JPH11186659A - Nitride semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To oscillate a laser beam having a single NFP/FFP at a low threshold in a single mode for a long time. SOLUTION: A p-side clad layer 18 is composed of a super-lattice having a nitride semiconductor layer contg. at least Al with a ridge stripe formed on a part or entire part of the layer 18. At least one end width of the ridge stripe is formed narrow toward a resonance plane to make the horizontal transverse mode single. The total thickness of an n-side clad layer 13 composed of a super-lattice is set for 0.5 μm or more and the mean Al composition of the clad layer 13 in percent is set so that the product of this composition (%) and total thickness (μm) of the clad layer 13 is 4.4 or more, thereby making the vertical transverse mode single.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor (In _a A
_{l b Ga 1-ab N,} 0 ≦ a, 0 ≦ b, relates to a laser device made of a + b ≦ 1).

[0002]

2. Description of the Related Art We have fabricated a nitride semiconductor laser device including an active layer on a nitride semiconductor substrate, and have achieved the world's first continuous oscillation of more than 10,000 hours at room temperature (ICNS). '97 Proceedings, October 27-31, 1997, P444-446,
And Jpn.J.Appl.Phys.Vol.36 (1997) pp.L1568-1571, Pa
rt2, No. 12A, 1 December 1997). FIG. 8 is a schematic sectional view showing the structure of the laser device. The basic structure is such that S formed in stripes on a sapphire substrate
A plurality of nitride semiconductor layers forming a laser element structure are stacked on a nitride semiconductor substrate made of n-GaN selectively grown via an iO ₂ film. (For details, see Jpn.J.Appl.Phy
s.Vol.36)

The basic structure of a laser device is In _0.02 Ga
An active layer in which a barrier layer made of _0.98 N and a well layer made of In _0.15 Ga _0.85 N are stacked on each other is formed of n-Al _0.14 Ga _0.86
An n-side cladding layer having a superlattice structure composed of N / GaN;
It has a double hetero structure sandwiched between a p-side cladding layer having a superlattice structure composed of p-Al _0.14 Ga _0.86 N / GaN. Each of the single nitride semiconductor layers constituting the superlattice has a thickness of 25 Å. Further, a ridge having the same stripe width is formed above a part of the p-type cladding layer. Light emission from the active layer is concentrated in the waveguide region below the ridge stripe, resonates between the resonance surfaces, and is emitted as a laser.

[0004]

However, in the conventional laser device, the laser light tends to be multi-mode. In the horizontal and transverse modes, a single mode is achieved by narrowing the ridge stripe. However, if the stripe width is reduced to obtain a single mode, it tends to be difficult to form an ohmic electrode formed on the ridge stripe. . In addition, since the electrode area is reduced, the current is concentrated on a minute portion, so that the threshold value of the laser element increases, and the reliability of the element itself decreases due to heat generation.

On the other hand, in the vertical and transverse modes, the confinement of light by both cladding layers still tends to be insufficient. For example, light leaked from the n-side cladding layer is reflected by a sapphire substrate having a small refractive index and guided in a GaN layer having a large refractive index between the substrate and the n-side cladding layer. The light guided in the GaN layer overlaps the laser light emitted from the end face of the active layer and disturbs the shape of the far field pattern (FFP). For example, a plurality of emitted laser light spots appear, Mode is observed. A multi-mode laser element is very difficult to use as a pickup light source.

Accordingly, it is an object of the present invention to provide a single mode NFP or FFP for using a nitride semiconductor laser device as various light sources and to oscillate laser light for a long time at a low threshold. .

[0007]

A nitride semiconductor laser device according to the present invention comprises an n-side cladding layer, an active layer,
Side in order, and a layer above the active layer,
In a nitride semiconductor laser device having a ridge stripe substantially perpendicular to an opposing resonance surface, the p-side cladding layer is composed of a superlattice having at least a nitride semiconductor layer containing Al, and a part of the p-side cladding layer. Or the entire ridge stripe is formed, and at least one of the stripe widths of the ridge is formed so as to become narrower as approaching the resonance surface.

Further, the ridge stripe is characterized in that the stripe width on the output side is narrower than the stripe width on the total reflection side. The laser output side and total reflection side can be appropriately determined, for example, by adjusting the reflectance of a reflection film formed on the resonance surface.

In the laser device according to the present invention, the n-side cladding layer is made of a superlattice having at least a nitride semiconductor layer containing Al, and the entire thickness of the n-side cladding layer is 0.5 μm or more. In addition, when the Al average composition contained in the n-side cladding layer is expressed in percentage (%), the product of the thickness (μm) of the entire n-side cladding layer and the Al average composition (%) is 4.4 or more. It is characterized by being constituted so that it becomes.

Further, when the total thickness of the p-side cladding layer is 2.0 μm or less and the average Al composition contained in the p-side cladding layer is expressed by percentage (%), Is characterized in that the product of the thickness (μm) and the average Al composition (%) is 4.4 or more.

Further, in the laser device of the present invention,
The thickness of the nitride semiconductor layer including the active layer between the n-side and p-side cladding layers is in the range of not less than 200 Å and not more than 1.0 μm.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a laser device according to the present invention, a cladding layer is a light confinement layer containing a nitride semiconductor having a lower refractive index than that of a well layer of an active layer. The superlattice refers to a multilayer structure in which a single layer has a thickness of 100 angstroms or less and nitride semiconductor layers having different compositions are stacked, and preferably has a thickness of 70 angstroms or less, more preferably 40 angstroms or less. The semiconductor layers are stacked. As a specific configuration, for example, Al _X G
a _1-X N (0 <X <1) layer and another nitride semiconductor layer having a composition different from that of the Al _X Ga _1-X N layer are formed as a superlattice, for example, Al _X Ga _1-X N / GaN, Al _X Ga _1-X N /
Al _Y Ga _1-Y N (0 <Y <1, Y <X), Al _X Ga _{1- X} N
_{/ In Z Ga 1-Z N} (0 <Z <1) 3 -element mixed crystal and ternary mixed crystal such as, or in combination with ternary mixed crystal and the binary mixed crystal as a super-lattice. Among them, most preferably, Al
_The superlattice is made of XGa ₁ -XN and GaN. this is,
The same applies to the case where the n-side cladding layer is a superlattice. It goes without saying that the cladding layer and the active layer need not be formed in contact with each other.

FIG. 1 is a schematic perspective view showing the shape of the laser device of the present invention, and also shows a laminated structure. FIG. 2 is a plan view of the laser device of FIG. 1 as viewed from the ridge side. In this laser device, a ridge stripe is formed on a part of the p-side cladding layer 18 made of a superlattice, and one of the stripe widths of the ridge is formed to be narrower as approaching the resonance surface, and the other stripe width is formed. Are formed so as to become wider as approaching the resonance surface.

As described above, preferably, by narrowing the stripe width on the output side of the ridge and widening the total reflection side on the other side, the laser beam below the ridge has a horizontal mode in a single mode where the stripe width is narrow. Becomes On the other hand, where the stripe width is wide, there is a possibility of multimode at the bottom of the ridge, but since it is already single at the narrow part, while the guided light resonates between the resonance surfaces, Since the multimode is attenuated at a narrow portion, the laser light emitted from the resonance surface corresponding to the wide portion of the stripe also becomes a single mode. Also,
The part where the stripe width of the ridge gradually narrows,
Because there is a part that is gradually widened, the surface area is almost the same as that with stripe width at equal intervals,
Alternatively, since the current can be substantially widened, current does not concentrate in a narrow region and flows evenly in the ridge, so that heat generation of the element itself is reduced and reliability is improved.

FIG. 4 is a plan view showing the shape of the ridge.
Unlike FIG. 2, the n-electrode is omitted. To explain with reference to this figure, when forming a stripe ridge, the stripe width a on the output side is 0.5 μm to 5 μm, more preferably 1 μm to 5 μm.
It is desirable to adjust to a range of μm to 2 μm. 0.5
When the thickness is smaller than μm, the ridge width of the contact layer laminated on the cladding layer is similarly reduced, so that it tends to be difficult to form an ohmic p-electrode. On the other hand, the stripe width b on the total reflection side is 2 μm to 20 μm.
μm, and more preferably, it is desirable to adjust to a range of 4 μm to 6 μm. If it is smaller than 2 μm, the other stripe width “a” must be smaller than 2 μm. Therefore, the entire ridge width becomes too narrow, and the current tends to concentrate on the ridge, so that the element tends to generate heat. On the other hand, when the width is larger than 20 μm, the loss of light at the lower part of the ridge tends to be large and the output tends to decrease.

It is most preferable that the stripe shape of the ridge has no "constriction" in the middle as shown in FIG. 4 and is narrowed to one side at a fixed angle. In the present invention, it is desirable that the angle be as small as possible. For example, the angle θ with respect to a direction parallel to the laser resonance direction is adjusted within 10 °, more preferably within 8 °, and most preferably within 5 °. When the angle becomes steep, light leaks to the outside from the steep portion and it is difficult for the light to concentrate at the lower part of the ridge, so the efficiency as a laser deteriorates, the output decreases, and the threshold tends to increase. It is in. Therefore, in the present invention, it is desirable to form a ridge stripe that gradually narrows as it approaches the end face at as gentle an angle as possible, with the narrow side being the output side and the wide side being the total reflection side. As a preferable ridge stripe, the output side a is 1 to
It is most preferable to form a ridge stripe having an inclination angle of 3 ° with 3 μm and a total reflection side of 3 to 8 μm.

FIGS. 5 to 7 are plan views showing other shapes of the ridge stripe according to the present invention. In the present invention, as shown in FIGS. 5 and 6, both ridge stripes may be formed so as to have a smaller width as approaching the resonance surface. Further, as shown in FIG. 7, the shape may be such that one becomes narrower and the other becomes wider as approaching the resonance surface in the middle of the stripe. However, as shown in FIGS. 5 to 7, when the width is sharply narrowed from a wide stripe width, the angle θ increases, so that light easily leaks from the narrow portion, and the laser output tends to decrease. Therefore, even when forming the ridge stripe as shown in FIGS. 5 to 7, it is desirable to adjust the inclination angle to within 10 °.

Further, in the present invention, the n-side cladding layer is made of a superlattice having a nitride semiconductor layer containing at least Al, and the entire thickness of the n-side cladding layer is 0.5 μm.
m or more and when the average Al composition contained in the n-side cladding layer is expressed as a percentage (%), the product of the thickness (μm) of the entire n-side cladding layer and the average Al composition (%) is 4 .4 or more, the laser beam in the vertical / lateral mode can be controlled, and the mode is likely to be single mode. n
If the thickness of the side cladding layer is smaller than 0.5 μm and the product of the total thickness (μm) of the entire n side cladding layer and the average Al composition (%) is smaller than 4.4, the n side cladding layer The light confinement is insufficient, and the light is guided by the n-side contact layer, FFP is disturbed, and the threshold value tends to increase. A preferable value of the product is 5.0 or more, more preferably 5.4 or more. The best mode is adjusted to 7 or more.

For example, the total thickness of the n-side cladding layer is 0.8 μm or more, and the average Al composition contained in the n-side cladding layer is 5.5% or more. The product in this case is 4.4 or more. Preferably, the total thickness of the n-side cladding layer is 1.0 μm or more, and the average Al composition contained in the n-side cladding layer is 5.0% or more. The product in this case is greater than or equal to 5.0. More preferably, the total thickness of the n-side cladding layer is 1.2 μm or more, and the average Al composition contained in the n-side cladding layer is 4.5% or more. The product in this case is 5.4 or more. This is because the relationship between the thickness of the n-side cladding layer and the Al
It specifically shows the relationship of the average composition.

Also, for the p-side cladding layer, when the total thickness of the p-side cladding layer is 2.0 μm or less and the average Al composition contained in the p-side cladding layer is expressed in percentage (%), It may be configured such that the product of the thickness (μm) of the entire side cladding layer and the average Al composition (%) is 4.4 or more. With this configuration, the laser beam in the vertical / lateral mode can be controlled, and the mode is likely to be single mode. Note that p
More preferably, the n-side cladding layer has the above-mentioned structure than the side cladding layer. This is because the p-side cladding layer is formed as a ridge stripe having the shape as in the present application and an electrode is provided thereon, and light is absorbed by the electrode. Because you can.

However, when the p-side cladding layer is configured as described above, it is desirable that the thickness of the p-side cladding layer be smaller than that of the n-side cladding layer. The reason is that when the Al average composition of the p-side cladding layer is increased or the film thickness is increased, the resistance value of the AlGaN layer tends to increase, and when the resistance value of AlGaN increases, the driving voltage tends to increase. Because. As a preferable film thickness,
The thickness is 1.5 μm or less, more preferably 1 μm or less.
Although the lower limit is not particularly limited, it is desirable that the film has a thickness of 50 Å or more in order to function as a cladding layer.
% Is desirable.

[0022] Generally, in accordance with the Al _X Ga _1-X N is increased the Al mixed crystal ratio, the band gap energy increases, it is known that even smaller refractive index. Ideally, Al _x Ga having a large Al mixed crystal ratio X, for example, 0.5 or more
It would be industrially convenient if the _1-X N layer could be grown as a single layer with a thickness of, for example, several μm.
l _x Ga ₁ -xN is a thick film and is difficult to grow. A single layer
When growing Al _x Ga ₁ -xN having a mixed crystal ratio of 0.5 or more, cracks may be formed in the crystal at, for example, 0.1 μm or more. However, as in the present invention, Al _x Ga ₁ -xN
Is a thin film constituting a superlattice, a single film thickness A
Since the thickness is less than or equal to the critical limit film thickness of l _x Ga ₁ -xN, cracks are unlikely to occur. Therefore, if the cladding layer is a superlattice, A
Even a layer having a high mixed crystal ratio can be grown as a thick film. By combining them, it is possible to prevent light from leaking from the n-side cladding layer to the substrate side.

In the present invention, the Al average composition in the superlattice is determined by the following calculation method. For example, 25 Å of Al _0.5 Ga _0.5 N and 25 Å
200 pairs of Angstrom GaN (1.0 μm)
In the case of a stacked superlattice, one pair is 50 angstroms, and the layer containing Al has an Al mixed crystal ratio of 0.5.
0.5 (25/50) = 0.25, and the average Al composition in the superlattice is 25%. On the other hand, when the film thickness is different, Al _0.5 Ga _0.5 N is set to 40 Å and Ga
When N is stacked at 20 angstroms, a weighted average of the film thickness is obtained, and 0.5 (40/60) = 0.33, and the Al average composition is 33.3%. That is, a value obtained by multiplying the ratio of the Al mixed crystal of the nitride semiconductor layer containing Al to the ratio of the nitride semiconductor layer to the film thickness of one pair of superlattices is defined as the Al average composition of the superlattice in the present invention. The same applies to the case where both Al are contained. For example, in the case of Al _0.1 Ga _0.9 N 20 Å and Al _0.2 Ga _0.8 N30 Å, 0.1 (20/50) +0.2 (30/5)
0) = 0.16, that is, 16% is the Al average composition. The above examples are AlGaN / GaN, AlGaN / AlG
Although aN has been described, the same calculation method is applied to AlGaN / InGaN. Therefore, n
When growing the side cladding layer, a growth method can be designed based on the above calculation method. The Al average composition of the n-side cladding layer can also be detected by using an analyzer such as SIMS (secondary ion mass spectrometer) and Auger.

[0024]

[Embodiment 1] Embodiment 1 will be described with reference to FIGS. FIG. 3 is a schematic cross-sectional view showing a structure after a p-electrode is formed on the laser device of FIG. 1, and the portions denoted by the same reference numerals in FIGS.

(Underlayer 2) A heterogeneous substrate 1 made of sapphire having a 2-inch φ and C-plane as a main surface is set in a MOVPE reactor, the temperature is set to 500 ° C., and trimethylgallium (TMG), ammonia (NH ₃ ) Using GaN
A buffer layer (not shown) is grown to a thickness of 200 Å. After growing the buffer layer, set the temperature to 1
050 ° C., and the underlayer 2 also made of GaN was
It is grown to a thickness of m. The underlayer 2 has a protective film partially formed on its surface, and then functions as an underlayer for selectively growing a nitride semiconductor substrate. The underlayer 2 is made of Al _x Ga ₁ -xN (0 ≦ X ≦ 0.5) having an Al mixed crystal ratio X value of 0.5 or less.
It is desirable to grow. If it exceeds 0.5, the crystal itself tends to be cracked rather than a crystal defect, and the crystal growth itself tends to be difficult.
Also, the film is grown with a thickness larger than that of the buffer layer.
It is desirable to adjust the film thickness to 0 μm or less. The substrate is sapphire, SiC, ZnO, spinel, GaAs
For example, a substrate made of a material different from a nitride semiconductor, which is known for growing a nitride semiconductor, can be used.

(Protective Film 3) After the growth of the underlayer 2, the wafer is taken out of the reaction vessel, a stripe-shaped photomask is formed on the surface of the underlayer 2, and a stripe width of 10 μm and a stripe interval (window portion) are formed by a CVD apparatus. ) 2 μm S
A protective film 3 made of iO ₂ is formed with a thickness of 1 μm. The shape of the protective film may be any shape such as a stripe shape, a dot shape, a grid shape, and the like. Easy to grow. Examples of the material of the protective film include oxides and nitrides such as silicon oxide (SiO _x ), silicon nitride (Si _x N _y ), titanium oxide (TiO _x ), and zirconium oxide (ZrO _x ), and multilayer films thereof. And 1200
A metal or the like having a melting point of not less than ° C. can be used. These protective film materials have a nitride semiconductor growth temperature of 600 ° C.
It withstands temperatures of up to 1100 ° C., and has the property that nitride semiconductors do not grow or hardly grow on the surface.

(Nitride semiconductor substrate 4) After forming the protective film 3,
The wafer is set again in the MOVPE reaction vessel, the temperature is set to 1050 ° C., and a nitride semiconductor substrate 4 made of undoped GaN is grown to a thickness of 20 μm using TMG and ammonia. On the surface of the nitride semiconductor substrate 4 after the growth, crystal defects appeared parallel to the stripe-shaped protective film in the center of the stripe of the protective film and in the center of the stripe of the window. By preventing the ridge stripe from being related to this crystal defect at the time of formation, the crystal defect does not dislocation in the active layer,
The reliability of the device is improved. The nitride semiconductor substrate 4 can be grown using the halide vapor phase epitaxy (HVPE), but can also be grown using the MOVPE method. The nitride semiconductor substrate has a G content not containing In and Al.
It is most preferable to grow aN, and as a gas at the time of growth, an organic gallium compound such as triethyl gallium (TEG) is used in addition to TMG, and ammonia or hydrazine is most preferably used as a nitrogen source. Also,
The GaN substrate may be doped with an n-type impurity such as Si or Ge to adjust the carrier concentration to an appropriate range. In particular, when removing the heterogeneous substrate 1, the underlayer 2, and the protective film 3, the nitride semiconductor substrate serves as a contact layer. Therefore, it is desirable to dope the nitride semiconductor substrate 4 with an n-type impurity.

(N-side buffer layer 11 = n-side contact layer) Next, using ammonia and TMG, and silane gas as an impurity gas, Si is deposited on the second nitride semiconductor
An n-side buffer layer 11 of GaN doped with × 10 ¹⁸ / cm ³ is grown to a thickness of 5 μm. When a light emitting device having a structure as shown in FIG.
Acts as a contact layer for forming electrodes. In the case where an electrode is provided on the nitride semiconductor substrate 4 by removing the heterogeneous substrate 1 to the protective film 3, it may be omitted. The n-side buffer layer 11 is a buffer layer grown at a high temperature, for example, on a substrate made of a material different from a nitride semiconductor such as sapphire, SiC, and spinel.
GaN, AlN, etc., at a low temperature
It is distinguished from a buffer layer directly grown with a thickness of less than m.

(Crack prevention layer 12) Next, TMG, T
Using MI (trimethylindium) and ammonia at a temperature of 800 ° C., a crack prevention layer 12 of In _0.06 Ga _0.94 N is grown to a thickness of 0.15 μm.

(N-side cladding layer 13 = superlattice layer) Subsequently, n-type A doped with Si at 1 × 10 ¹⁹ / cm ³ using TMA, TMG, ammonia and silane gas at 1050 ° C.
A first layer of l _0.16 Ga _0.84 N is grown to a thickness of 25 angstroms, then silane gas and TMA are stopped, and a second layer of undoped GaN is grown to a thickness of 25 angstroms. Then, a superlattice layer is formed in the order of first layer + second layer + first layer + second layer +..., And an n-side cladding layer 13 composed of a superlattice having a total film thickness of 1.2 μm is grown. Since the n-side cladding layer made of this superlattice has an average Al composition of 8.0%, the product of the thickness and the thickness is 9.6. Note that when a superlattice in which nitride semiconductors having different band gap energies are stacked on the n-side cladding layer is manufactured, one of the layers is heavily doped, and the threshold value tends to decrease when so-called modulation doping is performed. It is in.

(N-side light guide layer 14) Subsequently, the silane gas is stopped and the n-side light guide layer 14 made of undoped GaN is grown at 1050 ° C. to a thickness of 0.1 μm. This n-side light guide layer acts as a light guide layer of the active layer,
It is desirable to grow GaN or InGaN, usually 100 Å to 5 μm, more preferably 2 Å.
It is desirable to grow with a film thickness of 00 Å to 1 μm.

(Active Layer 15) Next, the active layer 14 is grown using TMG, TMI and ammonia. The temperature of the active layer is maintained at 800 ° C., and a well layer made of undoped In _0.2 Ga _0.8 N is grown to a thickness of 40 Å. Next, a barrier layer made of undoped In _0.01 Ga _0.95 N is added at the same temperature only by changing the molar ratio of TMI.
It is grown to a thickness of 00 Å. A well layer and a barrier layer are sequentially stacked, and finally terminated with a barrier layer.
An active layer of 40 Å multiple quantum well structure (MQW) is grown. The active layer may be undoped as in this embodiment, or may be doped with an n-type impurity and / or a p-type impurity. The impurity may be doped into both the well layer and the barrier layer, or may be doped into either one.

(P-side cap layer 16)
Raise to 50 ° C, TMG, TMA, ammonia, Cp2M
g (cyclopentadienyl magnesium), p-type Al _0.3 Ga doped with Mg at 1 × 10 ²⁰ / cm ³ and having a larger band gap energy than the p-side light guide layer 17
_A p-side cap layer 16 of _0.7 N is grown to a thickness of 300 Å. When the p-type cap layer 16 is formed with a thickness of 0.1 μm or less, the output of the device tends to be improved. Although the lower limit of the film thickness is not particularly limited, it is desirable to form the film with a film thickness of 10 Å or more.

(P-side light guide layer 17) Subsequently, Cp2M
g, TMA is stopped, and at 1050 ° C., a p-side optical guide layer 17 made of undoped GaN having a band gap energy smaller than that of the p-side cap layer 16 is grown to a thickness of 0.1 μm. This layer acts as a light guide layer of the active layer and, like the n-type light guide layer 14, GaN, InGaN
It is desirable to grow with.

(P-side cladding layer 18)
P-type Al _0.16 G doped with Mg at 1 × 10 ²⁰ / cm ³
a third layer consisting of a _{0.8 4} N is grown to the thickness of 25 Å, followed by stopping the TMA alone, undoped G
A fourth layer of aN is grown to a thickness of 25 Å, and a p-side cladding layer 18 of a superlattice layer having a total thickness of 0.6 μm is grown. This p-side cladding layer is also made of Al
Is 8%, so the product of the film thickness and the film thickness is 4.8. Note that when the p-side cladding layer is also manufactured using a superlattice in which at least one of the layers includes a nitride semiconductor layer containing Al and has different band gap energies from each other, impurities are heavily doped in one of the layers. do it,
When so-called modulation doping is performed, the threshold value tends to decrease.

Here, the thickness of the core portion (waveguide portion) sandwiched between the cladding layers will be described. The core part is n
Side light guide layer 14, active layer 15, p-side cap layer 16,
And a region where the p-side light guide layer 17 is combined, that is, a nitride semiconductor layer including an active layer between the n-side clad layer and the p-side clad layer, and is a region where light emission of the active layer is guided. . In the case of the nitride semiconductor laser device, the reason why the FFP does not become a single beam is that, as described above, light emitted from the cladding layer is guided in the n-side contact layer and becomes a multimode. is there. In addition, there is a case where a multi-mode is caused by resonance in the core. In the present invention, first, the thickness of the n-side cladding layer is increased to increase the Al average composition, thereby providing a refractive index difference and confining the light in the core by the cladding layer. However, when the multi-mode is formed in the core, the FFP is disturbed. Therefore, in relation to the n-side cladding layer of the present invention, it is desirable to also adjust the thickness of the core portion so as not to be multimode in the core. The preferred thickness for preventing multimode from occurring in the core portion is 200 Å or more, 1.0 μm or less,
More preferably, 500 Å to 0.8 μm
m, most preferably in the range of 0.1 μm to 0.5 μm. If the thickness is less than 200 angstroms, light leaks from the core and the threshold value tends to increase. On the other hand, if the thickness is more than 1.0 μm, multi-mode tends to be easily caused.

(P-side contact layer 19) Finally, 105
At 0 ° C., 2 × 10 ²⁰ Mg is applied on the p-side cladding layer 18.
A p-side contact layer 18 made of p-type GaN doped with / cm ³ is grown to a thickness of 150 Å. p
The side contact layer 19 is a p-type In _x Al _Y Ga _{1 -XYN}
(0 ≦ X, 0 ≦ Y, X + Y ≦ 1), preferably Mg-doped GaN, the p-electrode 21
And the most preferable ohmic contact is obtained.

The wafer on which the nitride semiconductor has been grown as described above is placed in a reaction vessel in a nitrogen atmosphere at 700.degree.
Annealing is performed at a temperature of ° C. to further reduce the resistance of the layer doped with the p-type impurity.

After the annealing, the wafer is taken out of the reaction vessel, and the uppermost p-side contact layer 18 and a part of the p-side cladding layer 17 are etched by the RIE apparatus to obtain a structure as shown in FIGS. A ridge stripe having a shape is formed. In this ridge stripe, the stripe width on one resonance surface side is set to 2.0 μm, the stripe width on the other resonance surface side is set to 4.0 μm, and the resonator length is set to 500 μm. The angle θ with respect to the laser resonance direction is set to 3 ° or less. In this embodiment, a part of the p-side cladding layer is formed as a ridge stripe, but the etching depth may be increased and the entire p-side cladding layer may be formed as a ridge stripe.

In forming the ridge stripe, the ridge stripe is formed at a position where no crystal defect appears on the surface of the nitride semiconductor substrate. Crystal defects tend to appear at the center of the stripe-shaped protective film 3 and at the center of the striped window. Therefore, by forming the ridge stripe avoiding the central portion, the crystal defects tend not to extend to the active layer, so that the device can have a long life and the reliability is improved.

Next, a mask is formed on the ridge surface, and RIE is performed.
To expose the surface of the n-side buffer layer 11. The exposed n-side buffer layer 11 also functions as a contact layer for forming the n-electrode 23.

Next, on the outermost surface of the ridge of the p-side contact layer 19, a p-electrode 20 made of Ni and Au is formed in a stripe shape, while the n-electrode 22 made of Ti and Al is exposed previously. Then, an insulating film 23 made of SiO ₂ is formed on the surface of the nitride semiconductor layer exposed between the p-electrode 20 and the n-electrode 22 as shown in FIG. A p-pad electrode 21 electrically connected to the p-electrode 20 via the film 23 is formed.
The p pad electrode absorbs light leaking to the p layer side.

As described above, after the sapphire substrate of the wafer on which the n-electrode and the p-electrode are formed is polished to 70 μm, the wafer is cleaved into a bar from the substrate side in a direction perpendicular to the stripe-shaped electrodes. A resonator is formed on the cleavage plane. Forming a dielectric multilayer film composed of SiO ₂ and TiO ₂ on the resonator surface,
Finally, the bar is cut in a direction parallel to the p-electrode to form a laser device.

This laser element is set on a heat sink,
When each electrode was wire-bonded and laser oscillation was attempted at room temperature, continuous oscillation was exhibited at room temperature, and a single laser beam had a single FFP and an elliptical shape with good shape. . Also, as for the characteristics of the laser device, the threshold value was reduced by 15% or more and the life was improved by 60% or more as compared with the one published by Jpn. J. Appl. Phys. Vol. 36 (1997).

Example 2 In Example 1, when growing the n-side cladding layer 13, the Si-doped n-type Al _0.20
Ga _0.80 N25 Å and undoped GaN
A laser element was fabricated in the same manner as described above except that a layer having a thickness of 25 Å was laminated and an n-side cladding layer 13 composed of a superlattice having a total film thickness of 1.0 μm was grown. The n-side cladding layer is made of Al
Since the average composition is 10.0%, the product with the film thickness is 1
0.0. This laser element also had almost the same characteristics as those of the first embodiment.

Example 3 In Example 1, when growing the n-side cladding layer 13, Si-doped n-type Al _0.20
Ga _0.80 N25 Å and undoped GaN
A laser element was manufactured in the same manner as above except that a layer having a thickness of 25 Å was laminated and an n-side cladding layer 13 composed of a superlattice having a total film thickness of 0.7 μm was grown. Since the n-side cladding layer has an average Al composition of 1.0%, the product of the n-side cladding layer and the film thickness is 7.0. This laser element also had almost the same characteristics as those of the first embodiment.

Example 4 In Example 1, when growing the n-side cladding layer 13, Si-doped n-type Al _0.12
Ga _0.88 N25 Å and undoped GaN
A laser element was fabricated in the same manner as described above, except that a layer having a thickness of 25 Å was laminated and an n-side cladding layer 13 composed of a superlattice having a total film thickness of 0.8 μm was grown. Since the Al average composition of the n-side cladding layer is 6.0%, the product of the n-side cladding layer and the film thickness is 4.8. This laser element also has an FFP equivalent to that of the first embodiment. The threshold value is reduced by 8% or more and the life is 30% or more as compared with the one disclosed in Jpn.J.Appl.Phys.Vol.36 (1997). Improved.

Fifth Embodiment In the first embodiment, when growing the n-side cladding layer 18, the Si-doped n-type Al _0.07
Ga _0.93 N layer 25 Å, undoped Ga
A laser element was fabricated in the same manner except that an N layer was grown to a thickness of 25 Å with a total thickness of 1.4 μm. Since the average composition of the n-side cladding layer is 3.5%, the product of the n-side cladding layer and the film thickness is 4.9. This laser device exhibited almost the same characteristics as those of Example 4.

Sixth Embodiment In the first embodiment, when forming a stripe-shaped ridge, the ridge is formed as shown in FIG. However, in FIG. 5, the stripe width on both output sides is 2 μm, and the stripe width on the center is 4 μm.
μm, and adjust the inclination angle to within 5 °. This laser element also exhibited almost the same characteristics as those of the first embodiment.

[0050]

As described above, according to the present invention, a single mode can be obtained in both the horizontal and horizontal modes and the vertical and horizontal modes. In addition, the pot shape for extending the laser beam also becomes a single ellipse, and a constant FFP can be obtained. Since nitride semiconductors use a material called sapphire, which has a lower refractive index than nitride semiconductors, it seems that conventional problems have been unavoidable, but the present invention is not limited to sapphire, and it is more refractory than nitride semiconductors. Even if a laser element is manufactured on any substrate having a low efficiency, a single mode laser beam with a clean shape can be obtained, and therefore, its use value as a light source for writing and reading is very large.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the structure of a laser device according to one embodiment of the present invention.

FIG. 2 is a plan view of the laser device of FIG. 1 as viewed from above a ridge.

FIG. 3 is a schematic cross-sectional view showing a structure after a p-electrode is formed on the laser device of FIG.

FIG. 4 is a plan view showing the shape of a ridge stripe.

FIG. 5 is a plan view showing one shape of a ridge stripe of the laser device according to the present invention.

FIG. 6 is a plan view showing one shape of a ridge stripe of the laser device according to the present invention.

FIG. 7 is a plan view showing one shape of a ridge stripe of the laser device according to the present invention.

FIG. 8 is a schematic sectional view showing the structure of a conventional laser device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Different substrate 2 ... GaN base layer 3 ... Protective film 4 ... Nitride semiconductor substrate 11 ... n-side buffer layer 12 ... crack prevention layer 13 ... n-side cladding layer 14 n-side light guide layer 15 active layer 16 p-side cap layer 17 p-side light guide layer 18 p-side cladding layer 19 p-side contact layer 20 ..P electrode 21 ... p pad electrode 22 ... n electrode 23 ... insulating film

Claims (5)

[Claims] 1. An n-side cladding layer on a substrate, an active layer,
and a p-side cladding layer in order, and in a layer above the active layer, a nitride semiconductor laser device having a ridge stripe substantially perpendicular to an opposing resonance surface, wherein the p-side cladding layer contains at least Al. A ridge stripe is formed on a part or all of the p-side cladding layer, and at least one of the stripe widths of the ridge becomes narrower as approaching the resonance surface. A nitride semiconductor laser device characterized by being formed as follows. 2. The nitride semiconductor laser device according to claim 1, wherein the ridge stripe has a stripe width on a laser output side smaller than a stripe width on a total reflection side. 3. An n-side cladding layer comprising at least Al
Consisting of a superlattice having a nitride semiconductor layer containing
The thickness of the entire side cladding layer is 0.5 μm or more, and the average Al composition contained in the n-side cladding layer is expressed as a percentage (%).
When expressed by, the thickness (μm) of the entire n-side cladding layer and A
3. The nitride semiconductor laser device according to claim 1, wherein a product of the average composition (%) and the average composition (%) is 4.4 or more. 4. 4. The thickness of the entire p-side cladding layer is 2.0
μm or less and contained in the p-side cladding layer.
When the 1-average composition is expressed in percentage (%), the product of the thickness (μm) of the entire p-side cladding layer and the Al average composition (%) is 4.4 or more. The nitride semiconductor laser device according to any one of claims 1 to 3, wherein: 5. The nitride semiconductor layer including an active layer between the n-side and p-side cladding layers has a thickness in a range from 200 Å to 1.0 μm. Item 5. The nitride semiconductor laser device according to any one of items 1 to 4.