a-plane is used as the reflector of the resonator.

 In the ultraviolet nitride semiconductor light emitting device according to the fourth embodiment of the present invention, the a-plane is a cleavage plane.

In the ultraviolet nitride semiconductor light emitting device according to the fourth embodiment of the present invention, the active layer has a single well or multiple quantum well structure, and the AlN molar fraction of the Al _x Ga _1-x N well layer is The ratio of the AlN molar fraction of the Al _x Ga _1-X N barrier layer to the AlN molar fraction of the Al _x Ga _1-X N well layer is 0.7 or higher.

 The m-plane substrate 10 has conductivity, and can be formed of, for example, a GaN substrate, an AlN substrate, or an AlGaN substrate.

In the ultraviolet nitride semiconductor light emitting device according to the fourth embodiment of the present invention, the nonpolar plane is a crystal growth plane, and the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 has a stripe direction. By making the cleavage plane a-plane, the horizontal transverse mode has gain / polarized wave guiding performance, while the vertical transverse mode is sandwiched between the n-type AlGaN waveguide layer 14 and the p-type AlGaN waveguide layer 18 and is relatively thick _{Al X Ga 1-X N /} Al X Ga 1-X N active layer 16 (e.g., the number of wells of the MQW as 3 or less, about about 30nm in total thickness) by utilizing, Al _X Ga _{1 -X} N / Al _X Ga _{1 -X} N Waveguide can be used due to the optical confinement effect in the active layer 16.

 As a result, compared with the first embodiment, a clad layer and a ridge stripe structure are not required, and a relatively simple configuration can be realized.

[Fifth embodiment]
As shown in FIG. 11, the ultraviolet nitride semiconductor light emitting device according to the fifth embodiment of the present invention includes a substrate 10, an AlGaN contact layer 11 disposed on the substrate 10 and doped with an n-type impurity, An AlGaN waveguide layer 14 disposed on the AlGaN contact layer 11 and doped with an n-type impurity, and an Al _x Ga _1-x N / Al _x Ga _1-x N active layer disposed on the AlGaN waveguide layer 14 16, an Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16, an AlGaN waveguide layer 18 doped with a p-type impurity, and an AlGaN waveguide layer 18. AlGaN contact layer 22 doped with p-type impurities, p-side electrode 26 disposed on AlGaN contact layer 22 and in ohmic contact with AlGaN contact layer 22, and the same as p-side electrode 26 with respect to the surface of substrate 10 An n-side electrode 24 disposed on the surface side and disposed on the AlGaN contact layer 11 exposed by etching from the surface of the AlGaN contact layer 22 and in ohmic contact with the AlGaN contact layer 11; A surface inclined within a range of 40 ° to 90 ° from the normal direction of the surface is a main surface of crystal growth, and the electric field component E of light exhibits polarization characteristics mainly parallel to the c-axis (E // c). It is characterized by.

 In the ultraviolet nitride semiconductor light emitting device according to the fifth embodiment of the present invention, the main surface of crystal growth includes a nonpolar surface or a semipolar surface.

 In the ultraviolet nitride semiconductor light emitting device according to the fifth embodiment of the present invention, the nonpolar plane includes an m plane or an a plane.

 In the ultraviolet nitride semiconductor light emitting device according to the fifth embodiment of the present invention, the semipolar plane includes a {10-11} plane, a {10-12} plane, or a {11-22} plane, Any one is included.

 In the ultraviolet nitride semiconductor light-emitting device according to the fifth embodiment of the present invention, any one of the m-plane, the {10-11} plane, and the {10-12} plane is used as the main plane for crystal growth. When the surface is selected, the a-plane is used as the reflector of the resonator.

 In the ultraviolet nitride semiconductor light emitting device according to the fifth embodiment of the present invention, the a-plane is a cleavage plane.

In the ultraviolet nitride semiconductor light emitting device according to the fifth embodiment of the present invention, the active layer has a single well or multiple quantum well structure, and the AlN molar fraction of the Al _x Ga _1-x N well layer is The ratio of the AlN molar fraction of the Al _x Ga _1-X N barrier layer to the AlN molar fraction of the Al _x Ga _1-X N well layer is 0.7 or higher.

The substrate 10 can be composed of, for example, an insulating m-plane SiC substrate, an insulating m-plane AlN substrate, an insulating m-plane AlGaN substrate, an r-plane or m-plane sapphire substrate, and a (001) plane MgAl ₂ O ₄ substrate. .

The ultraviolet nitride semiconductor light emitting device according to the fifth embodiment of the present invention has a nonpolar plane as a crystal growth plane, and the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 has a stripe direction. By using the cleavage plane as the a-plane, the horizontal transverse mode has gain / polarization waveguide performance, while the vertical transverse mode is sandwiched between the n-type AlGaN waveguide layer 14 and the p-type AlGaN waveguide layer 18 and is relatively By using a thick Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 (for example, the number of MQW wells is 3 or less and the total thickness is about 30 nm), Al _x Ga _It is possible to use the guided wave due to the optical confinement effect in the _1-X N / Al _X Ga _1-X N active layer 16.

 As a result, compared with the first embodiment, a clad layer and a ridge stripe structure are not required, and a relatively simple configuration can be realized.

 In addition, the p-side electrode 26 and the n-side electrode 24 can be taken out from the same surface side, and mounting is facilitated.

[Sixth embodiment]
As shown in FIG. 12, the ultraviolet nitride semiconductor light emitting device according to the sixth embodiment of the present invention includes an m-plane substrate 10 and an AlGaN cladding disposed on the m-plane substrate 10 and doped with n-type impurities. Al _x Ga _{1 -x} N / Al _x Ga ₁ disposed on the layer 12, the AlGaN waveguide layer 14 disposed on the AlGaN cladding layer 12 and doped with n-type impurities, and the AlGaN waveguide layer 14. and _-X N active layer 16 is disposed on the _{Al X Ga 1-X N /} Al X Ga 1-X N active layer 16, an AlGaN waveguide layer 18 doped with p-type impurity, AlGaN waveguide layer 18 An AlGaN cladding layer 20 disposed on top and doped with p-type impurities, an AlGaN contact layer 22 disposed on the AlGaN cladding layer 20 and doped with p-type impurities, and an AlGa layer disposed on the AlGaN contact layer 22 A p-side electrode 26 that is in ohmic contact with the N contact layer 22; an n-side electrode 24 that is disposed on the m-plane substrate 10 so as to face the p-side electrode 26; Polarized light whose main surface for crystal growth is a plane inclined within a range of 40 ° to 90 ° from the normal direction of the main surface of crystal growth, and whose electric field component E is mainly parallel to the c-axis (E // c). It is characterized by exhibiting characteristics.

 In the ultraviolet nitride semiconductor light emitting device according to the sixth embodiment of the present invention, the main surface of crystal growth includes a nonpolar plane or a semipolar plane.

 In the ultraviolet nitride semiconductor light emitting device according to the sixth embodiment of the present invention, the nonpolar plane includes an m plane or an a plane.

 In the ultraviolet nitride semiconductor light emitting device according to the sixth embodiment of the present invention, the semipolar plane includes a {10-11} plane, a {10-12} plane, or a {11-22} plane, Any one is included.

 In the ultraviolet nitride semiconductor light-emitting device according to the sixth embodiment of the present invention, any one of the m-plane, the {10-11} plane, and the {10-12} plane is used as the main plane for crystal growth. When the surface is selected, the a-plane is used as the reflector of the resonator.

 In the ultraviolet nitride semiconductor light emitting device according to the sixth embodiment of the present invention, the a-plane is a cleavage plane.

In the ultraviolet nitride semiconductor light emitting device according to the sixth embodiment of the present invention, the active layer has a single well or multiple quantum well structure, and the AlN molar fraction of the Al _x Ga _1-x N well layer is The ratio of the AlN molar fraction of the Al _x Ga _1-X N barrier layer to the AlN molar fraction of the Al _x Ga _1-X N well layer is 0.7 or higher.

 The m-plane substrate 10 has conductivity, and can be formed of, for example, a GaN substrate, an AlN substrate, or an AlGaN substrate.

The ultraviolet nitride semiconductor light emitting device according to the sixth embodiment of the present invention has a nonpolar plane as a crystal growth plane, and the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 has a stripe direction. By using the cleavage plane as the a-plane, the horizontal transverse mode has gain and polarization guiding performance, while the vertical transverse mode is relatively thick Al _x Ga _1-x N / Al _x Ga _1-x N activity. By using the layer 16 (for example, the number of MQW wells is 3 or less and the total thickness is about 30 nm), the optical confinement in the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 is achieved. It is possible to use guided wave by effect.

 As a result, as compared with the first embodiment, a ridge stripe structure is unnecessary and a simple configuration can be realized.

[Seventh embodiment]
As shown in FIG. 13, the ultraviolet nitride semiconductor light emitting device according to the seventh embodiment of the present invention includes a substrate 10, an AlGaN contact layer 11 disposed on the substrate 10 and doped with an n-type impurity, An AlGaN cladding layer 12 disposed on the AlGaN contact layer 11 and doped with n-type impurities, an AlGaN waveguide layer 14 disposed on the AlGaN cladding layer 12 and doped with n-type impurities, and an AlGaN waveguide layer 14 Arranged on the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 and the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16, p-type An AlGaN waveguide layer 18 doped with impurities, an AlGaN cladding layer 20 doped with p-type impurities, and an AlGaN cladding layer 20 disposed on the AlGaN cladding layers 20, and doped with p-type impurities. The AlGaN contact layer 22 is disposed on the AlGaN contact layer 22, and the p-side electrode 26 is in ohmic contact with the AlGaN contact layer 22. The substrate 10 is disposed on the same surface side as the p-side electrode 26. The n-side electrode 24 is disposed on the AlGaN contact layer 11 exposed from the surface of the AlGaN contact layer 22 by etching, and is in ohmic contact with the AlGaN contact layer 11. The c-axis is a normal line of the main surface of crystal growth A plane inclined within a range of 40 ° to 90 ° from the direction is a main plane of crystal growth, and the electric field component E of light mainly exhibits polarization characteristics parallel to the c-axis (E // c). .

 In the ultraviolet nitride semiconductor light emitting device according to the seventh embodiment of the present invention, the main surface of crystal growth includes a nonpolar plane or a semipolar plane.

 In the ultraviolet nitride semiconductor light emitting device according to the seventh embodiment of the present invention, the nonpolar plane includes an m plane or an a plane.

 In the ultraviolet nitride semiconductor light emitting device according to the seventh embodiment of the present invention, the semipolar plane includes a {10-11} plane, a {10-12} plane, or a {11-22} plane, Any one is included.

 In the ultraviolet nitride semiconductor light-emitting device according to the seventh embodiment of the present invention, any one of the m-plane, the {10-11} plane, and the {10-12} plane is used as the main plane for crystal growth. When the surface is selected, the a-plane is used as the reflector of the resonator.

 In the ultraviolet nitride semiconductor light emitting device according to the seventh embodiment of the present invention, the a-plane is a cleavage plane.

In the ultraviolet nitride semiconductor light emitting device according to the seventh embodiment of the present invention, the active layer has a single well or multiple quantum well structure, and the AlN molar fraction of the Al _x Ga _1-x N well layer is The ratio of the AlN molar fraction of the Al _x Ga _1-X N barrier layer to the AlN molar fraction of the Al _x Ga _1-X N well layer is 0.7 or higher.

The substrate 10 can be composed of, for example, an insulating m-plane SiC substrate, an insulating m-plane AlN substrate, an insulating m-plane AlGaN substrate, an r-plane or m-plane sapphire substrate, and a (001) plane MgAl ₂ O ₄ substrate. .

In the ultraviolet nitride semiconductor light emitting device according to the seventh embodiment of the present invention, the nonpolar plane is the crystal growth plane, and the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 has a stripe direction. By using the cleavage plane as the a-plane, the horizontal transverse mode has gain and polarization guiding performance, while the vertical transverse mode is relatively thick Al _x Ga _1-x N / Al _x Ga _1-x N activity. By using the layer 16 (for example, the number of MQW wells is 3 or less and the total thickness is about 30 nm), the optical confinement in the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 is achieved. It is possible to use guided wave by effect.

 As a result, as compared with the first embodiment, a ridge stripe structure is unnecessary and a relatively simple configuration can be realized.

 In addition, the p-side electrode 26 and the n-side electrode 24 can be taken out from the same surface side, and mounting is facilitated.

[Eighth embodiment]
As shown in FIG. 14, the ultraviolet nitride semiconductor light emitting device according to the eighth embodiment of the present invention is disposed on the m-plane GaN substrate 10 and the m-plane GaN substrate 10 and is doped with n-type impurities. AlGaN cladding layer 12, AlGaN waveguide layer 14 disposed on AlGaN cladding layer 12 and doped with n-type impurities, AlGaN waveguide layer 14, Al _X Ga _1-X N / Al _X Ga _{A 1-X} N active layer 16; an AlGaN waveguide layer 18 disposed on the Al _X Ga _1-X N / Al _X Ga _1-X N active layer 16 and doped with a p-type impurity; and an AlGaN waveguide layer 18, an AlGaN cladding layer 20 doped with p-type impurities, an AlGaN contact layer 22 disposed on the AlGaN cladding layer 20 and having a ridge stripe structure and doped with p-type impurities, and AlGa A p-side electrode 26 disposed on the N-contact layer 22 and in ohmic contact with the AlGaN contact layer 22, and disposed on the m-plane GaN substrate 10 so as to face the p-side electrode 26 and in ohmic contact with the m-plane GaN substrate 10 And a side electrode 24, and a surface in which the c-axis is inclined within a range of 40 ° to 90 ° from the normal direction of the main surface of crystal growth is a main surface of crystal growth, and an electric field component E of light is mainly c-axis. And a polarization characteristic parallel to (E // c).

 In the ultraviolet nitride semiconductor light emitting device according to the eighth embodiment of the present invention, the main surface of crystal growth includes a nonpolar plane or a semipolar plane.

 In the ultraviolet nitride semiconductor light emitting device according to the eighth embodiment of the present invention, the nonpolar plane includes an m plane or an a plane.

 In the ultraviolet nitride semiconductor light emitting device according to the eighth embodiment of the present invention, the semipolar plane includes the {10-11} plane, the {10-12} plane, or the {11-22} plane, Any one is included.

 In the ultraviolet nitride semiconductor light emitting device according to the eighth embodiment of the present invention, any one of the m-plane, the {10-11} plane, and the {10-12} plane is used as the main surface for crystal growth. When the surface is selected, the a-plane is used as the reflector of the resonator.

 In the ultraviolet nitride semiconductor light-emitting device according to the eighth embodiment of the present invention, the a-plane is a cleaved surface.

In the ultraviolet nitride semiconductor light emitting device according to the eighth embodiment of the present invention, the active layer has a single well or multiple quantum well structure, and the AlN molar fraction of the Al _x Ga ₁ -xN well layer is The ratio of the AlN molar fraction of the Al _x Ga _1-X N barrier layer to the AlN molar fraction of the Al _x Ga _1-X N well layer is 0.7 or higher.

 The m-plane substrate 10 has conductivity, and can be formed of, for example, a GaN substrate, an AlN substrate, or an AlGaN substrate.

The ultraviolet nitride semiconductor light emitting device according to the eighth embodiment of the present invention uses the nonpolar plane as the crystal growth plane and the cleavage plane in the stripe direction as the a plane, so that the horizontal transverse mode is gain / polarization guided. The vertical transverse mode has an Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 (for example, the number of MQW wells is 3 or less and the total thickness is about 30 nm). By using this, it becomes possible to use the guided wave due to the light confinement effect on the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16.

[Ninth embodiment]
As shown in FIG. 15, the ultraviolet nitride semiconductor light emitting device according to the ninth embodiment of the present invention includes a substrate 10, an AlGaN contact layer 11 disposed on the substrate 10 and doped with an n-type impurity, An AlGaN cladding layer 12 disposed on the AlGaN contact layer 11 and doped with n-type impurities, an AlGaN waveguide layer 14 disposed on the AlGaN cladding layer 12 and doped with n-type impurities, and an AlGaN waveguide layer 14 Arranged on the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 and the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16, p-type An AlGaN waveguide layer 18 doped with impurities, an AlGaN cladding layer 20 doped with p-type impurities, and an AlGaN cladding layer 20 disposed on the AlGaN waveguide layer 18, and a ridge stripe An AlGaN contact layer 22 doped with a p-type impurity, a p-side electrode 26 disposed on the AlGaN contact layer 22 and in ohmic contact with the AlGaN contact layer 22, and a p-side relative to the surface of the substrate 10 An n-side electrode 24 disposed on the same surface side as the electrode 26 and disposed on the AlGaN contact layer 11 exposed by etching from the surface of the AlGaN contact layer 22 and having an ohmic contact with the AlGaN contact layer 11 is provided. Polarized light whose main surface for crystal growth is a plane inclined within a range of 40 ° to 90 ° from the normal direction of the main surface of crystal growth, and whose electric field component E is mainly parallel to the c-axis (E // c). It is characterized by exhibiting characteristics.

 In the ultraviolet nitride semiconductor light emitting device according to the ninth embodiment of the present invention, the main surface of crystal growth includes a nonpolar surface or a semipolar surface.

 In the ultraviolet nitride semiconductor light emitting device according to the ninth embodiment of the present invention, the nonpolar plane includes an m plane or an a plane.

 In the ultraviolet nitride semiconductor light emitting device according to the ninth embodiment of the present invention, the semipolar plane includes a {10-11} plane, a {10-12} plane, or a {11-22} plane, Any one is included.

 In the ultraviolet nitride semiconductor light emitting device according to the ninth embodiment of the present invention, any one of the m-plane, {10-11} plane, and {10-12} plane as the main plane of crystal growth is used. When the surface is selected, the a-plane is used as the reflector of the resonator.

 The ultraviolet nitride semiconductor light-emitting device according to the ninth embodiment of the present invention is characterized in that the a-plane is a cleavage plane.

In the ultraviolet nitride semiconductor light emitting device according to the ninth embodiment of the present invention, the active layer has a single well or multiple quantum well structure, and the AlN molar fraction of the Al _x Ga _1-x N well layer is The ratio of the AlN molar fraction of the Al _x Ga _1-X N barrier layer to the AlN molar fraction of the Al _x Ga _1-X N well layer is 0.7 or higher.

The substrate 10 can be composed of, for example, an insulating m-plane SiC substrate, an insulating m-plane AlN substrate, an insulating m-plane AlGaN substrate, an r-plane or m-plane sapphire substrate, and a (001) plane MgAl ₂ O ₄ substrate. .

The ultraviolet nitride semiconductor light emitting device according to the ninth embodiment of the present invention uses the nonpolar plane as the crystal growth plane and the cleavage plane in the stripe direction as the a plane, so that the horizontal transverse mode is gain / polarization guided. The vertical transverse mode has an Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16 (for example, the number of MQW wells is 3 or less and the total thickness is about 30 nm). By using this, it becomes possible to use the guided wave due to the light confinement effect on the Al _x Ga _1-x N / Al _x Ga _1-x N active layer 16.

 In addition, the p-side electrode 26 and the n-side electrode 24 can be taken out from the same surface side, and mounting is facilitated.

[Tenth embodiment]
FIG. 22A shows the oscillation wavelength of the laser light in the ultraviolet nitride semiconductor light emitting device including the Al _1-X In _X N / Al _1-X In _X N active layer according to the tenth embodiment of the present invention. The relationship with InN molar fraction x is shown. FIG. 22B shows the relationship between the band gap energy and the InN molar fraction x in the ultraviolet nitride semiconductor light emitting device according to the tenth embodiment of the present invention.

FIG. 23 shows band gap energy and a-axis lattice constant in an ultraviolet nitride semiconductor light emitting device having an Al _{1 -X} In _X N / Al _{1 -X} In _X N active layer according to a tenth embodiment of the present invention. And the relationship between the emission wavelength and the lattice constant of the a axis.

 The ultraviolet nitride semiconductor light emitting device according to the tenth embodiment of the present invention is characterized in that AlInN is applied instead of AlGaN in the configuration of the ultraviolet nitride semiconductor light emitting device according to the first embodiment. Have.

The ultraviolet nitride semiconductor light emitting device according to the tenth embodiment of the present invention is arranged on an m-plane substrate, an AlInN layer that is arranged on the m-plane substrate and doped with an n-type impurity, and an AlInN layer. An Al _{1 -X} In _X N / Al _{1 -X} In _X N active layer having a quantum well structure comprising an Al _{1 -X} In _X N barrier layer and an Al _{1 -X} In _X N well layer, and an Al _{1 -X} In disposed _{X N / Al 1-X in} X N active layer, and a AlInN doped with p-type impurity layer, the range c-axis from the normal direction of the principal surface of the crystal growth of 40 ° to 90 ° The tilted surface is the main surface of crystal growth, and the electric field component E of light mainly exhibits polarization characteristics parallel to the c-axis (E // c).

 In the ultraviolet nitride semiconductor light emitting device according to the tenth embodiment of the present invention, the main surface of crystal growth includes a nonpolar plane or a semipolar plane.

 In the ultraviolet nitride semiconductor light emitting device according to the tenth embodiment of the present invention, the nonpolar plane includes an m plane or an a plane.

 In the ultraviolet nitride semiconductor light emitting device according to the tenth embodiment of the present invention, the semipolar plane includes a {10-11} plane, a {10-12} plane, or a {11-22} plane, Any one is included.

 In the ultraviolet nitride semiconductor light emitting device according to the tenth embodiment of the present invention, any one of the m-plane, {10-11} plane, and {10-12} plane as the main plane of crystal growth is used. When the surface is selected, the a-plane is used as the reflector of the resonator.

 In the ultraviolet nitride semiconductor light emitting device according to the tenth embodiment of the present invention, the a-plane is a cleavage plane.

 In the ultraviolet nitride semiconductor light emitting device according to the tenth embodiment of the present invention, the active layer has a single well or multiple quantum well structure and has an InN molar fraction of 5% or less. .

The substrate 10 can be composed of, for example, an insulating m-plane SiC substrate, an insulating m-plane AlN substrate, an insulating m-plane AlGaN substrate, an r-plane or m-plane sapphire substrate, and a (001) plane MgAl ₂ O ₄ substrate. .

The ultraviolet nitride semiconductor light emitting device according to the tenth embodiment of the present invention uses a nonpolar plane as a crystal growth plane and a cleavage plane in the stripe direction as an a plane, so that the horizontal transverse mode is a gain / polarization waveguide. The vertical transverse mode uses an Al _{1 -X} In _X N / Al _{1 -X} In _X N active layer (for example, the number of MQW wells is 3 or less and the total thickness is about 30 nm). This makes it possible to use guided wave due to the optical confinement effect in the Al _{1 -X} In _X N / Al _{1 -X} In _X N active layer.

 In the ultraviolet nitride semiconductor light emitting device according to the tenth embodiment of the present invention, in the configuration of the ultraviolet nitride semiconductor light emitting device according to the second to ninth embodiments as well as the first embodiment, It is also possible to adopt a configuration in which AlInN is applied instead of AlGaN.

According to the ultraviolet nitride semiconductor light emitting device of the present invention, an efficient optical waveguide can be realized, the internal electric field effect due to polarization can be reduced, and nonpolar plane (a plane, m plane) or semipolar plane grown Al Low threshold current density can be achieved by a _1-X In _X N mixed crystal or an LD structure using the quantum well as an active layer.

According to the ultraviolet nitride semiconductor light emitting device of the tenth embodiment of the present invention, in order to emit ultraviolet light having a wavelength of 300 nm or less, the crystal growth plane is about 40 ° to 90 ° from the c-axis (polar plane). By reducing the internal electric field effect due to polarization by tilting to a certain extent, and using an Al _1-X In _X N / Al _1-X In _X N MQW structure in the light emitting layer, the InN molar fraction is made 5% or less. The in-plane compressive strain of the well layer can be reduced, and the electric field vector E and the c-axis can be made parallel.

 Thereby, the threshold current density of the ultraviolet nitride semiconductor light emitting device (LD) can be reduced, and the light emission efficiency can be improved.

[Other embodiments]
The first to tenth embodiments of the present invention have been described above. However, the description and the drawings that constitute a part of this disclosure do not limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

 In the embodiments of the present invention, the semiconductor laser diode has been mainly described, but it is obvious that the present invention can also be applied to a light emitting diode.

 As described above, the present invention has been described according to the first to tenth embodiments, but it is needless to say that the present invention includes various embodiments that are not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

 According to the ultraviolet nitride semiconductor light emitting device and the manufacturing method thereof according to the embodiment of the present invention, a low threshold current density of a nitride semiconductor laser diode that generates laser light having a deep ultraviolet wavelength made of a group III nitride semiconductor Therefore, we provide essential light sources in a wide range of fields such as sterilization / water purification, medical equipment, biochemical industry, and semiconductor lithography.

2 is a comparison of band diagrams of a GaN layer and an AlN layer applied to the ultraviolet nitride semiconductor light emitting device according to the first embodiment of the present invention, wherein (a) a band diagram at the Γ point of GaN, (b) AlN Band diagram at Γ point. (A) Dependence of band ordering on top of valence band of unstrained Al _X Ga _1-X N mixed crystal depending on AlN mole fraction x, (b) Al _X subjected to in-plane tensile strain on unstrained GaN substrate Dependence of strain ε _zz (%) in the c-axis direction of Ga _1-X N mixed crystal on AlN mole fraction x. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram for demonstrating the nonpolar surface applied to the ultraviolet nitride semiconductor light-emitting device based on the 1st Embodiment of this invention, and a semipolar surface, Comprising: (a) The crystal structure of a group III nitride semiconductor is shown. (B) Schematic diagram for explaining the m-plane {1-100} and a-plane {11-20} which are nonpolar planes, (c) for explaining the semipolar plane {10-11} (D) The schematic diagram for demonstrating semipolar surface {10-12}, (e) The schematic diagram for demonstrating semipolar surface {11-22}. 1 is a schematic bird's-eye view of an ultraviolet nitride semiconductor light emitting device according to a first embodiment of the present invention, and is a conceptual diagram of an LD in which an AlGaN / AlGaN active layer 16 having an MQW structure is formed on an m-plane GaN substrate 10. 1 is a schematic bird's-eye view of an ultraviolet nitride semiconductor light emitting device according to a comparative example of the present invention, and is a conceptual diagram of an LD in which an AlW / AlGaN active layer 160 having an MQW structure is formed on a c-plane GaN substrate 100. FIG. (A) A diagram showing a waveguide mode (Ec: TE mode) when the c-plane is used as the resonator mirror surfaces 28a and 28b. (B) When the a-plane is used as the resonator mirror surfaces 30a and 30b. The figure showing waveguide mode (E // c: TE mode). The strain of ε _zz (%) in the c-axis direction generated in the Al _Y Ga _1-Y N well layer laminated on the unstrained Al _X Ga _1-X N barrier layer is that of the Al _X Ga _1-X N barrier layer. AlN mole fraction x dependence. The typical cross-section figure of the ultraviolet nitride semiconductor light-emitting device concerning the 2nd Embodiment of this invention. The typical cross-section figure of the ultraviolet nitride semiconductor light-emitting device which concerns on the 3rd Embodiment of this invention. The typical cross-section figure of the ultraviolet nitride semiconductor light emitting element concerning the 4th Embodiment of this invention. The typical cross-section figure of the ultraviolet nitride semiconductor light-emitting device concerning the 5th Embodiment of this invention. The typical cross-section figure of the ultraviolet nitride semiconductor light-emitting device concerning the 6th Embodiment of this invention. The typical cross-section figure of the ultraviolet nitride semiconductor light-emitting device which concerns on the 7th Embodiment of this invention. The typical cross-section figure of the ultraviolet nitride semiconductor light-emitting device concerning the 8th Embodiment of this invention. The typical cross-section figure of the ultraviolet nitride semiconductor light-emitting device which concerns on the 9th Embodiment of this invention. The typical block diagram of the MOVPE apparatus applied to the manufacturing method of the ultraviolet nitride semiconductor light-emitting device based on the 1st Embodiment of this invention. The typical block diagram of the MBE apparatus applied to the manufacturing method of the ultraviolet nitride semiconductor light-emitting device concerning the 1st Embodiment of this invention. (A) is a figure which shows the relationship between the oscillation wavelength of a laser beam and the AlN molar fraction x in the ultraviolet nitride semiconductor light-emitting device based on the 1st Embodiment of this invention, (b) 1st of this invention The figure which shows the relationship between the band gap energy and the AlN molar fraction x in the ultraviolet nitride semiconductor light-emitting device which concerns on embodiment. The figure which shows the relationship between the hole density and distance which takes one structure of GaN / InGaN blue-violet LD as an example, Comprising: The figure explaining the non-uniform hole distribution to a MQW active layer. The figure which shows the relationship of the hole density and distance which takes another structure of GaN / InGaN blue-violet LD as an example, Comprising: The figure explaining the non-uniform hole distribution to a MQW active layer. The figure which shows the relationship between the threshold current density J (kA / cm < ² >) and the number of InGaN wells in GaN / InGaN blue-violet LD. (A) Laser light oscillation wavelength and InN mole fraction in an ultraviolet nitride semiconductor light emitting device including an Al _{1 -X} In _X N / Al _{1 -X} In _X N active layer according to a tenth embodiment of the present invention The figure which shows the relationship between x, (b) The figure which shows the relationship between the band gap energy and InN molar fraction x in the ultraviolet nitride semiconductor light-emitting device concerning the 10th Embodiment of this invention. The relationship between the band gap energy and the a-axis lattice constant in the ultraviolet nitride semiconductor light emitting device including the Al _{1 -X} In _X N / Al _{1 -X} In _X N active layer according to the tenth embodiment of the present invention, and The figure which shows the relationship between the light emission wavelength and the lattice constant of an a axis.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Board | substrate 11 ... AlGaN contact layer 12, 20 ... AlGaN clad layer 13, 17 ... AlGaN layer 14, 18 ... AlGaN waveguide layer 16 ... AlGaN / AlGaN active layer 22 ... AlGaN contact layer 24 ... n side electrode 26 ... p side Electrodes 28a, 28b, 30a, 30b ... resonant mirror surface 40 ... hydrogen carrier gas tank 42 ... aluminum (Al) supply tank 44 ... gallium (Ga) supply tank 45 ... indium (In) supply tank 46 ... dimethylhydrazine (DMHy) supply Tank 47 ... Magnesium (Mg) supply tank 48 ... Ammonia (NH ₃ ) or nitrogen (N ₂ ) gas cylinder 49 ... Gas cylinder 50 for supplying silicon (Si) ... Heating mechanism 52 ... Substrate 54 ... Exhaust port 56 ... Susceptor 60 ... Reaction tank 62 ... Ga cell 63 ... Mg cells 64 ... Al cell 65 ... Si cell 66 ... NH ₃ cells Other RF plasma source 67 ... an In cell 68 ... RHEED screen 70 ... electron beam source 70a, 70b ... electron beam 72 ... substrate holder 74 ... substrate heater 76 ... liquid nitrogen shroud 78 ... exhaust valve

Claims (16)

Any one of a nonpolar plane substrate and a semipolar plane substrate ;
An AlGaN layer disposed on the substrate and doped with an n-type impurity;
Wherein disposed on the AlGaN _{layer, Al X Ga 1-X N} (0 ≦ x ≦ 1) barrier layer and the _{Al X Ga 1-X N (} 0 ≦ x ≦ 1) Al X having a quantum well structure composed of the well layer A Ga _1-X N / Al _X Ga _1-X N active layer;
The _{Al X Ga 1-X N /} Al X Ga 1-X N is disposed on the active layer, and a AlGaN layer doped with p-type impurity,
The plane in which the c-axis is inclined within the range of 40 ° to 90 ° from the normal direction of the main plane of crystal growth is the main plane of crystal growth, and the electric field component E of light is mainly parallel to the c-axis (E // c ) polarization characteristics shows comprising, an end face of the crystal growth surface in the laser resonator formed on the crystal grown above the active layer is formed in a plane, the c-axis is in the quantum well plane of the active layer An ultraviolet nitride semiconductor light emitting device characterized in that the number of wells in the active layer is 3 or less . On the main surface of the crystal growth, if you choose the non-polar plane substrate, a non-polar surface is included, if you choose the semipolar plane substrate, semipolar plane is included, the selection of the semipolar surface 2. The ultraviolet nitride semiconductor light emitting device according to claim 1 , wherein an angle formed with the c-axis is continuously and arbitrarily changed within a range of 40 ° to 90 ° . The nonpolar plane includes an m plane when an m plane substrate is selected as the nonpolar plane substrate, and an a plane when an a plane substrate is selected as the nonpolar plane substrate. The ultraviolet nitride semiconductor light-emitting device according to claim 2. When the semipolar plane substrate is selected, the semipolar plane includes any one of {10-11} plane, {10-12} plane, and {11-22} plane. The ultraviolet nitride semiconductor light-emitting device according to claim 2.   When any one of the m-plane, {10-11} plane, or {10-12} plane is selected as the principal plane for crystal growth, the a-plane is used as a reflector of the resonator. The ultraviolet nitride semiconductor light-emitting device according to claim 1.   The ultraviolet nitride semiconductor light emitting device according to claim 5, wherein the a-plane is a cleavage plane. The active layer has a single well or multiple quantum well structure, and the Al _X Ga _1-X N well layer has an AlN molar fraction of 30% to 60%, and the Al _X Ga _1-X 2. The ultraviolet nitride semiconductor light emitting device according to claim 1, wherein the ratio of the AlN mole fraction of the N barrier layer to the AlN mole fraction of the Al _X Ga _1-X N well layer is 0.7 or more. . an m-plane substrate;
An AlInN layer disposed on the m-plane substrate and doped with an n-type impurity;
Al _{1 -X} In _X N / Al _{1 -X} In _X N activity having a quantum well structure comprising an Al _{1 -X} In _X N barrier layer and an Al _{1 -X} In _X N well layer disposed on the AlInN layer Layers,
The _{Al 1-X In X N /} Al 1-X In X N are arranged on the active layer, and a AlInN layer doped with p-type impurity,
The plane in which the c-axis is inclined within the range of 40 ° to 90 ° from the normal direction of the main plane of crystal growth is the main plane of crystal growth, and the electric field component E of light is mainly parallel to the c-axis (E // c ) polarization characteristics shows comprising, an end face of the crystal growth surface in the laser resonator formed on the crystal grown above the active layer is formed in a plane, the c-axis is in the quantum well plane of the active layer An ultraviolet nitride semiconductor light emitting device characterized in that the number of wells in the active layer is 3 or less .   9. The ultraviolet nitride semiconductor light emitting device according to claim 8, wherein the active layer has a single well or multiple quantum well structure and has an InN molar fraction of 5% or less. preparing an m-plane substrate;
Forming an AlGaN layer doped with an n-type impurity on the m-plane substrate, with the c-axis inclined in the range of 40 ° to 90 ° from the normal direction of the main surface of crystal growth as the main surface of crystal growth And a process of
The AlGaN Al on the layer _X Ga _1-X N barrier layers and Al _X Ga _1-X N of the well number of the quantum well structure consisting of well layers possess the active layer 3 to less Al _X Ga ₁ forming a _{-X N / Al X Ga 1-} X N active layer,
Forming an AlGaN layer doped with a p-type impurity on the Al _x Ga _1-x N / Al _x Ga _1-x N active layer;
and a step of forming a reflection surface of the laser resonator along the a-plane.   11. The method of manufacturing an ultraviolet nitride semiconductor light emitting device according to claim 10, wherein the step of forming the reflection surface of the laser resonator along the a-plane has a cleavage.   The method of manufacturing an ultraviolet nitride semiconductor light emitting device according to claim 10, wherein the n-type impurity is Si and the p-type impurity is Mg.   9. The ultraviolet nitride semiconductor light-emitting device according to claim 1, wherein the c-axis exists in a quantum well plane of the active layer.   The method of manufacturing an ultraviolet nitride semiconductor light emitting device according to claim 10, wherein the c-axis exists in a quantum well plane of the active layer.   9. The ultraviolet nitride semiconductor light emitting device according to claim 1, wherein the number of wells in the active layer is 2 or less.   The method of manufacturing an ultraviolet nitride semiconductor light emitting device according to claim 10, wherein the number of wells in the active layer is 2 or less.