JPH11340573A - Gallium nitride based semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser element, having a good laser ocsillation characteristic which is capable of being used as a light source of an optical disc system. SOLUTION: In a gallium nitride based semiconductor laser element having an activated layer 6, comprising a semiconductor nitride formed between at least clad layers 4 and 9, and/or guide layers 5 and 8, on a substrate 1, a length in a direction of a laser resonator of an ohmic electrode 11 which supplies current to the activated layer, is shorter than the length of the laser resonator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium nitride based semiconductor laser device used as a light source in an optical disk system.

[0002]

2. Description of the Related Art As a semiconductor material of a semiconductor laser device (LD) having an emission wavelength in the ultraviolet to green wavelength range,
Gallium nitride based semiconductor (GaInAlN) is used. A semiconductor laser device using this gallium nitride-based semiconductor is described in, for example, Japanese Patent Application Laid-Open No. 9-219560, and a perspective view thereof is shown in FIG. In FIG.
201 is a sapphire substrate, 202 is a GaN buffer layer,
203 is an n-GaN contact layer, 204 is n-In
_0.1 Ga _0.9 N layer, 205 is n-Al _0.3 Ga _0.7 N cladding layer, 206 is n-GaN guide layer, 207 is In _0.2
A multiple quantum well structure active layer comprising a Ga _0.8 N quantum well layer and an In _0.05 Ga _0.95 N barrier layer, 208 is p-Al _0.2
Ga _0.8 N layer, 209 is a p-GaN guide layer, 210 is a p-Al _0.3 Ga _0.7 N cladding layer, 211 is p-GaN
A contact layer 212 is a p-side electrode, and 213 is an n-side electrode. Here, the multiple quantum well structure active layer 207 includes:
5nm In _0.2 Ga _0.8 N quantum well layers 14 layers thick, 5.
A total of 27 layers of 13 In _0.05 Ga _0.95 N barrier layers having a thickness of 0 nm are formed, and quantum well layers and barrier layers are formed alternately.

In this conventional example, a striped p-side electrode 2 is formed.
After forming 12 and the n-side electrode 213 on the wafer, the sapphire substrate is cleaved to produce a laser resonator.
Each electrode was cut off at the end face of the resonator, and the length of each electrode in the resonator direction was equal to the length of the laser resonator.

On the other hand, when a semiconductor laser device using a gallium nitride-based semiconductor is used as a light source for an optical disk system, in order to prevent a data reading error due to noise at the time of reading data, the optical output is not increased even if a constant current is injected. A self-sustained pulsation type semiconductor laser device in which is modulated is used. Such a semiconductor laser device is described in JP-A-9-191160, and a cross-sectional view thereof is shown in FIG. In FIG. 9, 221 is n-SiC
Substrate, 222 is n-AlN buffer layer, 223 is n-A
l _0.15 Ga _0.85 N clad layer, 224 is a 50 nm thick In _0.15 Ga _0.85 N active layer, 225 is p-Al _0.15 Ga
_0.85 N first p-type cladding layer, 226 is p-In _0.2 Ga
_0.8 N saturable absorption layer, 227 is n-Al _0.25 Ga _0.75 N
The current blocking layer 228 is p-Al _0.15 Ga _0.85 N second
p-type cladding layer, 229 is a p-GaN cap layer, 23
0 is a p-GaN contact layer, 231 is a p-side electrode, 23
2 is an n-side electrode. In this conventional example, the active layer 22
4 is absorbed by the saturable absorption layer 226, thereby changing the absorption coefficient of the saturable absorption layer 226, and the emission intensity of the laser oscillation from the active layer 224 periodically changes. I do. As a result, the coherence of the light emitted from the laser decreases. When the semiconductor laser element having reduced coherence is used as a light source of an optical disk system, even if the light reflected from the disk returns to the semiconductor laser element, the emitted light from the laser and the return light due to reflection do not cause interference. Therefore, generation of noise is suppressed, and a data reading error can be prevented.

[0005]

However, a conventional semiconductor laser device using a gallium nitride based semiconductor has the following problems. First, as for a self-pulsation type semiconductor laser device having a saturable absorption layer, light generated from the active layer is absorbed by the saturable absorption layer, so that light loss inside the laser resonator increases. . As a result, there has been a problem that the oscillation threshold current of the semiconductor laser element increases and the luminous efficiency decreases. Further, in this conventional self-pulsation type semiconductor laser device, a saturable absorbing layer is added to only one of the cladding layers sandwiching the active layer, or a saturable absorbing layer is provided only to one of the guiding layers sandwiching the active layer. Because of the addition, the far-field pattern of the emitted light from the laser is not symmetrical, and when the emitted light is condensed using a lens, there has been a problem that the focused spot size cannot be sufficiently reduced. .

On the other hand, in a semiconductor laser device using a conventional gallium nitride-based semiconductor to which no saturable absorbing layer is added, an increase in oscillation threshold current and light emission as in a conventional self-sustained pulsation type semiconductor laser device are observed. The problem of reduced efficiency and the inability to reduce the size of the focused spot does not occur.However, if this semiconductor laser device is used as a light source for an optical disk system, self-oscillation does not occur, so noise is generated by the return light from the disk, and A read error occurred during reading. Therefore, there has been a problem that a conventional semiconductor laser device using a gallium nitride-based semiconductor without a saturable absorption layer cannot be practically used as a light source for an optical disk system.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and solves the problem of a gallium nitride based semiconductor laser device to provide a good laser oscillation characteristic which can be used as a light source for an optical disk system. It is an object to provide a gallium nitride based semiconductor laser device having the same.

[0008]

In order to find such an invention, the present inventors have studied in detail to solve the above-mentioned problems in the conventional device, and as a result, have found that the conventional self-sustained pulsation type semiconductor laser device. It has been found that a self-pulsation type semiconductor laser device can be obtained with a simple configuration without using the saturable absorption layer used.

That is, a gallium nitride based semiconductor laser device according to the present invention comprises a gallium nitride based semiconductor laser device having at least an active layer made of a nitride semiconductor sandwiched between a cladding layer and / or a guide layer. , The length of the ohmic electrode for supplying current to the active layer in the laser resonator direction is shorter than the length of the laser resonator. By making the length of the ohmic electrode in the laser resonator direction shorter than the length of the laser resonator, a region where current is not injected is formed in a part of the active layer in the laser resonator direction. At this time, since the laser light is guided even in the region where the current is not injected, the region where the current is not injected functions as a saturable absorption region for absorbing the laser light. The saturable absorption region allows the gallium nitride based semiconductor laser device to have self-pulsation characteristics. On the other hand, when current is injected into all regions of the active layer in the laser cavity direction as used in a conventional gallium nitride based semiconductor laser, no saturable absorption region is formed, and Excitation oscillation characteristics were not obtained.

Further, instead of the gallium nitride-based semiconductor material as in the present invention, a gallium arsenide-based semiconductor material (AlG
aAs) or indium phosphide-based semiconductor material (InGaAs)
When P) is used, the injected current spreads in the semiconductor even if the length of the electrode in the resonator direction is shorter than the length of the resonator, and the current is injected into all the active layer regions. As a result, self-excited oscillation characteristics could not be obtained. On the other hand, in the case of gallium nitride based semiconductor materials, since current spread hardly occurs due to a large electric resistance value, it has been found that current is not injected into the semiconductor layer immediately below the region where no electrode is formed. Invented the invention.

Further, according to the nitride semiconductor laser device for realizing self-sustained pulsation of the present invention, the length of the electrode in the laser resonator direction is 1 μm to 100 μm with respect to the length of the laser resonator.
It was obtained by shortening by m. If the difference in length is shorter than 1 μm, the effect of the active layer serving as the saturable absorption region is small, and no self-excited oscillation characteristics can be obtained. If the difference in length is longer than 100 μm, the influence of the active layer serving as a saturable absorption region increases, and hysteresis occurs in the optical output-current characteristics of the semiconductor laser device, so that the semiconductor laser device can be used in an optical disk system. Disappears.

In the present invention, although the active layer formed in a part in the laser cavity direction where the current is not injected causes a slight increase in the oscillation threshold current density due to the absorption of the laser beam, the current injection is performed. Since the length in the resonator direction is shortened, the oscillation threshold current itself does not increase, and a gallium nitride based semiconductor laser device having good laser oscillation characteristics can be obtained.

Further, in order to obtain a sufficiently large laser gain so that the nitride-based compound semiconductor laser device of the present invention oscillates, an active layer region into which current is injected needs to have an appropriate length. The ohmic electrode length is 10
It is desirable that the thickness be 0 μm or more and 500 μm or less. 10
If the diameter is smaller than 0 μm, a sufficiently large laser gain cannot be obtained, so that the oscillation threshold current value of the semiconductor laser element increases. Conversely, if it is larger than 500 μm, the region where current is injected into the active layer becomes longer. There is a problem that the oscillation threshold current value increases.

Further, the electrode whose length in the laser resonator direction is shorter than the length of the laser resonator is preferably a p-side electrode. This is because the p-type nitride-based compound semiconductor has a higher electric resistance than the n-type nitride-based compound semiconductor, so that the injected current can be more reliably prevented from spreading in the gallium nitride-based semiconductor, and saturable absorption can be prevented. This is because the region can be formed more reliably. Further, both the p-side electrode and the n-side electrode may be shorter than the length of the laser resonator.

Further, in order to obtain a self-pulsation type semiconductor laser as in the present invention, it is necessary to modulate the density of electrons and holes existing in the active layer at a high speed. The resulting gallium nitride-based semiconductor material has a large decrease in the mobility of electrons and holes due to the large effective mass of both electrons and holes and the presence of many crystal defects. Therefore, even if electrons and holes disappear due to radiative recombination, no new electrons and holes are injected by diffusion, and the density of electrons and holes is hardly modulated. Therefore,
As in the present invention, the active layer of the gallium nitride based semiconductor laser device is a single quantum well layer or a quantum well structure active layer in which quantum well layers and barrier layers are alternately stacked. The multi-quantum well structure in which the number of layers is 2 or more and 4 or less, and furthermore, by making the thickness of the quantum well layer forming the active layer 10 nm or less, electrons and holes are diffused in the entire active layer. This makes it easier to modulate the electron and hole densities. As a result, a gallium nitride based semiconductor laser device having stable self-sustained pulsation characteristics was obtained. In the case of an active layer having a multiple quantum well structure, if the thickness of the barrier layer forming the active layer is too large, it is difficult to uniformly distribute electrons and holes throughout the active layer. Therefore, it becomes difficult for electrons and holes to recombine. As a result, the laser characteristics of the self-sustained pulsation deteriorate, but if the thickness of the barrier layer is set to 10 nm or less, holes and electrons are uniformly distributed in the active layer. A gallium nitride based semiconductor laser having excellent self-sustained pulsation characteristics was obtained.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to specific examples. (First Embodiment) FIG. 1 is a perspective view showing a gallium nitride based semiconductor laser device according to a first embodiment of the present invention. In this figure, 1 is a sapphire substrate having a c-plane as a surface, 2 is a GaN buffer layer, 3 is an n-GaN n-type contact layer, 4 is an n-Al _0.1 Ga _0.9 Nn-type cladding layer,
5 is an n-GaN guide layer, 6 is a two-layer In _0.2 Ga _0.8 N
A multiple quantum well structure active layer comprising a quantum well layer and one In _0.05 Ga _0.95 N barrier layer, 7 is an Al _0.2 Ga _0.8 N evaporation preventing layer, 8 is a p-GaN guide layer, and 9 is p-Al _0.1 G
a _0.9 Np-type cladding layer, 10 is a p-GaN p-type contact layer, 11 is a p-side electrode, 12 is an n-side electrode, and 13 is Si
O ₂ insulating film.

In this embodiment, the length of the p-side electrode 11 in the laser resonator direction is set to 300 μm, and the length of the laser resonator is set to 330 μm, so that the p-side electrode 11 can be formed just below the ohmic electrode on the GaN-based semiconductor. Current is supplied only to the region of the multi-quantum well structure active layer, and the region of the multi-quantum well structure active layer corresponding to the region where no electrode is formed functions as a saturable absorption region, and thus has a self-excited oscillation characteristic. A nitride-based compound semiconductor laser device was obtained.

In the present invention, the surface of the sapphire substrate 1 may have another plane orientation such as a plane, r plane, or m plane. Not only sapphire substrate but also GaN substrate, SiC
Substrate, spinel substrate, MgO substrate, Si substrate, GaAs
Substrates can also be used. In particular, in the case of a GaN substrate and a SiC substrate, a good crystalline film having a small difference in lattice constant from a gallium nitride-based semiconductor material laminated on a substrate is obtained as compared with a sapphire substrate, and is easily cleaved. There is an advantage that the resonator end face can be easily formed. The buffer layer 2 is made of G if a gallium nitride based semiconductor can be epitaxially grown thereon.
Other materials regardless of aN, such as AlN and AlGaN
A ternary mixed crystal may be used.

N-type cladding layer 4 and p-type cladding layer 9
Is AlGaN having an Al composition other than Al _0.1 Ga _0.9 N
A ternary mixed crystal may be used. In this case, when the Al composition is increased, the energy gap difference and the refractive index difference between the active layer and the cladding layer increase, and carriers and light are effectively confined in the active layer, further reducing the oscillation threshold current value and improving the temperature characteristics. Can be achieved. Also, if the Al composition is reduced to such an extent that the confinement of carriers and light is maintained, the mobility of carriers in the cladding layer increases, and thus there is an advantage that the device resistance of the semiconductor laser device can be reduced. Further, these cladding layers may be quaternary or higher mixed crystal semiconductors containing trace amounts of other elements, and the composition of the mixed crystals in the n-type cladding layer 4 and the p-type cladding layer 9 may not be the same.

The guide layers 5 and 8 are made of a material whose energy gap has a value between the energy gap of the quantum well layer constituting the multiple quantum well structure active layer 6 and the energy gap of the cladding layers 4 and 9. If so, other materials such as InGaN, AlGaN ternary mixed crystal, InGaAlN quaternary mixed crystal, etc. may be used without being limited to GaN. Further, it is not necessary to dope the entire guide layer with a donor or an acceptor, and only a part of the multiple quantum well structure active layer 6 side may be non-doped, and further, the entire guide layer may be non-doped. In this case, there are advantages that the number of carriers existing in the guide layer is reduced, light absorption by free carriers is reduced, and the oscillation threshold current can be further reduced. Further, a gallium nitride based semiconductor laser having no guide layer does not always need to have a guide layer and functions as a semiconductor laser device.

Two In _0.2 Ga _0.8 N quantum well layers and one In _0.05 Ga layer constituting the multiple quantum well structure active layer 6 are formed.
The composition of the _0.95 N barrier layer may be set according to the required laser oscillation wavelength. If it is desired to increase the oscillation wavelength, the In composition of the quantum well layer should be increased. Make it smaller. Further, the quantum well layer and the barrier layer may be a quaternary or higher mixed crystal semiconductor containing a trace amount of another element in an InGaN ternary mixed crystal. Further, In _0.05 Ga _0.95 N
The barrier layer may simply use GaN.

In this embodiment, the Al _0.2 Ga _0.8 N evaporation preventing layer 7 is formed so as to be in contact with the active layer 6 having a multiple quantum well structure. This is to prevent evaporation. Therefore, any material that protects the quantum well layer can be used as the evaporation prevention layer 7 and has a different Al composition.
N-ternary mixed crystal or GaN may be used. Further, the evaporation preventing layer 7 may be doped with Mg.
There is an advantage that holes are easily injected from the GaN guide layer 8 and the p-Al _0.1 Ga _0.9 Np type clad layer 9. Further, when the In composition of the quantum well layer is small, the quantum well layer does not evaporate even if the evaporation prevention layer 7 is not formed. The characteristics of the laser element are not impaired.

Next, a method for fabricating the gallium nitride based semiconductor laser will be described with reference to FIGS. In the following description, the case where the MOCVD method (metal organic chemical vapor deposition) is used is shown. However, any growth method capable of epitaxially growing GaN may be used. Other vapor phase epitaxy methods such as the method described above.

First, trimethylgallium (TMG) and ammonia (NH 3) are placed on a 350 μm thick sapphire substrate 1 having a c-plane as a surface, which is set in a predetermined growth furnace.
_{Using 3} ) as a raw material, a GaN buffer layer 2 is grown at a growth temperature of 550 ° C. to a thickness of 35 nm.

Next, the growth temperature is raised to 1050 ° C., and a 3 μm-thick Si-doped n-GaN n-type contact layer 3 is grown using TMG, NH ₃ , and silane gas (SiH ₄ ) as raw materials. Subsequently, trimethyl aluminum (TMA) was added to the raw material, and the growth temperature was 1050 ° C.
0.7 μm thick Si-doped n-Al _0.1 Ga
_{A 0.9} Nn-type cladding layer 4 is grown. Subsequently, the supply of TMA was stopped, and the growth temperature was kept at 1050 ° C. to achieve a thickness of 0.1 mm.
A 05 μm Si-doped n-GaN guide layer 5 is grown.

Next, the growth temperature was lowered to 750 ° C.
, NH ₃ , and trimethylindium (TMI) as raw materials, an In _0.2 Ga _0.8 N quantum well layer (5 n thick).
m), In _0.05 Ga _0.95 N barrier layer (5 nm thick), In
By sequentially growing a _0.2 Ga _0.8 N quantum well layer (thickness: 5 nm), a multiple quantum well structure active layer (total thickness of 1
5 nm) 6. Subsequently, using TMG, TMA and NH ₃ as raw materials, an Al _0.2 Ga _0.8 N evaporation preventing layer 7 having a thickness of 10 nm is grown at a growth temperature of 750 ° C.

Next, the growth temperature was raised again to 1050 ° C., and TMG, NH ₃ , and biscyclopentadienyl magnesium (Cp ₂ Mg) were used as raw materials to form a layer having a thickness of 0.050 mm.
A 5 μm Mg-doped p-GaN guide layer 8 is grown.
Subsequently, TMA was added to the raw material, and the growth temperature was 1050.
0.7 μm-thick Mg-doped p-Al _0.1 G at 100 ° C.
a _0.9 Np-type cladding layer 9 is grown. Continue, TMA
Was removed from the raw material, and the growth temperature was kept at 1050 ° C., and the Mg-doped p-GaN p-type contact layer 1 having a thickness of 0.2 μm was formed.
0 is grown to complete a gallium nitride based semiconductor wafer. Then, the gallium nitride based semiconductor wafer is
Anneal in a nitrogen gas atmosphere at 0 ° C. to lower the resistance of the Mg-doped p-type layer.

Further, the n-type p-GaN p-type contact layer 10 is stripped from the outermost surface of the p-GaN p-type contact layer 10 by a conventional photolithography and dry etching technique.
-Etching is performed until the GaN n-type contact layer 3 is exposed to form a mesa structure. Next, by using the same photolithography and dry etching techniques as described above, 2 μm is formed on the outermost surface of the remaining p-GaN p-type contact layer 10.
p-GaNp to form an m-width ridge stripe
A part of the p-type contact layer 10 and the p-Al _0.1 Ga _0.9 Np-type clad layer 9 is etched. Subsequently, an SiO ₂ insulating film 13 having a thickness of 200 nm is formed as a current blocking layer on the side surfaces of the ridge stripe and on the surface of the p-type layer other than the ridge stripe.

Further, the width Wp of the p-side electrode in the direction perpendicular to the laser resonator is 150 μm and the width Lp of the p-side electrode in the direction parallel to the laser resonator is formed on the surfaces of the SiO ₂ insulating film 13 and the ridge stripe 14. = P-side electrode 11 made of nickel and gold in a rectangular shape of 300 μm
= W = 150 μm in the direction perpendicular to the laser resonator of the n-side electrode on the surface of the n-GaN n-type contact layer 3 exposed by etching and formed in a direction parallel to the laser resonator of the n-side electrode. The n-side electrodes 12 made of titanium and aluminum are formed in a rectangular shape having a width Ln = 300 μm at an interval of n-side electrode distance Dn = 50 μm to complete a gallium nitride based semiconductor wafer. FIG. 2 shows a top view of the gallium nitride based semiconductor wafer at this time. In the semiconductor laser device wafer shown in FIG. 2, three semiconductor laser devices are arranged in a line.

Thereafter, in order to form a cavity of the semiconductor laser device on the wafer in a direction perpendicular to the ridge stripe 14, a region where the ohmic electrode is not formed (interval) by using a usual photolithography method and a dry etching method. Dp) is dry-etched to form a laser cavity end face. FIG. 3 is a top view at the time of performing dry etching in the manufacturing process of the present invention. At this time, the distances L1 and L2 between the electrode and the resonator end face are both 15 μm, and the length L3 of the region to be dry-etched is 20 μm. Subsequently, the gallium nitride-based semiconductor wafer is divided into individual laser chips. And
Each chip is mounted on a stem, each electrode is connected to a lead terminal by wire bonding, and a gallium nitride based semiconductor laser device is completed.

The semiconductor laser device manufactured as described above had good laser characteristics of an oscillation wavelength of 410 nm and an oscillation threshold current of 30 mA. In the semiconductor laser device of the present embodiment, the length of the ohmic electrode in the resonator direction is 30 μm longer than the length of the resonator of the semiconductor laser device.
By making the length as short as possible, the region of the active layer corresponding to the region where the electrode is not formed functions as a saturable absorption region, and it was also confirmed that self-sustained pulsation occurred. As a result, when the gallium nitride-based semiconductor laser device of this example was used for an optical disk system, a data read error could be prevented, and a practical gallium nitride-based semiconductor laser device could be realized.

In this embodiment, since the sapphire substrate is hard and difficult to be cleaved, the region where no electrode is formed is dry-etched to form the cavity end face to form the cavity end face of the semiconductor laser device. I have. When the electrode is cut at the cavity facet as in the prior art, the electrode material is hardly dry-etched, so that the cavity facet is roughened under the etching conditions that can etch the electrode material. There has been a problem that the rate decreases and the threshold current for laser oscillation increases. In the case where a portion where an electrode is not formed is etched as in the present embodiment, the above-described problem does not occur, and a resonator surface having a clean surface that can be used as a laser resonator surface is obtained. . Further, in the present embodiment, the resonator surface is formed by dry etching after forming the electrode, but the electrode may be formed after forming the resonator surface by dry etching.

In the present embodiment, the length of the ohmic electrode in the laser resonator direction is 300 μm, which is shorter than the length of the laser resonator by 30 μm. However, the length of the ohmic electrode in the laser resonator direction is 100 μm to 500 μm. And the difference from the length of the laser resonator is 1 μm or more and 1
When the thickness is not more than 00 μm, the same effect as in the present embodiment can be obtained. In this embodiment, the distances L1 and L2 between the resonator and the electrodes in the resonator direction are both 15 μm.
It is not necessary that 1 and L2 be the same distance, and it is sufficient if there is a region where no electrode is formed 1 μm or more from at least one of the resonator surfaces.

In this embodiment, the thicknesses of the quantum well layer and the barrier layer constituting the multiple quantum well structure active layer 6 are both 5n.
However, the thicknesses of these layers need not be the same and may be different. Further, if the thickness of each of the quantum well layer and the barrier layer is set to 10 nm or less, the same effect can be obtained with other layer thicknesses without being limited to the present embodiment. The number of quantum well layers in the multiple quantum well structure active layer 6 may be three or four, or may be a single quantum well structure active layer.

Further, in this embodiment, since sapphire, which is an insulator, is used as the substrate, the n-side electrode 12 is formed on the surface of the n-GaN n-type contact layer 3 exposed by etching, but has n-type conductivity. GaN, SiC,
If Si, GaAs, or the like is used for the substrate, the n-side electrode 12 may be formed on the back surface of the substrate. In this case, in particular, 2
It is not necessary to manufacture a stripe-shaped mesa structure having a width of 00 μm. If the length of the p-side electrode in the resonator direction is shorter than the length of the resonator, the n-side electrode can be formed on the entire back surface. I do not care. Furthermore, the current blocking layer of SiO
_{(2) The} insulating film 13 may be made of another dielectric insulating film such as SiN or a semiconductor material having n-type conductivity or semi-insulating property. The p-type and n-type configurations of the nitride semiconductor may be reversed.

(Second Embodiment) A gallium nitride based semiconductor laser device wafer is first manufactured in the same manner as in the first embodiment except that the thickness of sapphire used as a substrate is reduced to 100 μm. At this time, as shown in FIG. 2, Wp = 150 μm and Lp = 30 as in the first embodiment.
P-side electrode 11 made of nickel and gold in a rectangular shape of 0 μm
Are formed at intervals of Dp = 50 μm, and Wn = 150 μm
The n-side electrodes 12 made of titanium and aluminum are formed in a rectangular shape with m and Ln = 300 μm at intervals of Dn = 50 μm.

Thereafter, the wafer is cleaved along the line AB in the direction perpendicular to the ridge stripe 14 to form a semiconductor laser device resonator in the direction perpendicular to the ridge stripe 14. Form an end face. FIG. 4 is a top view at the time of cleavage in the manufacturing process of the present invention. At this time, the distance L between the electrode and the resonator surface
1 ′ and L2 ′ are both 25 μm, and the cavity length L4 of the semiconductor laser device is 350 μm. Subsequently, the gallium nitride-based semiconductor wafer is divided into individual laser chips. Then, each chip is mounted on a stem, each electrode is connected to a lead terminal by wire bonding, and a gallium nitride based semiconductor laser device is completed.

The semiconductor laser device manufactured as described above has good laser characteristics of an oscillation wavelength of 410 nm and an oscillation threshold current of 30 mA. In the semiconductor laser device of the present embodiment, the length of the ohmic electrode in the resonator direction is 50 μm larger than the length of the resonator of the semiconductor laser device.
By making the length as short as possible, the region of the active layer corresponding to the region where the electrode is not formed functions as a saturable absorption region, and it was also confirmed that self-sustained pulsation occurred. As a result, when the gallium nitride-based semiconductor laser device of this example was used for an optical disk system, a data read error could be prevented, and a practical gallium nitride-based semiconductor laser device could be realized.

In this embodiment, the thickness of the sapphire substrate is set to 1
Utilizing the fact that cleavage is possible by reducing the thickness to not more than 00 μm, in this case, since the sapphire substrate is very hard, it is necessary to apply a large load to the portion to be cleaved for cleavage. In the case where an electrode is formed in a portion to be cleaved, a large load is applied to the electrode, so that the electrode is deformed and protrudes from the cleavage plane. by this,
The electrodes may cause an electrical short circuit, which lowers the production yield of the semiconductor laser device. Accordingly, it is preferable to cleave the portion where the electrode is not formed to produce the resonator surface.

In this embodiment, the length of the ohmic electrode in the laser resonator direction is set to 300 μm and shorter than the length of the laser resonator by 50 μm. However, the length of the ohmic electrode in the laser resonator direction is set to 100 μm to 500 μm. And the difference from the length of the laser resonator is 1 μm or more and 1
When the thickness is not more than 00 μm, the same effect as in the present embodiment can be obtained. In this embodiment, the distances L1 ′ and L2 ′ between the resonator and the electrode in the resonator direction are both 25 μm.
It is not necessary that L1 ′ and L2 ′ be the same distance, and it is sufficient if there is a region where no electrode is formed at least 1 μm from at least one of the resonator surfaces.

(Third Embodiment) A substrate having a thickness of 50 μm
A gallium nitride based semiconductor laser device wafer is first manufactured in the same manner as in the first embodiment except that the insulating GaN substrate is used. At this time, as shown in FIG. 2, similarly to the first embodiment, Wp = 150 μm, Lp = 300 μm
A p-side electrode 11 made of nickel and gold is
formed at intervals of p = 50 μm, Wn = 150 μm, Ln
= 300 μm rectangular n-side electrodes 12 made of titanium and aluminum are formed at an interval of Dn = 50 μm.

Thereafter, in order to form a resonator of the semiconductor laser device in a direction perpendicular to the ridge stripe in the direction perpendicular to the ridge stripe, the laser cavity facet is cleaved along the line CD in a direction perpendicular to the ridge stripe. Form.
FIG. 5 shows a top view at the time of cleavage in the manufacturing process of the present invention. At this time, the electrode lengths L5 and L6 are both 150 μm.
m, and the resonator length L7 of the semiconductor laser element is 350 μm, so that the difference between the length of the resonator of the semiconductor laser and the total length of the electrodes in the resonator direction is 50 μm. continue,
The gallium nitride based semiconductor wafer is divided into individual laser chips. Then, each chip is mounted on a stem, each electrode is connected to a lead terminal by wire bonding, and a gallium nitride based semiconductor laser device is completed.

The semiconductor laser device manufactured as described above had good laser characteristics of an oscillation wavelength of 410 nm and an oscillation threshold current of 30 mA. In the semiconductor laser device of the present embodiment, the length of the ohmic electrode in the resonator direction is set to 50 μm from the length of the resonator of the semiconductor laser device.
By making the length as short as possible, the region of the active layer corresponding to the region where the electrode is not formed functions as a saturable absorption region, and it was also confirmed that self-sustained pulsation occurred. As a result, when the gallium nitride-based semiconductor laser device of this example was used for an optical disk system, a data read error could be prevented, and a practical gallium nitride-based semiconductor laser device could be realized.

In the present embodiment, the region where the electrodes are formed is cleaved. However, a GaN substrate having a thickness of 50 μm is cleaved more easily than a sapphire substrate, so that a large load must be applied. In addition, even if the region where the electrode is formed is cleaved, the electrode is not deformed, and the production yield does not decrease. When the electrodes are formed up to the cavity surface as in the present embodiment, the transverse mode of the laser beam is stabilized up to the cavity surface inside the semiconductor laser device, so that the astigmatism of the laser beam is reduced. In addition, there is an advantage that the spot diameter when the laser light is focused by the lens can be reduced. However, if the thickness of the GaN substrate is too large, a large load is required at the time of cleavage. Therefore, when the thickness is large, the electrodes are formed in the same manner as in the second embodiment in order to improve the production yield. It is preferable to form a cavity end face by cleaving a region that is not present.

In this embodiment, the total length of the ohmic electrode in the laser resonator direction is 300 μm, which is shorter than the length of the laser resonator by 50 μm. However, the length of the ohmic electrode in the laser resonator direction is 100 μm. More than 500
μm or less, and the difference from the length of the laser resonator is 1 μm
When the thickness is not less than 100 μm, the same effect as in the present embodiment can be obtained. Also, in the present embodiment, the lengths L5 and L6 of the two divided ohmic electrodes
Although the length is set to 0 μm, the lengths may be different. Further, the same effect can be obtained even when the ohmic electrode is divided into three. The length of the ohmic electrode in the laser resonator direction is 100 μm or more and 500 μm or less, and the difference from the length of the laser resonator is 1 μm or more and 100 μm.
It does not matter if it is below.

Furthermore, in this embodiment, since an insulating GaN substrate was used, the n-side electrode was formed on the surface of the n-GaN n-type contact layer where the n-side electrode was exposed by etching. The n-side electrode is n
It may be formed on the back side of the type GaN substrate. In this case p
If the side electrode has the shape shown in any of the first to third embodiments, it may be formed on the entire back surface of the n-type GaN substrate.

(Fourth Embodiment) The SiO ₂ insulating film 1 used in the third embodiment was used as a current blocking layer formed on the side surface of the ridge stripe and on the surface of the p-type layer other than the ridge stripe.
In place of 3, a 0.5 μm thick Si-doped n-Al
_A gallium nitride-based semiconductor laser device wafer was manufactured in the same manner as in the third embodiment until before the electrode forming step, except that the _0.25 Ga _0.75 N layer 15 was used.

Subsequently, on the surface of the gallium nitride based semiconductor laser device wafer, an SiO ₂ insulating film (thickness: 200 nm) having a width of 10 μm in a direction perpendicular to the ridge stripe 14.
Are formed at intervals of 290 μm. FIG. 6 shows a top view of the gallium nitride based semiconductor laser device wafer at this time. Further, the stripe 21, the ridge stripe 14, and the Si-doped n-Al _0.25 Ga _0.75 N
A p-side electrode 22 made of nickel and gold is formed on the surface of the layer 15, and an n-side electrode 23 made of titanium and aluminum is formed on the n-GaN n-type contact layer exposed by etching.
Is formed.

After that, in order to fabricate a laser resonator in a direction perpendicular to the ridge stripe 14,
Cleaving along the line EF in a direction perpendicular to the ridge stripe forms a laser cavity end face. FIG. 7 shows a top view of the gallium nitride based semiconductor laser device wafer at this time. At this time, the distances L8 and L9 between the stripe 21 and the cavity surface are both 145 μm, and the cavity length L10 of the semiconductor laser is 300 μm. Subsequently, the gallium nitride-based semiconductor wafer is divided into individual laser chips. Then, each chip is mounted on a stem, each electrode is connected to a lead terminal by wire bonding, and a gallium nitride based semiconductor laser device is completed.

The semiconductor laser device manufactured as described above had good laser characteristics such as an oscillation wavelength of 410 nm and an oscillation threshold current of 25 mA. In the semiconductor laser device of the present embodiment, since the p-GaN p-type contact layer is not in ohmic contact with the p-side electrode and the n-side electrode in the region where the stripes 21 made of the SiO ₂ insulating film are formed, No current is injected into this region. That is, the difference between the length of the electrode in ohmic contact with the gallium nitride based semiconductor layer in the resonator direction and the length of the laser resonator is reduced by 10 μm. Therefore, stripe 21
Since the region of the active layer corresponding to the region where is formed functions as a saturable absorption region, it was also confirmed that the semiconductor laser device oscillated by itself. As a result, when the gallium nitride-based semiconductor laser device of this example was used for an optical disk system, a data read error could be prevented, and a practical gallium nitride-based semiconductor laser device could be realized.

In the present embodiment, the length of the ohmic electrode in the laser resonator direction is 290 μm and is shorter by 10 μm than the length of the laser resonator. However, the length of the ohmic electrode in the laser resonator direction is 100 μm or more and 500 μm. And the difference from the length of the laser resonator is 1 μm or more and 1
When the thickness is not more than 00 μm, the same effect as in the present embodiment can be obtained. Further, in the present embodiment, the distances L8 and L9 in the resonator direction of the two divided electrodes are both 145 μm, but the distances L8 and L9 need not be the same distance, and at least one of the resonator surfaces is It suffices if there is a region where an electrode of 1 μm to 100 μm is not formed. Also,
Cleavage for forming laser cavity end face is stripe 2
You can go with 1.

Further, in this embodiment, an insulating GaN substrate is used, but an n-side electrode is formed on the surface of the n-GaN contact layer exposed by etching. , An n-side electrode may be formed on the back surface of the substrate. At this time, if at least the stripe 21 is formed in the shape shown in FIG. 7, the n-side electrode may be formed on the entire back surface of the substrate.

[0053]

As described above, in the gallium nitride based semiconductor laser device according to the present invention, a region to which no current is supplied is formed in a part of the active layer in the direction of the laser resonator. In the region where the light emission is not performed, the light emission is guided and absorbs the light emission. As a result, the light emission plays a role of a saturable absorption region, and has a self-excited oscillation characteristic. As a result, a gallium nitride-based semiconductor laser device having good laser oscillation characteristics and usable for an optical disk, which does not generate an error when reading data, can be realized.

[Brief description of the drawings]

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

FIG. 2 is a top view showing a manufacturing process of the semiconductor laser device according to the first embodiment of the present invention.

FIG. 3 is a top view illustrating a manufacturing process of the semiconductor laser device according to the first embodiment of the present invention.

FIG. 4 is a top view illustrating a manufacturing process of a semiconductor laser device according to a second embodiment of the present invention.

FIG. 5 is a top view illustrating a manufacturing process of a semiconductor laser device according to a third embodiment of the present invention.

FIG. 6 is a top view illustrating a manufacturing process of a semiconductor laser device according to a fourth embodiment of the present invention.

FIG. 7 is a top view illustrating a manufacturing process of a semiconductor laser device according to a fourth embodiment of the present invention.

FIG. 8 is a perspective view showing a conventional semiconductor laser device.

FIG. 9 is a sectional view showing a conventional self-pulsation type gallium nitride based semiconductor laser device.

[Explanation of symbols]

1 sapphire substrate 2 GaN buffer layer 3 n-Gann type contact layer 4 n-Al _0.1 Ga _0.9 Nn type cladding layer 5 n-GaN guide layer 6 multiple quantum well structure active layer 7 Al _0.2 Ga _0.8 N evaporation preventing layer 8 p- GaN guide layer 9 p-Al _0.1 Ga _0.9 Np-type cladding layer 10 p-GaN p-type contact layer 11 p-side electrode 12 n-side electrode 13 SiO ₂ insulating film 14 ridge stripe 15 Si-doped n-Al _0.25 Ga _0.75 N layer

Claims (8)

[Claims] 1. A gallium nitride-based semiconductor laser device comprising, on a substrate, at least an active layer made of a nitride semiconductor sandwiched between a clad layer and / or a guide layer made of a nitride semiconductor, wherein a current is applied to the active layer. A gallium nitride based semiconductor laser device, wherein the length of the supplied ohmic electrode in the laser resonator direction is shorter than the length of the laser resonator. 2. The difference between the length of the ohmic electrode in the laser resonator direction and the length of the laser resonator is 1 μm or more and 1 μm or more.
2. The gallium nitride based semiconductor laser device according to claim 1, wherein the thickness of the gallium nitride based semiconductor laser device is not more than 00 μm. 3. The gallium nitride based semiconductor laser device according to claim 1, wherein a length of the ohmic electrode in a laser resonator direction is not less than 100 μm and not more than 500 μm. 4. The gallium nitride based semiconductor laser device according to claim 1, wherein said ohmic electrode is a p-side electrode. 5. The gallium nitride based semiconductor laser device according to claim 1, wherein said active layer comprises a single quantum well layer. 6. The active layer comprises a quantum well structure active layer in which quantum well layers and barrier layers are alternately stacked, and the number of quantum well layers is 2 or more and 4 or less. The gallium nitride based semiconductor laser device according to claim 1. 7. The gallium nitride based semiconductor laser device according to claim 5, wherein the thickness of the quantum well layer forming the active layer is 10 nm or less. 8. The barrier layer forming the active layer has a thickness of:
The gallium nitride based semiconductor laser device according to claim 6, wherein the thickness is 10 nm or less.