JP3925066B2 - Nitride semiconductor laser device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser element made of a nitride semiconductor (In _X Al _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1), and in particular controls self-oscillation, and controls vertical FFP and self-oscillation. The present invention relates to a laser element that optimizes both the excitation oscillation power.
[0002]
[Prior art]
Semiconductor light-emitting elements are expected to be applied in various fields, and research and development have been actively promoted in recent years. In particular, various research and development have been actively conducted on nitride semiconductor laser diodes (LDs), and practical LDs have also been developed.
[0003]
The nitride semiconductor laser device has a layer structure in which an active layer is sandwiched between optical confinement layers (cladding layers). Light spontaneously emitted from the active layer is totally reflected between the p-side and n-side clad layers and is amplified in the waveguide layer (light guide layer) having the active layer, and the amplified light is activated as stimulated emission light. It emits from the layer end face (resonant face).
[0004]
The present inventor has produced a nitride semiconductor laser device including an active layer on a nitride semiconductor substrate, and has achieved the world's first continuous oscillation of 10,000 hours or more at room temperature (ICNS'97 Proceedings, October 27-31, 1997, P444-446, and Jpn. J. Appl. Phys. Vol. 36 (1997) pp. L1568-1571, Part 2, No. 12A, 1 December 1997).
[0005]
In order to realize a semiconductor laser with good characteristics, it is necessary to efficiently inject current into the active layer and confine light in the active layer. For example, as an InGaN-based laser diode structure, a separate confinement type laser using a multi-quantum well structure InGaN light-emitting layer with a GaN light guide layer and an AlGaN / GaN superlattice structure as a cladding layer has been announced (Applied Physics) 68 (7) (1999) 795). In this example, periodic ripples are observed in the FFP in the vertical direction. This is because the light confinement by the AlGaN / GaN cladding layer is insufficient, so that a part of the laser beam leaks to the GaN contact layer. Are listed. As a countermeasure, the necessity of increasing the light confinement by increasing the Al composition ratio of the cladding layer or increasing the thickness is cited. In general, a semiconductor laser obtains a carrier confinement effect by a double heterostructure and efficiently obtains an inversion distribution, and confines emitted light in a guide layer to cause stimulated emission to obtain light confinement. In order to realize this, the refractive index of light of the active layer material is designed to be higher than the refractive index of the cladding layer material.
[0006]
In addition, the semiconductor laser needs to reduce the threshold current density. For this purpose, it is a common practice to enhance light confinement. For example, Japanese Patent Application Laid-Open No. 11-238945 discloses a method of obtaining a laser element in which the laser light of a nitride semiconductor laser element is made into a single mode and the oscillation threshold value is lowered by improving the light confinement effect of the cladding layer. be written. In this method, the n-side cladding layer is composed of a superlattice having a nitride semiconductor layer containing Al, the entire thickness of the n-side cladding layer is 0.5 μm or more, and Al contained in the n-side cladding layer When the average composition is expressed as a percentage (%), the product of the thickness (μm) of the entire n-side cladding layer and the Al average composition (%) is 4.4 or more. In addition, by adjusting the thickness of the nitride semiconductor layer including the active layer between the n-side and p-side cladding layers to a range of 200 angstroms or more and 1.0 μm or less, light is confined in the core portion. The vertical and transverse modes of the laser beam are converted to single mode.
[0007]
[Problems to be solved by the invention]
However, a structure that enhances the light confinement tends to cause self-excited oscillation because the light density of the active layer increases. Self-excited oscillation refers to a state in which the output waveform that should be constant starts to oscillate when the current value applied to the laser is increased. In order to prevent this, there is a method of reducing the light density. However, light confinement is required to realize laser oscillation. Thus, the confinement of light and the prevention of self-excited oscillation are in a trade-off relationship, and there is a problem that self-excited oscillation occurs if the confinement of light is strong.
[0008]
The present invention is intended to solve such problems. An important object of the present invention is to control the generation of self-oscillation and to reduce the vertical FFP by intentionally weakening the confinement of light with a concept opposite to the conventional one and leaking light. An object of the present invention is to provide a nitride semiconductor laser device that can be used.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the nitride semiconductor laser device of the present invention has the following configuration.
[0010]
Nitride semiconductor laser device described in this onset Ming includes p and n-side optical guide layer between the n-side and p-side cladding layer and the average composition of the 0.02 to 0.04 Al, the InGaN An active layer is formed, the p and n side light guide layers have a nitride semiconductor layer containing at least Al, and the average composition of Al contained in the p and n side light guide layers is a cladding layer The thickness of the core portion sandwiched between the cladding layers is 200 angstroms or more and 1.0 um or less, and the ridge of the laser device is set to a value smaller than the average Al composition. The stripe is formed up to the region of the p-side light guide layer.
[0011]
As described above, the present invention can prevent self-oscillation without increasing the threshold current density by weakening the light confinement by mixing Al in the light guide layer and increasing the Al ratio.
[0012]
Weakening the confinement of light by reducing the ratio of Al contained in the clad layer can be a threshold current density to prevent self-oscillation without significantly.
[0013]
The total thickness of the or n-side cladding layer can be prevented ripple more leakage light impact on the 1μm~2μm and child.
[0014]
Superlattice constituting the Saranima was p and the n-side cladding layer may be a superlattice of _{Al x Ga 1-x N /} GaN.
[0015]
In the nitride semiconductor laser device of the present invention, self-excited oscillation is suppressed by weakening light confinement and reducing the light density so that light oozes out in the opposite concept. In order to realize this, the present invention has a structure in which the refractive indexes of the cladding layer and the light guide layer are made close to each other. For example, the Al mixed crystal ratio in the p and n cladding layers is reduced to such an extent that the threshold current density does not increase, or the Al mixed crystal ratio in the p and n light guide layers is increased. With this structure, the current value at which self-oscillation occurs can be increased, and the occurrence of self-oscillation can be suppressed.
[0016]
Further, the NFP width in the vertical direction is increased, and as a result, there is an advantage that the FFP width in the vertical direction can be reduced. NFP is called a near field pattern or near-field image, and refers to an intensity distribution image of laser light that appears on the reflection surface in both vertical and horizontal transverse modes. On the other hand, FFP is also called a far field pattern or far-field image, and refers to an intensity distribution image of laser light emitted sufficiently far from the reflecting surface. It can be said that NFP represents the light intensity distribution in the oscillation region, and FFP represents the properties of the light wave including the wave front and phase of the light. Since FFP indicates the spread of the emitted light, if the FFP width is small, the FFP θ angle converges and the spread decreases, and the user can easily handle the laser. As described above, the nitride semiconductor laser device of the present invention has an advantage that it can be an easily handled laser with a small FFP in addition to suppressing self-excited oscillation.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiment described below exemplifies a nitride semiconductor laser element for embodying the technical idea of the present invention, and the present invention does not specify the nitride semiconductor laser element as follows.
[0018]
Further, in this specification, in order to facilitate understanding of the scope of claims, the numbers corresponding to the members shown in the embodiments are referred to as “claims column” and “means for solving the problems”. It is added to the members shown in the column. However, the members shown in the claims are not limited to the members in the embodiments.
[0019]
The composition ratio X values of the general formula Al _X Ga _1-X N of the n-type layer, a p-type layer Al _X Ga _1-X N and the like described herein are merely illustrates the general formula, n X of the mold layer and X of the p-type layer do not show the same value. Similarly, for the Y values used in other general formulas, the same general formula does not indicate the same value.
[0020]
In the nitride semiconductor laser device of the present invention, the clad layer is an optical confinement layer including a nitride semiconductor having a refractive index smaller than that of the active well layer. Superlattice refers to a multilayer film structure in which nitride semiconductor layers having a single layer thickness of 100 angstroms or less and different compositions are laminated, preferably 70 angstroms or less, more preferably 40 angstroms or less. A nitride semiconductor layer is stacked. As a specific configuration, for example, a superlattice in which an Al _X Ga _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 stacked. and, 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 A superlattice can be formed by a combination of a ternary mixed crystal and a ternary mixed crystal such as Ga _1-Z N (0 <Z <1) or a ternary mixed crystal and a binary mixed crystal. Of these, a superlattice composed of Al _x Ga _1-x N and GaN is most preferred.
[0021]
Further, if the n-side cladding layer has the above-described configuration in order to confine light emission from the active layer, the p-side cladding layer can have the same configuration as the n-side cladding layer. However, when the p-side cladding layer is configured as in claim 1, it is desirable that the thickness of the p-side cladding layer is smaller than that of the n-side cladding layer. This is because when the Al average composition for the group 3 element 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 the threshold value increases as the resistance value of AlGaN increases. This is because there is a tendency.
[0022]
When the p-side cladding layer is a superlattice having a nitride semiconductor containing Al (however, in this case, the leakage of light is not involved, and the case where it merely acts as a cladding layer as carrier confinement) is used. It is desirable that the thickness of the entire layer is greater than the thickness of the entire p-side cladding layer. Similar to the n-side cladding layer, the nitride semiconductor layer constituting the p-side cladding layer is composed of, for example, an Al _x Ga ₁ -XN (0 <X <1) layer and its Al _x Ga _1-x N layer. A superlattice obtained by stacking other nitride semiconductor layers different from each other in Al _x Ga _1-x N / GaN, Al _x Ga _1-x N / Al _y Ga _1-y N (0 <Y <1, Y < X), the combination of the _{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 ternary mixed crystal and the binary mixed crystal And a superlattice composed of Al _x Ga _1-x N and GaN is most preferred.
[0023]
The Al average composition in the superlattice of the present invention is determined by the following calculation method. For example, in the case of a superlattice obtained by laminating 200 pairs (1.0 μm) of 25 Å Al _0.5 Ga _0.5 N and 25 Å GaN, one pair is 50 Å, the Al mixed crystal ratio with respect to the group III element of the layer containing Al Therefore, 0.5 · (25 μm / 50 μm) = 0.25, and the Al average composition in the group 3 element of the entire superlattice is 25%. On the other hand, when the film thicknesses are different, when Al _0.5 Ga _0.5 N is laminated at 40 angstroms and GaN is laminated at 20 angstroms, the weighted average of the film thicknesses is obtained and 0.5 (40/60) = 0.333, The Al average composition is 33.3%. That is, the superlattice Al in the present invention is obtained by multiplying the Al mixed crystal ratio of the single nitride semiconductor layer containing Al to the Group 3 element by the ratio of the nitride semiconductor layer to the thickness of one pair of superlattices. Average composition. The same applies to the case where both Al are included. For example, 0.1 (20/50) +0.2 (30/50) = 0.16 in the case of Al _0.1 Ga _0.9 N20 angstrom and Al _0.2 Ga _0.8 N30 angstrom. In other words, 16% is Al average composition. In the above example, AlGaN / GaN and AlGaN / AlGaN have been described. However, the same calculation method is applied to AlGaN / InGaN. Therefore, when growing the n-side cladding layer, the growth method can be designed based on the above calculation method. Further, the Al average composition of the n-side cladding layer can be detected using an analyzer such as SIMS (secondary ion mass spectrometer) or Auger.
[0024]
【Example】
FIG. 1 is a schematic cross-sectional view showing a main part of a laser device according to an embodiment of the present invention, and shows a cross section when cut in a direction perpendicular to a ridge stripe. Hereinafter, examples will be described with reference to this figure as necessary.
[0025]
[Example 1]
Hereinafter, the laser element produced as Example 1 will be described in order.
(Underlayer)
A heterogeneous substrate made of sapphire with a 2-inch φ, C-plane as the main surface is set in a MOVPE reaction vessel, the temperature is set to 500 ° C., trimethylgallium (TMG), ammonia (NH ₃ ) is used, and a buffer made of GaN A layer (not shown) is grown to a thickness of 200 angstroms. After the growth of the buffer layer, the temperature is set to 1050 ° C., and an underlying layer made of GaN is grown to a thickness of 4 μm. This underlayer functions as an underlayer for forming a protective film partially on the surface and then performing selective growth of the nitride semiconductor substrate. The underlayer is preferably grown with Al _x Ga _1-X N (0 ≦ X ≦ 0.5) having an Al mixed crystal ratio X value of 0.5 or less. If it exceeds 0.5, the crystal itself tends to crack rather than a crystal defect, so that the crystal growth itself tends to be difficult. Further, it is desirable to grow the film thickness to be thicker than the buffer layer and adjust the film thickness to 10 μm or less. In addition to sapphire, a substrate made of a material different from a nitride semiconductor, such as SiC, ZnO, spinel, GaAs, or the like, which is known for growing a nitride semiconductor, can be used.
[0026]
(Protective film)
After the underlayer growth, the wafer is taken out from the reaction vessel, a striped photomask is formed on the surface of the underlayer, and a protective film made of SiO _{2 having a} stripe width of 10 μm and a stripe interval (window portion) of 2 μm is formed by a CVD apparatus. It is formed with a film thickness of 1 μm. The shape of the protective film may be any shape such as a stripe shape, a dot shape, or a grid pattern, but the second nitride semiconductor layer with fewer crystal defects is formed by increasing the area of the protective film than the window portion. Easy to grow. Examples of the material for the protective film include silicon oxide (SiO _x ), silicon nitride (Si _x N _y ), titanium oxide (TiO _x ), zirconium oxide (ZrO _x ) and other oxides, nitrides, and multilayer films thereof. In addition, a metal having a melting point of 1200 ° C. or higher can be used. These protective film materials withstand the nitride semiconductor growth temperature of 600 ° C. to 1100 ° C., and have a property that the nitride semiconductor does not grow or hardly grow on the surface thereof.
[0027]
(Nitride semiconductor substrate)
After forming the protective film, the wafer is set again in the MOVPE reaction vessel, the temperature is set to 1050 ° C., and a nitride semiconductor substrate made of undoped GaN is grown to a thickness of 20 μm using TMG and ammonia. In the surface of the nitride semiconductor substrate after the growth, there are almost no crystal defects appearing in the central portion of the protective film and the central portion of the window portion, but many crystal defects are present in the initial stage of the growth. It tends to occur in the upper part of the window. Therefore, by preventing the ridge stripe from being related to the crystal defect when the ridge is formed in the subsequent laser element, the crystal defect is not dislocated in the active layer, and the reliability of the element is improved. The nitride semiconductor substrate can be grown using halide vapor phase epitaxy (HVPE), but can also be grown by MOVPE. The nitride semiconductor substrate is most preferably grown with GaN containing no In or Al. As the gas during growth, an organic gallium compound such as triethylgallium (TEG) is used in addition to TMG, and the nitrogen source is ammonia, or Most preferably, hydrazine is used. Further, the carrier concentration may be adjusted to an appropriate range by doping this GaN substrate with n-type impurities such as Si and Ge. In particular, when removing the heterogeneous substrate, the underlayer, and the protective film, the nitride semiconductor substrate serves as a contact layer, and therefore it is desirable to dope the nitride semiconductor substrate with n-type impurities.
[0028]
(N-side contact layer 11)
Next, an n-side contact layer 11 made of GaN doped with Si 3 × 10 ¹⁸ / cm ³ is grown to a thickness of 5 μm on the second nitride semiconductor layer using ammonia, TMG, and silane gas as an impurity gas. Let Further, when the heterogeneous substrate to the protective film are removed and the electrode is provided on the nitride semiconductor substrate, it can be omitted. The n-side contact layer 11 is a buffer layer grown at a high temperature. For example, GaN, AlN, etc. at a low temperature of 900 ° C. or lower on a substrate made of a material different from a nitride semiconductor body such as sapphire, SiC, spinel. Is distinguished from a buffer layer that is directly grown at a film thickness of 0.5 μm or less.
[0029]
(Crack prevention layer 12)
Next, a crack prevention layer 12 made of In _0.06 Ga _0.94 N is grown to a thickness of 0.15 μm using TMG, TMI (trimethylindium), and ammonia at a temperature of 800 ° C. This crack prevention layer can be omitted.
[0030]
(N-side cladding layer 13 = superlattice layer)
Subsequently, a first layer made of n-type Al _0.08 Ga _0.92 N doped with 1 × 10 ¹⁹ / cm ^{3 of} Si at 1050 ° C. using TMA, TMG, ammonia, and silane gas is grown to a thickness of 25 Å. Subsequently, the silane gas and TMA are stopped, and a second layer made of undoped GaN is grown to a thickness of 25 Å. Then, a superlattice layer is formed as first layer + second layer + first layer + second layer +..., And an n-side cladding layer 13 made of a superlattice having a total film thickness of 1.2 μm is grown. The n-side cladding layer made of this superlattice has an Al average composition of 4.0% with respect to Group 3 elements. In addition, when a superlattice in which nitride semiconductors having different band gap energies are stacked on the n-side cladding layer, the crystallinity tends to be improved when so-called modulation doping is performed by doping a large amount of impurities into one of the layers. However, both may be doped in the same way.
[0031]
(N-side light guide layer 14)
Subsequently, the silane gas is stopped, and an 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, and it is desirable to grow GaN and InGaN, and it is usually desirable to grow with a film thickness of 100 Å to 5 μm, more preferably 200 Å to 1 μm. .
[0032]
(Active layer 15)
Next, the active layer 14 is grown using TMG, TMI, and ammonia. The active layer is maintained at a temperature of 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 grown to a thickness of 100 Å at the same temperature only by changing the TMI molar ratio. A well layer and a barrier layer are stacked in order, and finally an active layer having a multi-quantum well structure (MQW) having a total thickness of 440 Å is grown by ending with the barrier layer. The active layer may be undoped as in this embodiment, or may be doped with n-type impurities and / or p-type impurities. Impurities may be doped into both the well layer and the barrier layer, or one of them may be doped.
[0033]
(P-side cap layer 16)
Next, the temperature is increased to 1050 ° C., TMG, TMA, ammonia, Cp ₂ Mg (cyclopentadienyl magnesium) is used, and the band gap energy is larger than that of the p-side light guide layer 17. Mg is 1 × 10 ²⁰ / A p-side cap layer 16 made of cm ³ doped p-type Al _0.3 Ga _0.7 N is grown to a thickness of 300 Å. When the p-type cap layer 16 is formed with a film thickness of 0.1 μm or less, the output of the element tends to be improved. The lower limit of the film thickness is not particularly limited, but it is desirable to form the film with a film thickness of 10 angstroms or more.
[0034]
(P-side light guide layer 17)
Subsequently, Cp ₂ Mg and TMA are stopped, and a p-side light guide layer 17 made of undoped GaN having a band gap energy smaller than that of the p-side cap layer 16 at 1050 ° C. is grown to a thickness of 0.1 μm. This layer acts as a light guide layer of the active layer, and is preferably grown by GaN and InGaN, similarly to the n-type light guide layer 14.
[0035]
(P-side cladding layer 18 = superlattice)
Subsequently, a third layer made of p-type Al _0.08 Ga _0.92 N doped with 1 × 10 ²⁰ / cm ³ Mg at 1050 ° C. was grown to a thickness of 25 Å, and then only TMA was stopped, and undoped GaN A fourth layer is grown to a thickness of 25 Å, and a p-side cladding layer 18 made of a superlattice layer having a total thickness of 0.6 μm is grown. This p-side cladding layer also has an Al average composition of 4.0%. In addition, when the p-side cladding layer is also made of a superlattice in which at least one of the nitride semiconductor layers containing Al is included and nitride semiconductor layers having different band gap energies are stacked, impurities are highly doped in any one of the layers. When so-called modulation doping is performed, the crystallinity tends to be improved, but both may be doped in the same manner.
[0036]
Here, the film thickness of the core portion (waveguide portion) sandwiched between the clad layers will be described. The core portion is a region where the n-side light guide layer 14, the active layer 15, the p-side cap layer 16, and the p-side light guide layer 17 are combined, that is, between the n-side cladding layer and the p-side cladding layer. A nitride semiconductor layer including an active layer, which is a region that guides light emission of the active layer. In the case of a nitride semiconductor laser element, the FFP does not become a single beam because, as described above, the light emitted from the cladding layer is guided in the n-side contact layer and becomes multimode. is there. In addition, there is a case where a multimode 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 light in the core with the cladding layer. However, if multi-mode is possible in the core, FFP will be disturbed. Therefore, in relation to the n-side cladding layer of the present invention, it is desirable to adjust the thickness of the core portion so as not to be multimode in the core. A preferable thickness for preventing multimode from occurring in the core portion is 200 angstrom or more and 1.0 μm or less, more desirably 500 angstrom to 0.8 μm, most desirably 0.1 μm to 0.5 μm. It is desirable to adjust to. If it is thinner than 200 angstroms, light leaks from the core part and the threshold tends to increase. If it is thicker than 1.0 μm, it tends to be multimode.
[0037]
(P-side contact layer 19)
Finally, a p-side contact layer 18 made of p-type GaN doped with 2 × 10 ²⁰ / cm ^{3 of} Mg is grown on the p-side cladding layer 18 at a temperature of 1050 ° C. to a thickness of 150 Å. The p-side contact layer 19 can be composed of p-type In _X Al _Y Ga _1-XY N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1). The most favorable ohmic contact with the electrode is obtained.
[0038]
The wafer on which the nitride semiconductor is grown as described above is annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the layer doped with the p-type impurity.
[0039]
After annealing, the wafer is taken out of the reaction vessel, and the uppermost p-side contact layer 18 and p-side cladding layer 17 are etched by an RIE apparatus to form a ridge shape having a stripe width of 4 μm as shown in FIG. . When forming a ridge stripe, the ridge stripe is formed at a position where no crystal defect appears on the surface of the nitride semiconductor substrate. In the case of FIG. 1, many crystal defects tend to appear at the center of the stripe-shaped window at the initial stage of growth. When stripes are formed at positions where there are almost no crystal defects in this way, the crystal defects tend not to extend to the active layer, so that the device can have a long life and reliability is improved.
[0040]
Next, a mask is formed on the ridge surface, and etching is performed by RIE to expose the surface of the n-side contact layer 11. The exposed n-side contact layer 11 also functions as a contact layer for forming the n-electrode 23.
[0041]
Next, a p-electrode made of Ni and Au is formed in a stripe shape on the ridge outermost surface of the p-side contact layer 19, while a stripe-like shape is formed on the surface of the n-side contact layer 11 where the n-electrode made of Ti and Al is exposed. 1, an insulating film made of SiO ₂ is formed on the surface of the nitride semiconductor layer exposed between the p-electrode and the n-electrode as shown in FIG. 1, and the p-electrode is electrically connected to the p-electrode through the insulating film. Connected p-pad electrodes are formed.
[0042]
As described above, after polishing the sapphire substrate of the wafer on which the n-electrode and the p-electrode are formed to 70 μm, the substrate is cleaved in a bar shape from the substrate side in a direction perpendicular to the stripe-shaped electrode, A resonator is manufactured. A dielectric multilayer film made of SiO ₂ and TiO ₂ is formed on the resonator surface, and finally a bar is cut in a direction parallel to the p-electrode to form a laser element.
[0043]
When this laser element was placed on a heat sink and each electrode was wire-bonded and laser oscillation was attempted at room temperature, it showed continuous oscillation at room temperature. The single laser beam had a single FFP and its shape was elliptical. A good shape was obtained.
[0044]
[Example 2]
In Example 1, when the n-side cladding layer 13 is grown, an n-side cladding made of a superlattice having a total thickness of 1.0 μm is formed by stacking Si-doped n-type Al _0.06 Ga _0.94 N25 angstroms and undoped GaN 25 angstroms A laser device was fabricated in the same manner except that the layer 13 was grown. The n-side cladding layer has an Al average composition of 3%. This laser element also had almost the same characteristics as in Example 1.
[0045]
[Example 3]
In Example 1, when the n-side cladding layer 18 is grown, the Si-doped n-type Al _0.07 Ga _0.93 N layer 25 Å and the undoped GaN layer 25 Å are grown in a total thickness of 1.4 μm. Thus, a laser element was produced. The n-side cladding layer has an Al average composition of 3.5%. This laser device showed characteristics that a decrease in threshold and an improvement in life could be confirmed.
[0046]
The present invention also weakens the light confinement effect by bringing the difference in refractive index between the light guide layer and the cladding layer closer. Therefore, in addition to the method of lowering the Al mixed crystal ratio in the cladding layer, for example, it can be realized by a method of increasing the Al mixed crystal ratio by mixing Al in the guide layer. This method can be performed using a procedure substantially similar to that of the above-described embodiment.
[0047]
【The invention's effect】
As described above, the present invention has succeeded in reducing the light density and suppressing the self-excited oscillation by adopting a structure that weakens the light containment with the idea opposite to the conventional one. That is, in the past, the purpose was to confine light, but with this method, the light density was high and self-oscillation was likely to occur. In the present invention, conversely, by adjusting the Al mixed crystal ratio to intentionally weaken the light confinement and make the light leak, the self-excited oscillation can be controlled and the FFP in the vertical direction can be reduced. Realized the features.
[0048]
The nitride semiconductor laser device of the present invention has a structure that suppresses the light confinement effect by bringing the difference in refractive index between the cladding layer and the light guide layer closer. Optical confinement effect, the cladding layer, varies by each of the difference in refractive index n _c and n _g of the optical guide layer. For example, the greater the difference in n, the greater the confinement effect. Conversely, the smaller the difference of n, the smaller the confinement effect and the light density can be suppressed. However, if the difference is too close, the laser will not oscillate. In the present invention, by setting the Al mixed crystal ratio to an optimum value, laser oscillation is maintained and the Al mixed crystal ratio is reduced to such an extent that the threshold current density does not increase, thereby suppressing self-excited oscillation and reducing FFP. And a highly reliable semiconductor laser.
[0049]
In the present invention, the thickness of the n-side cladding layer is set to 1 μm to 2 μm in order to prevent ripples due to the influence of leaked light. When the p-electrode and the n-electrode are formed on the same surface side, the light emitted from the active layer leaks from the n-type cladding layer, and the leaked light is guided through the n-type contact layer having a large refractive index. A phenomenon of emission from the end face of the mold contact layer occurs. Although the detailed principle is not clear, when this weak light overlaps the main laser light emitted from the resonance surface, it is considered that the main laser light is rippled and the FFP becomes a small multimode. In order for the laser beam to function well, it is desirable to suppress the ripple from riding on the FFP.
[0050]
Utilizing the structure of the present invention has the effect of reducing the aspect ratio, and it is also possible to increase the output power that causes self-excited oscillation. For this reason, it becomes possible to produce a stable LD with high output, and it can be used as a laser used for DVD writing.
[Brief description of the drawings]
FIG. 1 is a perspective view showing the main structure of a laser device according to an embodiment of the present invention.
DESCRIPTION OF SYMBOLS 11 ... n side contact layer 12 ... crack prevention layer 13 ... n side clad 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

Claims (1)

Between the n-side and the p-side cladding layer with an average composition of Al of 0.02 to 0.04, a p- and n-side light guide layer and an active layer containing InGaN are formed,
The p and n side light guide layers have a nitride semiconductor layer containing at least Al,
And the average composition of Al contained in the p and n side light guide layers is a value smaller than that of the clad layer, and the film thicknesses are 0.1 μm to 0.2 μm, respectively.
The thickness of the core portion sandwiched between the clad layers is 200 angstroms or more and 1.0 μm or less,
A nitride semiconductor laser element, wherein a ridge stripe of the laser element is formed up to a region of the p-side light guide layer.

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