JP4424840B2 - III-N compound semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device manufactured on a III-N compound semiconductor substrate, particularly a GaN compound semiconductor substrate, and more particularly to a light emitting element.
[0002]
[Prior art]
Conventionally, GaN-based compound semiconductors have been used or studied as light-emitting elements or high-power devices using their characteristics. For example, when a light-emitting element is manufactured, it can be technically used as a light-emitting element having a wide range from purple to orange by adjusting the composition of the light-emitting element.
[0003]
In recent years, blue light emitting diodes and green light emitting diodes have been put to practical use by utilizing the characteristics, and blue-violet semiconductor lasers have been developed as semiconductor laser elements.
[0004]
When manufacturing a GaN-based compound semiconductor film, a substrate made of sapphire, SiC, spinel, Si, GaAs, or the like is used as the substrate. For example, when sapphire is used as a substrate, a GaN or ALN buffer layer is formed in advance at a low temperature of about 550 ° C. before epitaxial growth of the GaN film, and then the substrate is heated to a high temperature of about 1050 ° C. It is known that when a GaN-based compound semiconductor film is epitaxially grown, a crystal having a good surface state and a good structural and electrical property can be obtained.
[0005]
In addition, when using SiC as a substrate, it is known that a thin AlN film should be used as a buffer layer at a growth temperature for epitaxial growth. However, if a substrate other than a GaN compound semiconductor is used, a large number of defects are produced in the manufactured GaN compound semiconductor due to differences in thermal expansion coefficient and lattice constant between the GaN compound semiconductor film to be grown and the substrate. Will occur. The defects are classified into edge dislocations and screw dislocations, and the total density is about 1 × 10. ⁹ cm ^-2 ~ 1x10 ^Ten cm ^-2 It also becomes a degree. These defects are known to trap carriers and impair the electrical properties of the prepared film. In addition, it is known to reduce the lifetime of lasers that carry large currents. Yes.
[0006]
For this reason, studies have been made to reduce these defects and to improve the electrical characteristics of the semiconductor to be prepared. For example, in order to suppress the increase of defects such as dislocations on a GaN film grown by metal organic chemical vapor deposition (MOCVD) method or the like, ₂ A technology has been developed for growing a GaN thick film by a hydride vapor phase epitaxy (H-VPE) method using a mask of tungsten or the like, and using the obtained thick film as a substrate to produce a light emitting device thereon. ing.
[0007]
[Problems to be solved by the invention]
However, the characteristics of the n-type electrode on such a GaN substrate were not clear. The present inventors have clarified that when an n-type electrode such as Ti / Al is formed on the Ga termination surface of a GaN substrate, the electrode has a strong tendency to exhibit Schottky characteristics. The present inventors considered that carbon (C) or the like is easily bonded to Ga dangling bonds on the Ga termination surface. When an n-type electrode such as Ti / Al is formed on the Ga termination surface in the presence of C, a barrier layer is formed and the electrode can exhibit Schottky characteristics. On the other hand, a film of Ni, Pd or the like that is a p-type electrode can take in carbon (C) or the like and reduce the barrier layer. This was considered to be one of the reasons why the ohmic characteristics are relatively easily obtained for the p-type electrode.
[0008]
In order to obtain an n-type electrode such as ohmic Ti / Al on the Ga termination surface of the GaN substrate, the substrate surface is cleaned with hydrochloric acid or the like, or heat treatment for alloy formation is performed after the electrode is formed. And an intermediate product of Ti in contact therewith, it was necessary to include a step of reducing the barrier layer. However, even if such a process was introduced, the contact specific resistance with the n-type electrode was high.
[0009]
One object of the present invention is to provide a technique for obtaining ohmic characteristics by forming an n-type electrode on a semiconductor device structure using a nitride semiconductor substrate, for example, a GaN substrate, without performing the above-described surface treatment or heat treatment step. There is.
[0010]
Another object of the present invention is to provide a nitride semiconductor device, particularly a light emitting element, having a low contact specific resistance of an n-type electrode.
[0011]
A further object of the present invention is to provide a nitride semiconductor device, particularly a light emitting element, having a low threshold voltage or a low threshold current density.
[0012]
The present inventors have found that ohmic characteristics can be easily obtained if an n-type electrode is formed on the N termination surface of a nitride semiconductor. Furthermore, the inventor has clarified the relationship between the impurity concentration added to the nitride semiconductor substrate and the contact specific resistance of the n-electrode. Further, the present inventors have made a relation between the impurity concentration added to the nitride semiconductor substrate and the threshold voltage and the relationship between the impurity concentration added to the nitride semiconductor substrate and the threshold current density for the light-emitting element, particularly the laser diode element. And an appropriate impurity concentration that provides a low contact specific resistance, a low threshold voltage, or a low threshold current density. The present invention is based on the above findings.
[0013]
[Means for Solving the Problems]
According to the present invention, a III-N compound semiconductor device is provided, and the device has an electrode on the nitrogen termination surface of the III-N compound semiconductor substrate. Specifically, a semiconductor device according to the present invention includes a III-N compound semiconductor substrate, a plurality of III-N compound semiconductor layers formed on the semiconductor substrate, and a plurality of semiconductor layers formed on the semiconductor substrate. N-type electrode and p-type electrode for applying a voltage to the semiconductor substrate, wherein the semiconductor substrate is n-type, and the n-type electrode is formed on a nitrogen termination surface of the semiconductor substrate.
[0014]
FIG. 23 shows a Ga termination surface and an N termination surface of GaN grown on the (0001) plane of the seed substrate. In the figure, 2301 is a seed substrate, 2302 is a buffer layer, 2303a is a Ga termination surface, 2303b is an N termination surface, white circle 2304 is Ga atom, and black circle 2305 is N atom. As shown in the figure, N atoms 2305 preferentially protrude from the N termination surface 2303b, while Ga atoms 2304 preferentially protrude from the Ga termination surface 2303a.
[0015]
Here, the N termination plane and the Ga termination plane with respect to the (0001) plane of the GaN crystal can be defined as follows. When the crystal having an exposed N terminal surface is immersed in a 1.8 M NaOH solution at room temperature for 3 minutes, the surface state easily changes and hillocks of about 50 nm in size disappear. Further, when an atomic force microscope (AFM) is used, it can be seen that the surface is rough after etching by observing the 5 μm region. A surface in which 60% or more of surface atoms are terminated with N atoms has this property, and in this specification, a surface having such a property is referred to as an N-terminated surface. On the other hand, the surface condition of the Ga termination surface is hardly changed by the same processing method, and even when AFM is used, almost no surface change is observed after etching in the observation of the 5 μm region (for example, Appl. Phys. Lett. 71 , 2635 (1997)). A surface in which 60% or more of surface atoms are terminated with Ga atoms has this property. In this specification, a surface having such a property is referred to as a Ga-terminated surface. Therefore, with respect to III-N compound semiconductors, a surface having 60% or more of the terminal atoms exposed on the surface being N atoms and having the property of being easily roughened by a predetermined etching can be called an N terminal surface. A surface having a property that 60% or more of the terminal atoms exposed to the group III group atoms are difficult to change by a predetermined etching can be called a group III atom terminal surface.
[0016]
In addition to etching, differences in polarity (differences in terminal atoms) can be achieved by the reflection high-energy electron diffraction (RHEED) method (for example, Appl. Phys. Lett. 72, 2114 (1998)), and coaxial direct collision ion scattering. By using spectroscopy (CAICISS), it is possible to discriminate and evaluate nondestructively.
[0017]
Examples of III-N compound semiconductors include GaN, AlN, Al _x Ga _lx N (0 <x <1), InN, In _x Ga _1-x N (0 <x <1), In _x Ga _y Al _1-xy N (0 <x <1, 0 <y <1). In particular, the present invention preferably uses a Ga-containing III-N compound semiconductor, that is, a GaN compound semiconductor.
[0018]
Typically, in the present invention, the concentration of n-type impurities in the semiconductor substrate is 1 × 10 ¹⁷ cm ^-3 ~ 1x10 ^{twenty one} cm ^-3 Is within the range. Preferably, the concentration of the n-type impurity in the semiconductor substrate is 1 × 10 ¹⁷ cm ^-3 ~ 1x10 ¹⁹ cm ^-3 Is within the range. Within these ranges, the concentration of the n-type impurity may be constant or may vary in the direction of the substrate thickness.
[0019]
In the present invention, the concentration of the n-type impurity in the semiconductor substrate may be constant in the thickness direction of the semiconductor substrate or may vary. When the concentration of the n-type impurity changes in the thickness direction, the semiconductor substrate includes a first portion that forms a nitrogen termination surface and has a first n-type impurity concentration, and a first n-type impurity concentration. It is preferable to have at least a second portion having a second n-type impurity concentration lower than the impurity concentration. When the concentration of the n-type impurity changes in the direction of the thickness of the substrate, the first n-type impurity concentration of the first portion is 3 × 10 ¹⁸ cm ^-3 The above is preferable. The thickness of the first portion is preferably 0.05 μm to 50 μm.
[0020]
When the n-type impurity concentration changes in the thickness direction of the substrate, a plurality of semiconductor layers may be formed on the second portion having an n-type impurity concentration lower than the first n-type impurity concentration. preferable. Also in this case, the thickness of the first portion is preferably 0.05 μm to 50 μm. Further, the first n-type impurity concentration of the first portion is 3 × 10 ¹⁸ cm ^-3 The above is preferable.
[0021]
The semiconductor device according to the present invention is typically a light emitting element.
According to the present invention, another semiconductor device is provided. The semiconductor device includes a III-N compound semiconductor substrate, a plurality of III-N compound semiconductor layers formed on the semiconductor substrate, and the semiconductor substrate. An n-type electrode and a p-type electrode for applying a voltage to the plurality of formed semiconductor layers are provided, wherein the semiconductor substrate is p-type, and the uppermost layer of the plurality of semiconductor layers has a nitrogen termination surface. The n-type electrode is formed on the nitrogen termination surface. The III-N compound semiconductor is typically a GaN compound semiconductor. In this case, the p-type electrode is preferably formed on the Ga termination surface of the semiconductor substrate. The semiconductor device according to the present invention is particularly applicable to a light emitting element.
[0022]
According to the present invention, a further semiconductor device is provided, and the semiconductor device is formed on a III-N compound semiconductor substrate, a plurality of III-N compound semiconductor layers formed on the semiconductor substrate, and the semiconductor substrate. An n-type electrode and a p-type electrode for applying a voltage to a plurality of semiconductor layers, wherein the semiconductor substrate is n-type, and the n-type electrode is formed on a nitrogen termination surface of the semiconductor substrate The concentration of the n-type impurity in the semiconductor substrate changes in the thickness direction of the semiconductor substrate, and the semiconductor substrate forms a nitrogen termination surface and has a first average n-type impurity concentration It consists of a first portion and a second portion having a second average n-type impurity concentration lower than the first average n-type impurity concentration, and the first average n-type impurity concentration is 3 × 10 ¹⁸ cm ^-3 The second average n-type impurity concentration is 3 × 10. ¹⁸ cm ^-3 The plurality of semiconductor layers are formed on the second portion. Preferably, the first average n-type impurity concentration is 3 × 10 ¹⁸ cm ^-3 ~ 1x10 ^{twenty one} cm ^-3 Is within the range. Preferably, the second average n-type impurity concentration is 1 × 10 ¹⁷ cm ^-3 ~ 3x10 ¹⁸ cm ^-3 Is within the range. More preferably, the first average n-type impurity concentration is 3 × 10 ¹⁸ cm ^-3 ~ 1x10 ¹⁹ cm ^-3 Is within the range. The III-N compound semiconductor is preferably a GaN compound semiconductor. The semiconductor device according to the present invention is particularly applicable to a light emitting element.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
The impurity concentration in the present invention can be measured using, for example, a SIMS (secondary ion analysis) apparatus. In the present invention, the n-type electrode includes Au or Al, such as Ti / Al, Hf / Au, W / Al, V / Al, and Sc, Y, La, Ti, Zr, Hf, V, Nb, Ta, It can be formed by combining W, Mo, Cr, Mn, Tc, Re or N. Furthermore, other materials may be used as long as the material exhibits good ohmic characteristics with the surface of the n-type III-N compound semiconductor.
[0024]
In the present invention, the impurity concentration in the III-N compound semiconductor substrate is 1 × 10 ¹⁷ cm ^-3 1 × 10 or more ^{twenty one} cm ^-3 The following is preferable, and further 1 × 10 ¹⁷ cm ^-3 1 × 10 or more ¹⁹ cm ^-3 The following is preferred. Si is preferable as the n-type impurity, but other impurities capable of imparting n-type conductivity can also provide the same effect as Si.
[0025]
In the III-N-based compound semiconductor substrate, the thickness of the portion having a high impurity concentration is preferably set to a thickness that does not affect the unevenness of the surface, and is preferably 0.05 μm to 50 μm, for example, 0.05 μm. About 10 to 10 μm is more preferable.
[0026]
In the present invention, the III-N compound semiconductor substrate can be obtained by epitaxially growing a thick film of a III-N compound semiconductor on a seed substrate and separating the obtained thick film from the seed substrate. A sapphire substrate having a (0001) plane can be preferably used as a seed substrate for obtaining a III-N compound semiconductor substrate, particularly a GaN compound semiconductor substrate. Furthermore, a sapphire substrate having another crystal plane, GaN, SiC, spinel, mica, or the like may be used as a seed substrate. Whichever seed substrate is used, the object of the present invention can be achieved.
[0027]
In preparing the GaN-based compound semiconductor substrate, a GaN film can be preferably used as the low-temperature buffer layer formed on the seed substrate. A substrate can be obtained by forming a thick film of a GaN-based compound semiconductor on the low-temperature buffer layer and taking out the thick film by polishing. Furthermore, Al as a low temperature buffer layer _x Ga _1-x N (0.ltoreq.x.ltoreq.1) or ZnO may be used. In either case, the same effect as that obtained when the GaN low-temperature buffer layer is used can be obtained.
[0028]
The thick film in the substrate preparation is preferably grown by the H-VPE method. Lasers fabricated using GaN substrates grown by H-VPE methods have lower thresholds than lasers fabricated using GaN substrates fabricated by sublimation, high pressure synthesis, and other thick film growth methods. Can oscillate at a voltage, lower threshold current. Since HCl is used during growth in the H-VPE method, the grown GaN thick film contains chlorine (Cl), and this Cl forms an intermediate product at the electrode portion to alleviate the electrical barrier. As a result, it is considered that good characteristics are brought about. However, even if another thick film growth method is used instead of the H-VPE method, an effect such as a threshold voltage lower than the conventional one can be obtained.
[0029]
In the present invention, the structure of an element such as a laser can be formed on a III-N compound semiconductor substrate separated from the seed substrate, for example, a GaN substrate. The element structure can be preferably formed by, for example, a metal organic chemical vapor deposition method (MOCVD method). On the other hand, a multi-layered GaN-based compound semiconductor layer including a light emitting layer may be grown by MOCVD on the GaN thick film attached to the seed substrate. Thereafter, the GaN compound semiconductor laser obtained by removing the seed substrate, the underlying undoped GaN film, and the mask by polishing or the like can also exhibit good characteristics as in the case of using the first separated substrate.
[0030]
In the present invention, a GaN substrate can be particularly preferably used, but substrates made of other GaN compound semiconductors and other III-N compound semiconductors can also be used. Furthermore, among the elements constituting the GaN-based compound semiconductor, a part (about 10% or less) of the nitrogen element may be replaced with an element selected from the group consisting of P, As, and Sb. Such materials can also have a similar effect.
[0031]
In the present invention, it is preferable to use a hexagonal substrate grown in the c-axis direction. In this case, the hexagonal C-plane is exposed on the N-termination surface and the Ga-termination surface of the substrate. Such a substrate can be obtained by epitaxial growth on the (0001) plane of the seed substrate. On the other hand, a thick film grown from another crystal plane may be used as the substrate. Such growth includes growth of GaN on the M-plane (01-10) in the <01-13> direction, growth of GaN on the A-plane (2-1-10) in the c-axis direction, Growth of GaN on the R plane (011-2) in the <2-1-10> direction, and growth of GaN on the cubic [(111) plane + slightly inclined plane] in the c-axis direction There is. Even in those cases, an N termination surface for the n-type electrode can be obtained.
[0032]
In the present invention, when a substrate having a C crystal face exposed on the main surface is used, the c-axis of the substrate crystal deviates from 0.10 ° to 0.25 ° with respect to the direction perpendicular to the substrate main surface (crystal stacking direction). It is preferable that it is shifted by 0.15 ° to 0.20 °. In this case, the flatness of the crystal surface grown on the substrate is promoted, the crystallinity of the entire device can be improved, and the characteristics of the active layer and thus the device can be further improved.
[0033]
Further, the MOCVD method is preferably used in order to produce an element structure such as a laser on the substrate. In addition, other epitaxial growth methods such as molecular beam epitaxy (MBE) may be used. Examples of raw materials used in the MOCVD method include trimethylgallium (TMG), trimethylaluminum (TMA), trimethylindium (TMI), NH _Three , And biscyclopentadienyl magnesium (Cp ₂ Mg). Other than these, any materials can be used as long as they can grow necessary compounds. As a dopant for a device structure such as a III-N compound semiconductor substrate, particularly a GaN substrate, and a laser, Si, Ge, Sn, O, S, Se or Te in the case of n type, Mg in the case of p type , Be, Ca, Sr, Ba, Zn or Cd can be used.
[0034]
In addition, the present invention is particularly applied to light emitting elements. The light emitting element includes, for example, a laser and a light emitting diode (LED). In the case of a laser, according to the present invention, a low contact specific resistance, a low threshold voltage, or a low threshold current density can be obtained. In the case of a light emitting diode, according to the present invention, it is possible to realize a reduction in voltage during driving and an improvement in surface flatness.
[0035]
FIG. 1A shows a specific example of a semiconductor device according to the present invention applied as a semiconductor laser. An n-type electrode 101 is formed on one main surface 102 </ b> A of the GaN substrate 102. The main surface 102A in contact with the n-type electrode 101 is an N termination surface. On the other main surface of the GaN substrate 102, an n-type GaN layer 103, an n-type Al _0.1 Ga _0.9 N clad layer 104, n-type GaN light guide layer 105, multiple quantum well light emitting layer 106, p-type Al _0.2 Ga _0.8 N carrier block layer 107, p-type GaN light guide layer 108, p-type Al _0.1 Ga _0.9 An N clad layer 109, a p-type GaN contact layer 110, and a p-type electrode 111 are sequentially formed. Hereinafter, a manufacturing process of this semiconductor laser will be described.
[0036]
Example 1
As shown below, a GaN thick film was grown on a sapphire substrate by the H-VPE method, and the obtained thick film was used as a substrate to prepare a semiconductor laser shown in FIG.
[0037]
First, a sapphire substrate having a (0001) plane is cleaned, and an undoped GaN film having a thickness of about 3 μm is grown as a base layer by MOCVD using the following procedure. The cleaned sapphire substrate is introduced into the MOCVD apparatus, and H ₂ Cleaning is performed at a high temperature of 1100 ° C. in an atmosphere. Thereafter, the temperature is lowered and hydrogen (H ₂ ) At a flow rate of 10 L / min and NH at 600 ° C. _Three And trimethylgallium (TMG) are introduced at 5 L / min and 20 mol / min, respectively, to grow a GaN low-temperature buffer layer having a thickness of about 20 nm.
[0038]
Thereafter, the supply of TMG is once stopped, the temperature is raised again to 1050 ° C., TMG is introduced at about 100 mol / min, and an undoped GaN film having a thickness of 3 μm is grown in one hour. Then TMG and NH _Three Is stopped, the temperature is lowered to room temperature, and the sapphire substrate on which the undoped GaN underlayer is grown is taken out. For the low temperature buffer layer, instead of the GaN film, trimethylaluminum (TMA), TMG, NH _Three May be used to form an AlN film or a GaAlN film.
[0039]
When growing a thick GaN film on the undoped GaN foundation layer (the outermost surface is a Ga termination surface) produced by the above method, the growth is controlled in the form of stripes with a thickness of 2000 mm, a width of 7 μm, and an interval of 10 μm so as not to cause cracks. A film is formed, and selective growth is performed thereon by H-VPE method to grow a flat GaN thick film. In this example, as the growth suppression film, SiO deposited by electron beam evaporation (EB method) is used. ₂ A film etched using photolithography is used. A sapphire substrate having an undoped GaN base film partially covered with a stripe-like growth suppression film is introduced into the H-VPE apparatus. N ₂ Carrier gas and NH _Three The substrate temperature is raised to about 1050 ° C. while flowing 5 L / min. Thereafter, GaCl is introduced at 100 cc / min on the substrate to start the growth of the GaN thick film. GaCl is generated by flowing HCl gas through Ga metal maintained at 850 ° C. In addition, doping can be arbitrarily performed during growth by flowing an impurity gas using an impurity doping line that is individually connected to the vicinity of the substrate. In this example, for the purpose of doping Si, the growth is started and at the same time monosilane (SiH _Four ) 200 nmol / min, Si-doped GaN layer (Si impurity concentration: 3.8 × 10 6) ¹⁸ cm ^-3 ) And a 350 μm thick GaN thick film is obtained after a total growth of 3 hours. The outermost surface of GaN produced under such growth conditions is a Ga termination surface. For Si doping, SiH _Four Not limited to monochlorosilane (SiH _Three Cl), dichlorosilane (SiH ₂ Cl ₂ ), Trichlorosilane (SiHCl _Three Other raw materials such as) may be used.
[0040]
After growth, polished sapphire substrate, undoped GaN film by MOCVD method, SiO ₂ The film is removed, and polishing is performed until an N termination surface appears, thereby obtaining a GaN substrate 102 shown in FIG. The surface on which the GaN substrate is polished is an N termination surface, and the opposite growth top surface is a Ga termination surface.
[0041]
Using the obtained GaN thick film as a substrate, a light emitting device structure is grown by MOCVD as follows. First, the substrate is introduced into the MOCVD apparatus, and N ₂ And NH _Three Each is heated to 1050 ° C. while flowing 5 L / min. If the temperature rises, N ₂ To H ₂ Instead of TMG 100 μmol / min, SiH _Four Is introduced at 10 nmol / min, and the n-type GaN layer 103 shown in FIG. 1 is grown by 4 μm. Thereafter, the flow rate of TMG is adjusted to 50 μmol / min, TMA is introduced at 40 μmol / min, and n-type Al is introduced. _0.1 Ga _0.9 The N clad layer 104 is grown to a thickness of 0.5 μm. Al _0.1 Ga _0.9 When the growth of N is completed, the supply of TMA is stopped, TMG is adjusted to 100 μmol / min, and the n-type GaN light guide layer 105 is grown to a thickness of 0.1 μm. Then TMG, SiH _Four Is stopped and the carrier gas is turned to H ₂ To N ₂ Then, the temperature was lowered to 700 ° C., trimethylindium (TMI) as an indium raw material was introduced at 10 μmol / min, and TMG was introduced at 15 μmol / min. _0.05 Ga _0.95 A 4 nm thick barrier layer of N is grown. Thereafter, the supply amount of TMI is increased to 50 μmol / min. _0.2 Ga _0.8 A 2 nm thick well layer made of N is grown. A total of three well layers are grown by the same method, and a light emitting layer 106 of a multiple quantum well (MQW) in which a total of four barrier layers exist between and on both sides of the well layers is grown. When the growth of MQW is finished, the supply of TMI and TMG is stopped, the temperature is raised again to 1050 ° C., and the carrier gas is again N ₂ To H ₂ In place of TMG 50 μmol / min, TMA 30 μmol / min, P-type doping raw material biscyclopentadienylmagnesium (Cp ₂ Mg) was flowed at 10 nmol / min, and 20 nm thick p-type Al. _0.2 Ga _0.8 An N carrier block layer 107 is grown. When the growth of the carrier block layer is completed, the supply of TMA is stopped, the supply amount of TMG is adjusted to 100 μmol / min, and the p-type GaN light guide layer 108 having a thickness of 0.1 μm is grown. Thereafter, the supply of TMG was adjusted to 50 μmol / min, 40 μmol / min of TMA was introduced, and 0.4 μm thick p-type Al _0.1 Ga _0.9 The N clad layer 109 is grown. Finally, the supply of TMG is adjusted to 100 μmol / min, the supply of TMA is stopped, and the p-type GaN contact layer 110 having a thickness of 0.1 μm is grown. End growth. When growth is complete, TMG and Cp ₂ The supply of Mg is stopped and the temperature is lowered, and the substrate is taken out from the MOCVD apparatus at room temperature.
[0042]
Thereafter, using a dry etching apparatus, the p-GaN contact layer 110 is left in a stripe shape having a width of 5 μm, and p-Al _0.1 Ga _0.9 Etching is performed up to the N light guide layer 109 to form an optical waveguide. Next, P-type electrode 111 is formed by sequentially vapor-depositing 150 Pd and Au 1000 Au on the p-GaN portion. Further, while maintaining the substrate temperature at about 200 ° C., the n-type electrode 101 is formed by sequentially depositing 150 nm of Ti and 1000 mm of Al on the N termination surface 102A of the GaN substrate. Finally, cleaving or dry etching is performed so that the element length is about 1 mm, thereby forming an end face to be a mirror.
[0043]
In the semiconductor laser obtained by the above process, the impurity concentration profile of the GaN substrate is as shown in FIG. In the thickness direction of the n-type GaN substrate 102, the concentration of the n-type impurity (Si) is substantially constant, and 3.8 × 10 ¹⁸ cm ^-3 It is. The laser manufactured in this example has an oscillation threshold voltage of about 5 V and a threshold current density of 1.2 kA / cm. ² It is. The laser was subjected to a life test of about 1000 hours under conditions near the threshold, but no change in characteristics was observed.
[0044]
Comparative Example 1
Each layer was epitaxially grown on the N termination surface of the GaN substrate obtained in Example 1, and an n-type electrode was formed on the Ga termination surface to obtain a laser. FIG. 2A shows a cross-sectional view of the GaN-based compound semiconductor laser produced, and FIG. 2B shows an impurity concentration profile in the growth direction (thickness direction) of the GaN substrate. The laser was prepared according to the following process.
[0045]
Undoped GaN film and SiO by MOCVD method ₂ Formation of the film and growth by the H-VPE method are performed in the same manner as in Example 1. Next, the N termination surface of the GaN substrate is used as an epitaxial growth surface, and thereafter, the n-type GaN layer 203, the n-type Al layer are formed on the GaN substrate 202 in the same manner as in the first embodiment. _0.1 Ga _0.9 N clad layer 204, n-type GaN light guide layer 205, multiple quantum well light emitting layer 206, p-type Al _0.2 Ga _0.8 N carrier block layer 207, p-type GaN light guide layer 208, p-type Al _0.1 Ga _0.9 An N clad layer 209, a p-type GaN contact layer 210, and a p-type electrode 211 are formed, and an n-type electrode 201 is formed on the Ga termination surface 202A.
[0046]
The obtained element did not oscillate at room temperature.
In order to find out the cause of the laser oscillation failure, a GaN substrate was produced in the same manner as in Example 1, and a Ti (150 mm) / Al (1000 mm) electrode having a diameter of 0.5 mm was formed on the N termination surface and the Ga termination surface. Nine pieces of 201 were deposited in sequence at intervals of 1.0 mm, for a total of 18 pieces, and their voltage-current characteristics were examined. FIG. 3 shows an n-type electrode pattern deposited on the N-termination surface or Ga-termination surface of the GaN substrate, 301 is an n-type electrode, and 302 is a GaN substrate. FIG. 4 shows the current-voltage characteristics of the n-type electrode evaporated on the N termination surface of the GaN substrate, and FIG. 5 shows the current-voltage characteristics of the n-type electrode evaporated on the Ga termination surface of the GaN substrate. Show. As shown in FIG. 4, the n-type electrode on the N termination surface exhibits good ohmic characteristics. On the other hand, as shown in FIG. 5, the n-type electrode on the Ga termination surface exhibits Schottky characteristics, suggesting the presence of a barrier layer.
[0047]
C and the like are easily bonded to Ga dangling bonds existing on the Ga termination surface. Therefore, when an electrode such as Ti / Al is formed in the presence of C or the like, a barrier layer is formed, and the obtained electrode can exhibit Schottky characteristics. On the other hand, in the N terminal surface, the probability that atoms forming such a barrier may exist on the surface is low. Therefore, an n-type electrode showing good ohmic characteristics can be formed on the N terminal surface without performing surface treatment or the like.
[0048]
On the other hand, the epitaxial growth of the GaN-based compound semiconductor layer on the Ga termination surface is performed at a high temperature of 1000 ° C. or higher. In this case, it is considered that impurities on the surface are separated and cleaned, and as a result, a good GaN-based compound semiconductor layer can be formed.
[0049]
Example 2
Dopant source SiH _Four The GaN thick films having different impurity concentrations were grown by the H-VPE method with various supply values of 10 nmol / min to 1000 nmol / min. During the growth of each GaN thick film, SiH _Four The flow rate of was constant. Other conditions were the same as in Example 1. Using the obtained GaN thick film as a substrate, a laser was produced in the same manner as in Example 1, and their characteristics were measured. Each layer for the laser was epitaxially grown on the Ga termination surface of the GaN substrate. The n-type electrode was formed on the N termination surface of the GaN substrate.
[0050]
FIG. 6 shows SiH when growing a GaN thick film. _Four It represents the relationship between the supply amount and the concentration of impurities contained in the film. The envelope 7 shows the relationship between the impurity concentration in the GaN substrate and the threshold voltage of a laser manufactured using the GaN substrate. FIG. 8 shows the relationship between the impurity concentration in the GaN substrate and the threshold current density of a laser manufactured using the GaN substrate. FIG. 9 shows the relationship between the impurity concentration in the GaN substrate and the surface roughness of the GaN substrate.
[0051]
As shown in FIG. 6, SiH _Four The supply amount and the impurity concentration in the GaN substrate are proportional to each other, and SiH _Four The impurity concentration when the supply amount is 1000 nmol / min is 1.6 × 10 ¹⁹ cm ^-3 It is. As shown in FIG. 7, as the impurity concentration in the GaN substrate increases, the oscillation threshold voltage of the manufactured laser tends to decrease gradually. This is due to the fact that the resistance of the GaN substrate has decreased due to the influence of impurities, but the Schottky barrier generated at the N termination surface and the n-type electrode contact portion has been further reduced, and the contact specific resistance has decreased. As a result, the threshold voltage is considered to be low. The oscillation threshold voltage is such that the impurity concentration of the GaN substrate is about 1 × 10. ¹⁷ cm ^-3 With the above, it has converged to a value of about 5V.
[0052]
On the other hand, FIG. 8 shows that the impurity concentration of the GaN substrate is about 1 × 10. ¹⁹ cm ^-3 Above this, the oscillation threshold current density of the laser begins to increase gradually, 5 × 10 ^{twenty one} cm ^-3 Above 2 kA / cm ² It has converged to a value of about. This means that, as shown in FIG. 9, the impurity concentration in the GaN substrate is about 1 × 10 5. ¹⁹ cm ^-3 This is probably because the average surface roughness of the film surface has begun to increase from above. That is, when the surface roughness of the film increases, the unevenness at the interface of each layer in the laser structure grown thereon increases, and the dispersion of light in the guide layer that propagates the laser light increases, which is the threshold current density. It is thought that this has led to an increase in
[0053]
In addition, an n-electrode was formed on the N termination surface side of the GaN substrate used for laser fabrication, and the contact specific resistance with respect to the impurity concentration was examined by a Trans Mission Line Model (TLM) method. This is a method for obtaining the contact specific resistance from the inter-electrode distance dependency on the assumption that the measurement sample is uniform in the plane. This time, an electrode pad pattern of Ti (150 Å) / Al (1000 Å), size 300 μm, and interval 10 to 100 μm was used.
[0054]
FIG. 10 shows the relationship between the impurity concentration in the GaN substrate and the contact specific resistance. Impurity concentration is 1 × 10 ¹⁷ cm ^-3 If it exceeds 1, the contact specific resistance is 1 × 10 ^-Five Ω · cm ² After that, the specific resistance decreases as the impurity concentration increases.
[0055]
From the above results, the impurity concentration of the GaN substrate is 1 × 10 5. ¹⁷ cm ^-3 1 × 10 or more ^{twenty one} cm ^-3 Desirably 1x10 ¹⁷ cm ^-3 1 × 10 or more ¹⁹ cm ^-3 The following is more desirable. If the impurity concentration is too low, the resistance of the substrate itself increases, and an intermediate product between the electrode and the GaN substrate is formed, which can make it difficult to reduce the barrier. On the other hand, when the impurity concentration is too high, the growth surface becomes rough, the crystallinity during regrowth is lowered, and the device characteristics can be deteriorated. More preferable characteristics can be obtained by forming an n-type electrode on the N terminal surface of the substrate having an appropriate impurity concentration.
[0056]
Example 3
As shown below, the laser element was prepared by changing the carrier concentration of the GaN substrate in the thickness direction. FIG. 11A shows a cross-sectional view of the manufactured GaN-based compound semiconductor laser, and FIG. 11B shows an impurity concentration profile in the thickness direction of the GaN substrate. The GaN substrate 1002 used here is a Si highly doped GaN layer 1002a (Si impurity concentration: 8.0 × 10 ¹⁸ cm ^-3 ) And a Si-doped GaN layer 1002b (Si impurity concentration: 3.8 × 10 6) ¹⁸ cm ^-3 ). The n-type electrode 1001 is formed on the N termination surface 1002 A of the substrate 1002. The GaN layer 1002a that forms the N termination surface that contacts the n-type electrode 1001 has a higher impurity concentration than the GaN layer 1002b that contacts the laser structure. The manufacturing process is shown below.
[0057]
Undoped GaN film and SiO by MOCVD method ₂ The film is formed in the same manner as in Example 1. Thereafter, growth is performed by the H-VPE method as follows.
[0058]
First, a sapphire substrate on which an undoped GaN base layer having a striped growth suppression film is grown is introduced into an H-VPE apparatus. N ₂ Carrier gas and NH _Three The substrate temperature is raised to 1050 ° C. while flowing 5 L / min. Thereafter, GaCl is introduced at 100 cc / min on the substrate to start the growth of the GaN thick film. GaCl is generated by flowing HCl gas through Ga metal maintained at about 850 ° C. In addition, doping can be arbitrarily performed during growth by flowing an impurity gas using an impurity doping line that is individually connected to the vicinity of the substrate. Growth started while doping Si, monosilane (SiH _Four ) For 3 minutes at 500 nmol / min, Si highly doped GaN layer 1002a (Si impurity concentration: 8.0 × 10 ¹⁸ cm ^-3 ) For 5 μm, and then SiH _Four The flow rate of Si was changed to 200 nmol / min, and the Si normal doped GaN layer 1002b (Si impurity concentration: 3.8 × 10 6 ¹⁸ cm ^-3 ) And a 350 μm thick GaN thick film is obtained after a total growth of 3 hours. The outermost surface (epitaxial surface) of GaN produced under such conditions was a Ga termination surface. For Si doping, SiH _Four Not limited to monochlorosilane (SiH _Three Cl), dichlorosilane (SiH ₂ Cl ₂ ), Trichlorosilane (SiHCl _Three Other raw materials such as) may be used.
[0059]
After growth, polished sapphire substrate, undoped GaN film by MOCVD method, SiO ₂ The film is removed, and polishing is performed until an N termination surface appears, whereby a GaN substrate 1002 is obtained. Using the GaN thick film obtained as described above as a substrate, an epitaxial growth layer is formed on the Ga termination surface opposite to the N termination surface 1002A by using the MOCVD method to obtain a light emitting device structure. In the same manner as in Example 1, the n-type GaN layer 1003, the n-type Al _0.1 Ga _0.9 N clad layer 1004, n-type GaN light guide layer 1005, multiple quantum well light emitting layer 1006, p-type Al _0.2 Ga _0.8 N carrier block layer 1007, p-type GaN light guide layer 1008, p-type Al _0.1 Ga _0.9 An N-cladding layer 1009, a p-type GaN contact layer 1010, and a p-type electrode 1011 are formed, and an n-type electrode 1001) is formed on the N termination surface 1002A of the GaN substrate to obtain an element.
[0060]
The obtained laser has an oscillation threshold voltage of about 5 V and a threshold current density of 1.0 kA / cm. ² Met. A life test of about 1500 hours was performed under conditions near the threshold, but no change in characteristics was observed.
[0061]
Comparative Example 2
A Si highly doped layer was formed on the Ga termination surface side of the GaN substrate, and an n-type electrode was fabricated on the Ga termination surface. On the other hand, an epitaxial growth layer for the laser device structure was formed on the N termination surface of the GaN substrate. FIG. 12A shows a cross-sectional view of the fabricated GaN-based compound semiconductor laser, and FIG. 12B shows an impurity concentration profile in the growth direction (thickness direction) of the GaN substrate. The GaN substrate 1102 includes a Si-normally doped GaN layer 1102a (Si impurity concentration: 3.8 × 10 ¹⁸ cm ^-3 ) And Si highly doped GaN layer 1102b (Si impurity concentration: 8.0 × 10) ¹⁸ cm ^-3 ). The laser structure is formed on the Si highly doped GaN layer 1102b. The n-type electrode 1101 is formed on the Ga termination surface 1102A of the Si normally doped GaN layer 1102a. The manufacturing process is shown below.
[0062]
Undoped GaN film and SiO by MOCVD method ₂ The film is formed in the same manner as in Example 1. A sapphire substrate on which an undoped GaN underlayer having a stripe-like growth suppression film is grown is introduced into the H-VPE apparatus. N ₂ Carrier gas and NH _Three The substrate temperature is raised to 1050 ° C. while flowing 5 L / min. Thereafter, GaCl is introduced at 100 cc / min on the substrate to start the growth of the GaN thick film. GaCl is generated by flowing HCl gas through Ga metal maintained at 850 ° C. In addition, doping can be arbitrarily performed during growth by flowing an impurity gas using an impurity doping line that is individually connected to the vicinity of the substrate.
[0063]
Growth started while doping Si, monosilane (SiH _Four ) Is supplied at 200 nmol / min for about 3 hours to obtain a Si normal doped GaN layer 1102a (Si impurity concentration: 3.8 × 10 6). ¹⁸ cm ^-3 ) To 345 μm, and then SiH _Four The Si flow rate is changed to 500 nmol / min, and the Si highly doped GaN layer 1102b (Si impurity concentration: 8.0 × 10 ¹⁸ cm ^-3 ) For 3 minutes (corresponding to a thickness of about 5 μm) to obtain a thick GaN film of about 350 μm. The outermost surface of GaN produced under such growth conditions is a Ga termination surface.
[0064]
After growth, polished sapphire substrate, undoped GaN film by MOCVD method, SiO ₂ The film is removed and polished until the N terminal surface is obtained, thereby obtaining a GaN substrate 1102. Using the GaN thick film obtained as described above as a substrate, epitaxial growth is formed on the N termination surface by MOCVD to obtain a light emitting device structure. Similar to Example 1, n-type GaN layer 1103, n-type Al _0.1 Ga _0.9 N-cladding layer 1104, n-type GaN light guide layer 1105, multiple quantum well light-emitting layer 1106, p-type Al _0.2 Ga _0.8 N carrier block layer 1107, p-type light guide layer 1108, p-type Al _0.1 Ga _0.9 An N-cladding layer 1109, a p-type GaN contact layer 1110, and a p-type electrode 1111 are formed, and an n-type electrode 1101 is formed on the Ga termination surface 1102A to obtain a laser element.
[0065]
The obtained laser did not oscillate continuously at room temperature.
Ti / Al n-type electrodes were formed on the N-termination surface and Ga-termination surface of the fabricated GaN substrate, respectively, and their characteristics were examined. As a result, the n-type electrode on the N termination surface showed good ohmic characteristics, but the n-type electrode on the Ga termination surface showed Schottky characteristics, suggesting the presence of a barrier layer.
[0066]
On the other hand, even when the n-type electrode (101 in FIG. 1A) is formed on the N termination surface of the Si normal doped layer, the n-type electrode (1001 in FIG. 11A) is formed on the N termination surface of the Si highly doped layer. Even when formed, good ohmic characteristics are obtained, and both exhibit excellent electrode characteristics. On the other hand, the contact specific resistance of the n-type electrode 101 is 3 × 10. ^-6 Ω · cm ² In the case of the n-type electrode 1001, 9 × 10 ^-7 Ω · cm ² Met. Therefore, it is preferable to form an n-type electrode on the N termination surface of the Si highly doped layer because the contact specific resistance is reduced.
[0067]
Further, instead of the undoped GaN film formed by the MOCVD method, an impurity concentration of 8 × 10 ¹⁸ cm ^-3 A Si highly doped layer having a concentration of about 2 × 10 is formed on the Si highly doped layer. ¹⁸ cm ^-3 A GaN film was formed. Then, it grind | polished until the N termination | terminus surface of GaN was obtained, and produced the n-type electrode in the N termination | terminus surface of a highly Si doped GaN layer. A laser device obtained using such a process also has an oscillation threshold voltage of about 5 V and a threshold current density of 1.1 kA / cm. ² Met. It is considered that an electrode having good characteristics is formed even in a highly doped region having a relatively large number of defects such as dislocations.
[0068]
Example 4
A laser was fabricated using a GaN substrate in which the impurity doping amount was changed in the film thickness direction. FIGS. 13 (a), 14 (a), 15 (a), 16 (a), 17 (a), and 18 (a) change the impurity concentration used in this example, respectively. FIG. 13 (b), FIG. 14 (b), FIG. 15 (b), FIG. 16 (b), FIG. 17 (b), and FIG. An impurity concentration profile in the thickness direction is shown.
[0069]
The number 1302 in FIG. 13A represents the GaN substrate (where the impurity concentration decreases in the element growth direction (thickness direction)), and the number 1302A represents the N termination surface. The n electrode (not shown) is in contact with the N termination surface. As shown in FIG. 13B, the impurity concentration in the substrate 1302 decreases linearly from the N termination surface toward the epitaxial growth surface for the laser.
[0070]
As shown in FIGS. 14A and 14B, the GaN substrate 1402 includes a first GaN layer 1402a having the highest and constant impurity concentration, and a second GaN in which the impurity concentration decreases linearly in the element growth direction (thickness direction). A layer 1402b and a third GaN layer 1402c having the lowest and constant impurity concentration are included. N termination surface 1402A is in contact with an n-type electrode (not shown).
[0071]
As shown in FIGS. 15A and 15B, the GaN substrate 1502 includes a first GaN layer 1502a in which the impurity concentration decreases linearly in the thickness direction from the highest impurity concentration, a second GaN layer 1502b in which the impurity concentration is constant, and A third GaN layer 1502c in which the impurity concentration decreases linearly to the minimum in the thickness direction is provided. The n-type electrode (not shown) is in contact with the N termination surface 1502A.
[0072]
As shown in FIGS. 16A and 16B, the GaN substrate 1602 includes a first GaN layer 1602a having the highest and constant impurity concentration, a second GaN layer 1602b in which the impurity concentration decreases in the thickness direction, and the highest impurity concentration. The third GaN layer 1602c is low and constant. The n electrode (not shown) is in contact with the N termination surface 1602A.
[0073]
As shown in FIGS. 17A and 17B, in the GaN substrate 1702, the impurity concentration decreases in the thickness direction. The n-type electrode (not shown) is in contact with the N termination surface 1702A.
[0074]
As shown in FIGS. 18A and 18B, in the GaN substrate 1802, the impurity concentration decreases in the thickness direction. The n-type electrode (not shown) is in contact with the N termination surface 1802A.
[0075]
Using GaN substrates each having a concentration distribution as shown in FIG. 13B, FIG. 14B, FIG. 15B, FIG. 16B, FIG. 17B, and FIG. A laser element was fabricated in the same manner as in Example 1. As a result, lasers with good characteristics were obtained, and these characteristics greatly depended on the impurity concentration in the vicinity of the n-type electrode as shown in FIG. Also in this example, good laser characteristics were obtained by forming an n-type electrode on the N termination surface in which 60% or more of the termination atoms appearing on the surface are N atoms.
[0076]
Example 5
In this example, a plurality of regions having different impurity concentrations were provided in the GaN substrate.
[0077]
First, a GaN substrate as shown in FIG. 19 (a) was used. The substrate 1902 has an impurity concentration profile as shown in FIG. A GaN substrate 1902 having an N termination surface 1902A has a Si highly doped layer 1902a (Si impurity concentration: 8.0 × 10 5) having a thickness of about 5 μm. ¹⁸ cm ^-3 ), Si doped layer 1902b (Si impurity concentration: 4.2 × 10 ¹⁸ cm ^-3 Si highly doped layer 1902c (Si impurity concentration: 8.0 × 10 ¹⁸ cm ^-3 ), Si doped layer 1902d (Si impurity concentration: 4.2 × 10 ¹⁸ cm ^-3 ) And Si highly doped layer 1902e (Si impurity concentration: 8.0 × 10 ¹⁸ cm ^-3 ).
[0078]
In the preparation of the GaN substrate, high impurities are formed in at least two locations on the N termination surface side (Si highly doped layer 1902a) and the Ga termination surface side (Si highly doped layer 1902e) by the H-VPE method. An area was established. The Si concentration was constant in each layer of the GaN substrate. Epitaxial growth is performed on the Ga termination surface in the same manner as in Example 3, and the n-type GaN layer, n-type Al _0.1 Ga _0.9 N clad layer, n-type GaN light guide layer, multiple quantum well light emitting layer, p-type Al _0.2 Ga _0.8 N carrier block layer, p-type light guide layer, p-type Al _0.1 Ga _0.9 An N clad layer, a p-type GaN contact layer, and a p-type electrode were formed, and an n-type electrode was formed on the N termination surface to obtain a semiconductor device. The obtained laser has a threshold voltage of about 5 V and a threshold current density of about 1 kA / cm. ² It oscillated at and showed long life characteristics.
[0079]
Ti / Al n-type electrodes were formed on the N termination surface and Ga termination surface of the fabricated GaN substrate, and the characteristics were examined. As a result, the n-type electrode on the N termination surface exhibited good ohmic characteristics, while on the Ga termination surface exhibited Schottky characteristics, indicating the presence of a barrier layer.
[0080]
Furthermore, a semiconductor laser was fabricated using each of the GaN substrates shown in FIGS. 20 (a), 21 (a), and 22 (a). FIGS. 20B, 21B, and 22B show impurity concentration profiles in the thickness direction of the used GaN substrate, respectively.
[0081]
A GaN substrate 2002 shown in FIG. 20A includes a first GaN layer 2002a having a constant impurity concentration, a second GaN layer 2002b having a constant impurity concentration lower than the first GaN layer 2002a, and a higher impurity concentration than the second GaN layer 2002b. A third GaN layer 2002c having a constant impurity concentration lower than that of the third GaN layer 2002c, and a fifth GaN layer 2002e having a constant impurity concentration higher than that of the fourth GaN layer 2002d. The first GaN layer 2002a forms an N termination surface 2002A. The relationship between the impurity concentrations is as shown in Equation (1).
[0082]
Fifth GaN layer 2002e> first GaN layer 2002a> third GaN layer 2002c> second GaN layer 2002b = fourth GaN layer 2002d (Formula 1)
A GaN substrate 2102 shown in FIG. 21A includes a first GaN layer 2102a having a constant impurity concentration, a second GaN layer 2102b having a constant impurity concentration, a third GaN layer 2102c having a constant impurity concentration, a fourth GaN layer 2102d having a constant impurity concentration, and impurities. The fifth GaN layer 2102e has a constant concentration. The first GaN layer 2102a forms an N termination surface 2102A. The relationship between the impurity concentrations is as shown in (Formula 2).
[0083]
Fifth GaN layer 2102e> first GaN layer 2102a> second GaN layer 2002b = fourth GaN layer 2002d> third GaN layer 2002c (Formula 2)
A GaN substrate 2202 shown in FIG. 22A includes a first GaN layer 2202a having a constant impurity concentration, a second GaN layer 2202b having an impurity concentration increasing in the element growth direction (thickness direction), a third GaN layer 2202c having a constant impurity concentration, and element growth. The fourth GaN layer 2202d has an impurity concentration that increases in the direction (thickness direction), and the fifth GaN layer 2202e has a constant impurity concentration. The first GaN layer 2202a forms an N termination surface 2202A. The relationship between the impurity concentrations is as shown in (Equation 3).
[0084]
First GaN layer 2202a> third GaN layer 2202c> fifth GaN layer 2202e (Formula 3)
A laser device was fabricated in the same manner as in Example 1 by using GaN substrates each having the impurity concentration distribution shown in FIGS. 20B, 21B, and 22B. The obtained laser device showed good characteristics. The substrate used in this example includes three Si highly doped layers. However, if the substrate has Si highly doped layers on both end faces, the same effects as in this example can be obtained. Therefore, the Si highly doped layer may be two layers or four or more layers. In the GaN substrate, it is preferable that the portion forming the N termination surface to be in contact with the n-type electrode has a higher n-type impurity concentration than the other portions, but it is necessary to have the highest impurity concentration. Absent. In order to obtain preferable characteristics, it is sufficient that there is at least one portion in the substrate having a lower impurity concentration than the portion forming the N termination surface. A laser element having desirable characteristics can be obtained by forming an n-type electrode on an N termination surface having an appropriately high impurity concentration.
[0085]
Example 6
In this example, when growing a GaN substrate exhibiting n-type conductivity, Ge was used as an impurity in a portion forming the N termination surface of the GaN substrate.
[0086]
First, as in Example 1, the growth of the GaN thick film is started by the H-VPE method, and at the same time, SiH _Four And a predetermined amount of germanium (Ge) were introduced, and an n-type GaN thick film having a predetermined impurity concentration distribution with a total thickness of 350 μm was produced. After growth, polished sapphire substrate, undoped GaN film by MOCVD method, SiO ₂ The film was removed, and polishing was performed until an N termination surface appeared to obtain a GaN substrate. Using this substrate, similarly to Example 1, a laser structure and a p-electrode were formed on the Ga termination surface side, and an n-type electrode was formed on the N termination surface to obtain a laser. The obtained laser oscillated continuously at room temperature. The threshold voltage and threshold current density are about 6V and 1.8 kA / cm, respectively. ² It was about.
[0087]
Comparative Example 3
Similar to Example 6, a GaN thick film was grown by the H-VPE method. During the growth of GaN thick film, SiH _Four And a predetermined amount of germanium (Ge) were introduced, and an n-type GaN thick film having a predetermined impurity concentration distribution with a total thickness of 350 μm was produced. In the thick film formation, a highly doped layer of Si and Ge was formed on the Ga termination surface side. Polishing was performed in the same manner as in Example 6 to obtain a GaN substrate. An n-type electrode was formed on the Ga termination surface of the obtained GaN substrate, and a device structure was epitaxially grown on the N termination surface of the GaN substrate to obtain a laser. The obtained laser structure did not oscillate continuously at room temperature. This was thought to be because the electrode had Schottky characteristics due to the presence of the barrier layer, as in Comparative Example 1.
[0088]
Example 7
The impurity concentration was varied as in Example 3. While starting the growth of GaN thick film by H-VPE method, _Four Was introduced in a predetermined amount, and Ge was further introduced for 3 minutes from the start of growth. Thus, after forming the first region having a high impurity concentration containing Si and Ge, the supply of Ge is stopped, and SiH _Four A second region having a lower impurity concentration than the first region was formed by introducing only a predetermined amount. An n-type GaN thick film having a predetermined impurity concentration distribution with a total thickness of 350 μm was produced. Thereafter, the GaN substrate obtained by polishing was introduced into an MOCVD apparatus, and similarly to Example 3, epitaxial growth was performed on the Ga termination surface side, an n-type electrode was formed on the N termination surface, and a laser element was fabricated. The relationship between the impurity concentration of the first region and the second region of the GaN substrate is first region> second region.
[0089]
The laser device thus obtained has a threshold voltage and a threshold current density of about 5 V and 1.0 kA / cm, respectively. ² The value was low. Thus, it can be seen that not only Si but also Ge can be used as the n-type impurity. O can also be used as an n-type impurity, and the actual effect has been confirmed. Specifically, in the H-VPE method, the amount of O contained in HCl gas can be adjusted, or O can be introduced into the film by flowing oxygen gas during GaN growth.
[0090]
Example 8
In this example, the GaN growth surface was changed to an N termination surface by molecular beam epitaxy (MBE), and an n-type electrode was formed thereon. The structure of the laser device according to this example is shown in FIG. A p-type electrode 2401 is formed on one main surface 2402A of the GaN substrate 2402. A main surface 2402A in contact with the p-type electrode 2401 is a Ga terminal surface. On the other main surface of the GaN substrate 2402, a p-type GaN layer 2403, a p-type Al _0.1 Ga _0.9 N clad layer 2404, p-type GaN light guide layer 2405, multiple quantum well light emitting layer 2406, n-type Al _0.2 Ga _0.8 N carrier block layer 2407, n-type GaN light guide layer 2408, n-type Al _0.1 Ga _0.9 An N clad layer 2409, an n-type GaN contact layer 2410, and an n-type electrode 2411 are formed in this order. The n-type GaN contact layer 2410, which is the uppermost layer of the GaN-based semiconductor layer, has an N termination surface 2410A, and an n-type electrode 2411 is formed thereon. Hereinafter, a manufacturing process of this semiconductor laser will be described.
[0091]
First, as in Example 1, an undoped GaN film having a thickness of 3 μm is grown by MOCVD on a cleaned sapphire substrate having a (0001) plane, and a stripe-like growth suppression film is formed thereon. Next, a sapphire substrate having an undoped GaN base film partially covered with a stripe-like growth suppression film is introduced into the H-VPE apparatus. N ₂ Carrier gas and NH _Three The substrate temperature is raised to about 1050 ° C. while flowing 5 L / min. Thereafter, GaCl is introduced at 100 cc / min on the substrate to start the growth of the GaN thick film. GaCl is generated by flowing HCl gas through Ga metal maintained at 850 ° C. In addition, doping can be arbitrarily performed during growth by flowing an impurity gas using an impurity doping line that is individually connected to the vicinity of the substrate. At the same time as starting the growth of GaN, Cp ₂ Mg was supplied at 90 nmol / min, and an Mg-doped GaN layer (Mg impurity concentration: 9.5 × 10 ¹⁸ cm ^-3 ) And a 350 μm thick GaN thick film is obtained after a total growth of 3 hours. The outermost surface of GaN produced under such growth conditions is a Ga termination surface.
[0092]
After growth, polished sapphire substrate, undoped GaN film by MOCVD method, SiO ₂ The film is removed, and polishing is performed until an N termination surface comes out to obtain a GaN substrate. A light emitting element structure is grown on the obtained substrate by MOCVD as follows. First, the substrate is introduced into the MOCVD apparatus, and N ₂ And NH _Three Each is heated to 1050 ° C. while flowing 5 L / min. If the temperature rises, N ₂ To H ₂ Instead of TMG 100 μmol / min, Cp ₂ Mg is introduced at 10 nmol / min to grow a p-type GaN layer by 4 μm. Thereafter, the flow rate of TMG is adjusted to 50 μmol / min, TMA is introduced at 40 μmol / min, and p-type Al is introduced. _0.1 Ga _0.9 An N clad layer is grown to a thickness of 0.5 μm. Al _0.1 Ga _0.9 When the growth of N is completed, the supply of TMA is stopped, TMG is adjusted to 100 μmol / min, and the p-type GaN light guide layer is grown to a thickness of 0.1 μm. Then TMG, Cp ₂ Stop supply of Mg and change carrier gas to H ₂ To N ₂ Then, the temperature was lowered to 700 ° C., trimethylindium (TMI) as an indium raw material was introduced at 10 μmol / min, and TMG was introduced at 15 μmol / min. _0.05 Ga _0.95 A 4 nm thick barrier layer of N is grown. Thereafter, the supply amount of TMI is increased to 50 μmol / min. _0.2 Ga _0.8 A 2 nm thick well layer made of N is grown. A total of three well layers are grown by the same method, and a light emitting layer of a multiple quantum well (MQW) in which a total of four barrier layers exist between and on both sides of the well layers is grown. When the growth of MQW is finished, the supply of TMI and TMG is stopped, the temperature is raised again to 1050 ° C., and the carrier gas is again N ₂ To H ₂ Instead of SiH, which is an n-type doping raw material, TMG is 50 μmol / min, TMA is 30 μmol / min. _Four At a flow rate of 3 nmol / min and 20 nm thick n-type Al _0.2 Ga _0.8 An N carrier block layer is grown. When the growth of the carrier block layer is completed, the supply of TMA is stopped, the supply amount of TMG is adjusted to 100 μmol / min, and an n-type GaN light guide layer having a thickness of 0.1 μm is grown. Thereafter, the supply of TMG was adjusted to 50 μmol / min, 40 μmol / min of TMA was introduced, and 0.4 μm thick n-type Al _0.1 Ga _0.9 The N clad layer is grown. Finally, the supply of TMG is adjusted to 100 μmol / min, the supply of TMA is stopped, and the n-type GaN contact layer 110 having a thickness of 0.1 μm is grown to grow the light emitting device structure. Exit. When growth is complete, TMG and SiH _Four Is stopped, the temperature is lowered, and the substrate is taken out from the MOCVD apparatus at room temperature.
[0093]
Next, the GaN substrate is introduced into the MBE apparatus, and the temperature of the substrate is raised to 600 ° C. High frequency (RF) excitation N that becomes N source ₂ The Ga cell temperature (around 910 ° C.) and the Si cell temperature are adjusted so that the plasma output is 350 W, the flow rate is 3 cc / min, and the RHEED pattern in the <11-20> direction is streak-like. Then, the N / Ga ratio is increased, GaN is grown under N-rich conditions, and a Si-doped GaN layer having an N termination surface is grown. RHEED observation shows a 1 × 1 pattern at 300 ° C. or higher, and if it changes to a 3 × 3 pattern at around 250 ° C. or a 6 × 6 pattern at 200 ° C., it can be determined that the growth surface is an N-terminated surface. . Thereafter, an n-type electrode is formed on the obtained N termination surface. Further, the ground surface of the polished GaN substrate is further polished until the N termination surface appears to expose the Ga termination surface. A p-type electrode is formed on the obtained new base surface.
[0094]
The laser device thus obtained had an oscillation threshold voltage of 4.8V. Thus, it has been found that an electrode having good characteristics can be formed by forming the n-type electrode on the N termination surface of the GaN layer according to the present invention other than the substrate. Also in this example, the effect of forming an n-type electrode on the N termination surface, in which 60% or more of the termination atoms appearing on the surface are N atoms, appears.
[0095]
Instead, the polarity can be controlled by performing operations such as nitriding of the substrate and annealing of the buffer layer by the H-VPE method, the MOCVD method, or the MBE method. In this case as well, the contact specific resistance of the n-electrode formed on the N terminal surface can be reduced as described above.
[0096]
FIG. 25 shows a preferable impurity concentration in the substrate used in the present invention. In the present invention, the preferred impurity concentration in the substrate is within the first region (1 × 10 ¹⁷ cm ^-3 1 × 10 or more ^{twenty one} cm ^-3 The following). In this range, a low contact specific resistance, a low threshold voltage, and a low threshold current density can be obtained. The second region has a more preferable impurity concentration range (1 × 10 ¹⁷ cm ^-3 1 × 10 or more ¹⁹ cm ^-3 The following). The reason why the second region is preferable to the first region can be understood by referring to the relationship between the impurity concentration and the threshold current density shown in FIG. Referring to FIG. 8, the impurity concentration of the first region is 1 × 10. ^{twenty one} cm ^-3 Although the threshold current density is certainly reduced in the following, the impurity concentration of the second region, that is, 1 × 10 ¹⁹ cm ^-3 The threshold current density is even lower if it is below. The I region and the II region shown in FIG. 25 are impurity concentration ranges obtained by dividing the first region into two. Area I is 3 × 10 ¹⁸ cm ^-3 1 × 10 or more ^{twenty one} cm ^-3 Hereinafter, the second region is 1 × 10 ¹⁷ cm ^-3 3 × 10 or more ¹⁸ cm ^-3 The impurity concentration range is as follows. In the present invention, the nitride semiconductor substrate preferably comprises a first portion having an average impurity concentration in the I region and a second portion having an average impurity concentration in the II region. The first portion preferably forms an N termination surface, and the n-type electrode is preferably formed on the N termination surface of the first portion. In addition, it is preferable to form an epitaxial layer for a semiconductor element such as a light emitting element on the second portion. Hereinafter, the reason and significance of dividing the nitride substrate into the first portion and the second portion having different impurity concentrations will be described.
[0097]
Referring to the relationship between the impurity concentration and the contact specific resistance shown in FIG. 10, the impurity concentration is 1 × 10. ¹⁷ cm ^-3 When the contact specific resistance is 1 × 10 ^-Five Ω · cm ² Furthermore, the impurity concentration is 3 × 10 ¹⁸ cm ^-3 Above that, the contact specific resistance is about 5 × 10 ^-7 ~ 1x10 ^-6 Ω · cm ² Is getting lower. However, referring to the relationship between the impurity concentration and the threshold voltage shown in FIG. ¹⁷ cm ^-3 Above, no change is seen in the threshold voltage, and the impurity concentration is 1 × 10. ¹⁷ cm ^-3 But 3x10 ¹⁸ cm ^-3 But the threshold voltage was almost the same. That is, it is considered that the contact specific resistance reduction effect seen in FIG. 10 was not reflected in the threshold voltage of FIG. The impurity concentration is set to 3 × 10 in order to form an intermediate product between the n-type electrode and the nitride semiconductor substrate (N termination surface) to obtain a low contact specific resistance. ¹⁸ cm ^-3 It is preferable to make it above (FIG. 10). On the other hand, high-concentration impurities (3 × 10 5) in the entire nitride semiconductor substrate. ¹⁸ cm ^-3 When the above is added, the electrical resistance increases due to the deterioration of crystallinity. As a result, it is considered that the effect of the low contact specific resistance shown in FIG. 10 is not reflected in the low threshold voltage. 3 × 10 ¹⁸ cm ^-3 When impurities are added to the nitride semiconductor substrate as described above, the impurity concentration is 5 × 10 5 from the relationship between the impurity concentration and the threshold current density shown in FIG. ¹⁸ cm ^-3 Until the threshold current density is about 1 kA / cm ² However, the impurity concentration is 1 × 10 ¹⁹ cm ^-3 It can be seen that the threshold current value starts to increase when the above is reached (the same applies to the relationship between the impurity concentration and the surface roughness in FIG. 9). If the impurity concentration is increased in this way, the contact specific resistance decreases, but the threshold current increases conversely.
[0098]
The present inventors have found that this dilemma can be solved by configuring the nitride semiconductor substrate with two or more layers having different impurity concentrations. Specifically, the n-type nitride substrate is composed of a first layer having an N termination surface to be in contact with the n-type electrode, and a second layer on which an element structure is to be formed. The average impurity concentration of the first layer is made lower than the average impurity concentration of the first layer. Further, the average impurity concentration of the first layer is 3 × 10. ¹⁸ cm ^-3 This can be done. Although there is no restriction | limiting in particular about the range of the average impurity concentration of a 1st layer, if it presumes from the result of FIG. ¹⁸ cm ^-3 ~ 1x10 ^{twenty one} cm ^-3 Is preferred, 3 × 10 ¹⁸ cm ^-3 ~ 1x10 ¹⁹ cm ^-3 Is more preferable. The average impurity concentration of the second layer is 3 × 10 ¹⁸ cm ^-3 It can be as follows. The range of the average impurity concentration of the second layer is not particularly limited, but when estimated from the results of FIG. 7 and FIG. ¹⁷ cm ^-3 ~ 3x10 ¹⁸ cm ^-3 Is preferred. Here, the average impurity concentration is defined as a value obtained by dividing the total impurity concentration added to a certain layer by the layer thickness. Preferably, in the nitride semiconductor substrate, the second layer is a portion other than the first layer.
[0099]
The thickness of the first layer can be 0.05 μm or more and 50 μm or less, and preferably 0.05 μm or more and 10 μm or less. If the thickness of the first layer is less than 0.05 μm, an intermediate product due to the addition of impurities is not sufficiently formed, and the contact specific resistance can be increased. On the other hand, when the thickness of the first layer exceeds 50 μm, the surface roughness due to the addition of impurities increases (see FIG. 9), which increases the loss due to the optical waveguide and increases the threshold current density. An increase can be encouraged (see FIG. 8). By setting the thickness of the first layer to 50 μm or less, preferably 10 μm or less, the value of the threshold current density can be made smaller than the value shown in FIG.
[0100]
In the present invention, Si, O, Cl, S, Se, or Te can be preferably used as the n-type impurity. In particular, when Si, O, or Cl is used, an n-type nitride semiconductor substrate can be easily obtained. A plurality of types of the impurities may be simultaneously added to the nitride semiconductor substrate. The average impurity concentration of all added impurities is 3 × 10 3 in the first layer. ¹⁸ cm ^-3 1 × 10 or more ^{twenty one} cm ^-3 Or less, preferably 3 × 10 ¹⁸ cm ^-3 1 × 10 or more ¹⁹ cm ^-3 Hereinafter, in the second layer, 1 × 10 ¹⁷ cm ^-3 3 × 10 or more ¹⁸ cm ^-3 It can be as follows. Hereinafter, the present invention will be described in more detail with reference to examples.
[0101]
Example 9
As shown in FIG. 26, the nitride semiconductor light emitting device (laser diode device) according to this example includes an n-type electrode 3001, a nitride semiconductor substrate (for example, a GaN substrate) 3002, an n-type GaN layer 3003, and an n-type Al. _0.1 Ga _0.9 N-cladding layer 3004, n-type GaN light guide layer 3005, multiple quantum well light emitting layer 3006, p-type Al _0.2 Ga _0.8 N carrier block layer 3007, p-type GaN light guide layer 3008, p-type Al _0.1 Ga _0.9 The N-cladding layer 3009, the p-type GaN contact layer 3010, and the p-type electrode 3011 are comprised. The substrate 3002 includes a highly doped GaN layer 3002a (its average impurity concentration range is in the I region shown in FIG. 25) and a low doped GaN layer 3002b (its average impurity concentration range is in the II region shown in FIG. 25). Become. The n-type electrode 3001 is formed on the N termination surface 3002A of the substrate 3002. The average impurity concentration is a value obtained by dividing the total impurity concentration added to the layer by the layer thickness.
[0102]
The feature of this embodiment is that the average impurity concentrations of the highly doped GaN layer 3002a and the lightly doped GaN layer 3002b constituting the nitride semiconductor substrate 3002 belong to the I region and the II region shown in FIG. 25, respectively. That is, the n-type electrode is in contact with the N termination surface 3002A of the highly doped GaN layer 3002a, and the light emitting element structure is in contact with the lowly doped GaN layer 3002b.
[0103]
3 × 10 ¹⁸ cm ^-3 The highly doped GaN layer 3002a having the above average impurity concentration can form a sufficient intermediate product, and as a result, the contact specific resistance between the highly doped GaN layer 3002a and the n-type electrode 3001 becomes small. Meanwhile, 3 × 10 ¹⁸ cm ^-3 By forming a light emitting device structure on a lightly doped GaN layer 3002b having the following average impurity concentration, a low threshold current density and a low threshold voltage can be provided.
[0104]
The laser element according to the present example has the threshold values (for example, threshold voltage 5 V, threshold current density 1.2 kA / cm) of Examples 1 to 8. ² ) Lower threshold current density (0.8 kA / cm) ² ) And a low threshold voltage (4.4V).
[0105]
Example 10
This example is the same as Example 9 except that the nitrogen compound semiconductor substrate is composed of four regions having different impurity concentrations. FIG. 27 shows the impurity concentration distribution of the nitrogen compound semiconductor substrate. These four regions are referred to as an A region, a B region, a C region, and a D region in order from the surface side on which the n-type electrode is formed. An n-type electrode (not shown) is in contact with the A region. The surface of the A region in contact with the n-type electrode is an N termination surface. Here, the average impurity concentration of the A region and the B region is in the I region shown in FIG. 25, and the average impurity concentration of the C region and the D region is in the II region shown in FIG.
[0106]
The light-emitting element using this nitrogen compound semiconductor substrate brought the same effect as in Example 9.
[0107]
Example 11
This example is the same as Example 9 except that a nitrogen compound semiconductor substrate whose impurity concentration continuously changes in the thickness direction is used. FIG. 28 shows an impurity concentration distribution that continuously changes in the nitrogen compound semiconductor substrate. The continuous impurity concentration profile shown in FIG. 28 can be divided into two regions. These regions are referred to as an A region and a B region in this order from the surface side on which the n-type electrode is formed. An n-type electrode is formed in contact with the A region. The surface of the A region in contact with the n-type electrode is an N termination surface. The average impurity concentration of the A region is in the I region shown in FIG. 25, and the average impurity concentration of the B region is in the II region shown in FIG.
[0108]
The light-emitting element using this nitrogen compound semiconductor substrate brought the same effect as in Example 9.
[0109]
Example 12
This example is the same as Example 9 except that the nitrogen compound semiconductor substrate is composed of five regions having different impurity concentrations as shown in FIG. FIG. 29 shows an impurity concentration distribution in the used nitrogen compound semiconductor substrate. These impurity concentration regions are referred to as an A region, a B region, a C region, a D region, and an E region from the side on which the n-type electrode is formed. An n-type electrode (not shown) is formed so as to be in contact with the N termination surface of the A region. The impurity concentrations of the A region, the B region, and the D region correspond to the I region shown in FIG. The impurity concentrations in the C region and the E region correspond to the II region shown in FIG.
[0110]
The total thickness of the A region and the B region is 50 μm. Further, the average impurity concentration of the A region and the B region is in the I region shown in FIG. Thus, the combined portion of the A region and the B region brings about an effect of reducing the contact specific resistance. On the other hand, the C region (layer thickness 30 μm, impurity concentration 2 × 10 ¹⁸ cm ^-3 ), D region (layer thickness 20 μm, impurity concentration 5 × 10 ¹⁸ cm ^-3 ) And E region (layer thickness 60 μm, impurity concentration 1 × 10 ¹⁸ cm ^-3 The average impurity concentration of the combined portion is 2 × 10 from the impurity concentration of each region and the sum of their layer thicknesses. ¹⁸ cm ^-3 Can be estimated. This value belongs to the area II shown in FIG. Thus, the combined portion of the C region, the D region, and the E region has an effect of reducing the threshold voltage and the threshold current density.
[0111]
The light-emitting element using this nitrogen compound semiconductor substrate brought the same effect as in Example 9.
[0112]
As described above, the impurity concentration may change in each of the first region in contact with the n-type electrode and the second region in contact with the element structure of the nitride semiconductor substrate. Further, the average impurity concentration of the first region is 3 × 10. ¹⁸ cm ^-3 If it is above, 3 × 10 in the first region ¹⁸ cm ^-3 There may be portions having a lower impurity concentration. Furthermore, the average impurity concentration of the second region is 3 × 10 ¹⁸ cm ^-3 3 × 10 in the second region if ¹⁸ cm ^-3 There may be portions having higher impurity concentrations. Regarding a region where a plurality of portions having different impurity concentrations are combined, a region having a total film thickness of 50 μm or less and an average impurity concentration belonging to the I region shown in FIG. 25 can effectively reduce the contact specific resistance. Can do. On the other hand, with respect to a region where a plurality of portions having different impurity concentrations are combined, a region whose average impurity concentration belongs to the region II shown in FIG. 25 can effectively reduce the threshold voltage and the threshold current density.
[0113]
Although the semiconductor laser diode element has been described with reference to the first to twelfth embodiments, the present invention can also be applied to a light emitting diode element. When the present invention is applied to a light emitting diode element, it is possible to effectively prevent low color specific resistance due to low contact specific resistance, low operating voltage, reduction of surface roughness, or improvement of light emission intensity.
[0114]
【The invention's effect】
As described above, according to the present invention, a nitride semiconductor device having a low threshold voltage and threshold current density and a long lifetime, particularly a GaN-based compound semiconductor light-emitting device, can be supplied with a high yield.
[Brief description of the drawings]
FIGS. 1A and 1B are a cross-sectional view of a semiconductor laser manufactured in Example 1 and an impurity concentration profile in a substrate thickness direction.
2A and 2B are a cross-sectional view of a semiconductor laser fabricated in Comparative Example 1 and a diagram showing an impurity concentration profile in the substrate thickness direction.
FIG. 3 is a plan view showing a pattern of an n-type electrode deposited on an N termination surface or a Ga termination surface of a GaN substrate.
FIG. 4 is a diagram showing current-voltage characteristics of an n-type electrode deposited on an N termination surface of a GaN substrate.
FIG. 5 is a diagram showing current-voltage characteristics of an n-type electrode deposited on a Ga termination surface of a GaN substrate.
FIG. 6 shows SiH when growing a GaN thick film. _Four It is a figure which shows the relationship between the supply amount and the impurity concentration contained in the film | membrane formed.
FIG. 7 is a diagram showing a relationship between an impurity concentration in a GaN substrate and a threshold voltage of a laser using the GaN substrate.
FIG. 8 is a diagram showing a relationship between an impurity concentration in a GaN substrate and a threshold current density of a laser using the GaN substrate.
FIG. 9 is a diagram showing the relationship between the impurity concentration in a GaN substrate and the surface roughness of the GaN substrate.
FIG. 10 is a diagram showing a relationship between an impurity concentration in a GaN substrate and a contact specific resistance of an n-type electrode.
FIGS. 11A and 11B are a cross-sectional view of a semiconductor laser fabricated in Example 3 and an impurity concentration profile in the substrate thickness direction.
12A and 12B are a cross-sectional view of a semiconductor laser fabricated in Comparative Example 2 and a diagram showing an impurity concentration profile in the substrate thickness direction.
FIGS. 13A and 13B are a schematic cross-sectional view of a GaN substrate used in Example 4 and a diagram showing an impurity concentration profile in the substrate. FIGS.
14 is a schematic cross-sectional view of another GaN substrate used in Example 4 and a diagram showing an impurity concentration profile in the substrate. FIG.
15 is a schematic cross-sectional view of another GaN substrate used in Example 4, and a diagram showing an impurity concentration profile in the substrate. FIG.
16 is a schematic cross-sectional view of another GaN substrate used in Example 4, and a diagram showing an impurity concentration profile in the substrate. FIG.
17 is a schematic cross-sectional view of another GaN substrate used in Example 4 and a diagram showing an impurity concentration profile in the substrate. FIG.
18 is a schematic cross-sectional view of another GaN substrate used in Example 4, and a diagram showing an impurity concentration profile in the substrate. FIG.
FIG. 19 is a schematic cross-sectional view of a GaN substrate used in Example 5 and a diagram showing an impurity concentration profile in the substrate.
20 is a schematic cross-sectional view of another GaN substrate used in Example 5, and a diagram showing an impurity concentration profile in the substrate. FIG.
FIG. 21 is a schematic sectional view of another GaN substrate used in Example 5 and a diagram showing an impurity concentration profile in the substrate.
22 is a schematic cross-sectional view of another GaN substrate used in Example 5, and a diagram showing an impurity concentration profile in the substrate. FIG.
FIG. 23 is a schematic diagram showing the relationship between the Ga termination surface and N termination surface of GaN grown on the (0001) plane of the seed substrate.
24 is a schematic cross-sectional view of a laser device manufactured in Example 8. FIG.
FIG. 25 is a diagram for explaining an impurity concentration range in a substrate used in the present invention.
26 is a schematic cross-sectional view showing the nitrogen compound semiconductor light-emitting device of Example 9. FIG.
27 is a graph showing the impurity concentration distribution of the nitrogen compound semiconductor substrate used in Example 10. FIG.
28 is a graph showing an impurity concentration distribution of a nitrogen compound semiconductor substrate used in Example 11. FIG.
29 is a graph showing an impurity concentration distribution of a nitrogen compound semiconductor substrate used in Example 12. FIG.
[Explanation of symbols]
101 n-type electrode, 102 GaN substrate, 102A N termination surface, 103 n-type GaN layer, 104 n-type Al _0.1 Ga _0.9 N clad layer, 105 n-type GaN light guide layer, 106 light emitting layer of multiple quantum well, 107 p-type Al _0.2 Ga _0.8 N carrier block layer, 108 p-type GaN light guide layer, 109 p-type Al _0.1 Ga _0.9 N clad layer, 110 p-type GaN contact layer, 111 p-type electrode, 201 n-type electrode, 202 GaN substrate, 202A Ga termination surface, 203 n-type GaN layer, 204 n-type Al _0.1 Ga _0.9 N clad layer, 205 n-type GaN light guide layer, 206 multiple quantum well light emitting layer, 207 p-type Al _0.2 Ga _0.8 N carrier block layer, 208 p-type GaN light guide layer, 209 p-type Al _0.1 Ga _0.9 N clad layer, 210 p-type GaN contact layer, 211 p-type electrode, 301 n-type electrode, 302 GaN substrate, 1001 n-type electrode, 1002 GaN substrate, 1002A N termination surface, 1002a Si highly doped GaN layer, 1002b Si-doped GaN Layer, 1003 n-type GaN layer, 1004 n-type Al _0.1 Ga _0.9 N clad layer, 1005 n-type GaN light guide layer, 1006 multiple quantum well light emitting layer, 1007 p-type Al _0.2 Ga _0.8 N carrier block layer, 1008 p-type GaN light guide layer, 1009 p-type Al _0.1 Ga _0.9 N clad layer, 1010 p-type GaN contact layer, 1011 p-type electrode, 1101 n-type electrode, 1102 GaN substrate, 1102A N termination surface, 1102a Si-doped GaN layer, 1102b Si highly doped GaN layer, 1103 n-type GaN layer, 1104 n-type Al _0.1 Ga _0.9 N clad layer, 1105 n-type GaN light guide layer, 1106 light emitting layer of multiple quantum well, 1107 p-type Al _0.2 Ga _0.8 N carrier block layer, 1108 p-type GaN light guide layer, 1109 p-type Al _0.1 Ga _0.9 N clad layer, 1110 p-type GaN contact layer, 1111 p-type electrode, 1302 GaN substrate whose impurity concentration decreases in the thickness direction, 1302A N termination surface, 1402 GaN substrate, 1402A N termination surface, 1402a GaN layer with constant impurity concentration, 1402b GaN layer with decreasing impurity concentration in the thickness direction, 1402c GaN layer with constant impurity concentration, 1502 GaN substrate, 1502A N termination surface, 1502a GaN layer with decreasing impurity concentration in the thickness direction, 1502b GaN layer with constant impurity concentration, 1502c GaN layer with decreasing impurity concentration in the thickness direction, 1602 GaN substrate, 1602A N termination surface, 1602a GaN layer with constant impurity concentration, 1602b GaN layer with decreasing impurity concentration in the thickness direction, 1602c GaN layer with constant impurity concentration, 1702 GaN substrate 1702A N termination surface, 1802 GaN substrate, 1802A N termination surface, 1902 GaN substrate, 1902A N termination surface, 1902a Si highly doped GaN layer, 1902b Si doped GaN layer, 1902c Si highly doped GaN layer, 1902d Si doped GaN layer, 1902e Si highly doped GaN layer, 2002 GaN substrate, 2002A N termination surface, 2002a, 2002b, 2002c, 2002d, 2002e GaN layer with constant impurity concentration, 2102 GaN substrate, 2102A N termination surface, 2102a, 2102b, 2102c, 2102d, 2102e Impurity GaN layer with constant concentration, 2202 GaN substrate, 2202A N termination surface, 2202a GaN layer with constant impurity concentration, 2202b doped GaN layer with impurity concentration, 2202c GaN layer with constant impurity concentration, 2202d Impurity doped GaN layer, 2202e GaN layer with constant impurity concentration, 2301 seed substrate, 2302 buffer layer, 2303 GaN substrate, 2303a Ga termination surface, 2303b N termination surface, 2304 Ga atom, 2305 N atom, 2401 p-type electrode, 2402 GaN substrate, 2402A main surface, 2403 p-type GaN layer, 2404 p-type Al _0.1 Ga _0.9 N clad layer, 2405 p-type GaN light guide layer, 2406 light emitting layer of multiple quantum well, 2407 n-type Al _0.2 Ga _0.8 N carrier block layer, 2408 n-type GaN light guide layer, 2409 n-type Al _0.1 Ga _0.9 N clad layer, 2410 n-type GaN contact layer, 2410A N termination surface, 2411 n-type electrode, 3001 n-type electrode, 3002 Nitride semiconductor substrate (for example, GaN substrate), 3003 n-type GaN layer, 3004 n-type Al _0.1 Ga _0.9 N-cladding layer, 3005 n-type GaN light guide layer, 3006 multiple quantum well light-emitting layer, 3007 p-type Al _0.2 Ga _0.8 N carrier block layer, 3008 p-type GaN light guide layer, 3009 p-type Al _0.1 Ga _0.9 N cladding layer, 3010 p-type GaN contact layer, 3011 p-type electrode, 3002A N termination surface, 3002a highly doped GaN layer, 3002b low doped GaN layer.

Claims (5)

III-N compound semiconductor substrate,
A plurality of III-N compound semiconductor layers formed on the semiconductor substrate, and an n-type electrode and a p-type electrode for applying a voltage to the plurality of semiconductor layers formed on the semiconductor substrate,
The semiconductor substrate is n-type;
The n-type electrode is formed on a nitrogen termination surface of the semiconductor substrate;
The concentration of the n-type impurity in the semiconductor substrate changes in the thickness direction of the semiconductor substrate,
The semiconductor substrate has a first portion forming the nitrogen termination surface and having a first average n-type impurity concentration, and a second average n-type impurity concentration lower than the first average n-type impurity concentration. The second part,
The first average n-type impurity concentration is 3 × 10 ¹⁸ cm ⁻³ or more,
The III-N-based compound semiconductor device, wherein the second average n-type impurity concentration is 3 × 10 ¹⁸ cm ⁻³ or less, and the plurality of semiconductor layers are formed on the second portion. The first average n-type impurity concentration is in the range of 3 × 10 ¹⁸ cm ⁻³ to 1 × 10 ²¹ cm ⁻³ , and the second average n-type impurity concentration is 1 × 10 ¹⁷ cm ^−. The semiconductor device according to claim 1, which is in a range of ^{3 to} 3 × 10 ¹⁸ cm ⁻³ . 3. The semiconductor device according to claim 2, wherein the first average n-type impurity concentration is within a range of 3 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ . The semiconductor device according to claim 1, wherein the III-N compound semiconductor is a GaN compound semiconductor. The semiconductor device according to claim 1, wherein the semiconductor device is a light emitting element.

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