JP2004186708A - Gallium nitride semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gallium nitride semiconductor laser device being usable as a light source of an optical disk system and having good laser oscillation characteristics. <P>SOLUTION: The gallium nitride semiconductor laser device is equipped with an active layer comprising a nitride semiconductor sandwiched at least in between a cladding layer and/or guiding layer on a substrate. The length in a laser resonator direction of an ohmic electrode which provides current to the active layer is shorter than the length of the laser resonator, and the ohmic electrode is divided. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a gallium nitride based semiconductor laser device used as a light source of an optical disk system.

A gallium nitride-based semiconductor (GaInAlN) is used as a semiconductor material for a semiconductor laser device (LD) having an emission wavelength in the ultraviolet to green wavelength region. A semiconductor laser device using this gallium nitride-based semiconductor is described in, for example, Patent Document 1 below, and a perspective view thereof is shown in FIG. 8, 201 is a sapphire substrate, 202 is a GaN buffer layer, 203 is an n-GaN contact layer, 204 is an n-In _0.1 Ga _0.9 N layer, 205 is an n-Al _0.3 Ga _0.7 N cladding layer, and 206 is an n- A GaN guide layer, 207 is an active layer having a multiple quantum well structure composed of an In _0.2 Ga _0.8 N quantum well layer and an In _0.05 Ga _0.95 N barrier layer, 208 is a p-Al _0.2 Ga _0.8 N layer, and 209 is a p-GaN guide layer , 210 is a p-Al _0.3 Ga _0.7 N cladding layer, 211 is a p-GaN contact layer, 212 is a p-side electrode, and 213 is an n-side electrode. Here, the multi-quantum well structure active layer 207 is a total of 27 layers including 14 layers of 2.5 nm thick In _0.2 Ga _0.8 N quantum well layers and 13 layers of 5.0 nm thick In _0.05 Ga _0.95 N barrier layers. The quantum well layers and the barrier layers are formed alternately.

  In this conventional example, a stripe-shaped p-side electrode 212 and an n-side electrode 213 are formed on a wafer, and then a sapphire substrate is cleaved to produce a laser resonator. Each electrode is cut at the end face of the resonator. Thus, 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 in an optical disk system, the optical output is modulated even when a constant current is injected to prevent data read errors due to noise during data read. The self-sustained pulsation type semiconductor laser device described above is used. Such a semiconductor laser device is described in Patent Document 2 below, and a cross-sectional view thereof is shown in FIG. In FIG. 9, 221 is an n-SiC substrate, 222 is an n-AlN buffer layer, 223 is an n-Al _0.15 Ga _0.85 N clad layer, 224 is an In _0.15 Ga _0.85 N active layer having a thickness of 50 nm, and 225 is p-Al _0.15 Ga _0.85 N first p-type cladding layer, 226 is a p-In _0.2 Ga _0.8 N saturable absorbing layer, 227 is an n-Al _0.25 Ga _0.75 N current blocking layer, 228 is p-Al _0.15 Ga _0.85 N second p-type cladding Layers, 229 are p-GaN cap layers, 230 is a p-GaN contact layer, 231 is a p-side electrode, and 232 is an n-side electrode. In this conventional example, a part of the light generated in the active layer 224 is absorbed by the saturable absorption layer 226, so that the absorption coefficient of the saturable absorption layer 226 changes. The light emission intensity changes periodically. As a result, the coherence of the light emitted from the laser decreases. When a semiconductor laser device having such reduced coherence is used as a light source of an optical disk system, even if the light reflected by the disk returns to the semiconductor laser device, 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.

  However, a conventional semiconductor laser device using a gallium nitride-based semiconductor has the following problems. First, with respect to a self-pulsation type semiconductor laser device to which a saturable absorption layer is added, 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 is 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 added 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 no longer symmetric, and when condensing the emitted light using a lens, there has been a problem that the size of the focused spot cannot be made sufficiently small. .

On the other hand, in a conventional semiconductor laser device using a gallium nitride-based semiconductor without a saturable absorption layer, an increase in oscillation threshold current and a decrease in luminous efficiency as seen in a conventional self-pulsation type semiconductor laser device are observed. Although the problem that the focused spot size cannot be reduced does not occur, when this semiconductor laser element is used as a light source for an optical disk system, noise is generated by return light from the disk because self-excited oscillation does not occur. An error occurred. Therefore, there is a problem that a semiconductor laser device using a conventional gallium nitride-based semiconductor to which no saturable absorption layer is added cannot be practically used as a light source for an optical disk system.
JP-A-9-219560 JP-A-9-191160

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

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

  That is, the present invention provides a gallium nitride-based semiconductor laser device having, 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. A length of the ohmic electrode in the laser resonator direction that supplies the laser beam is shorter than the length of the laser resonator, and the ohmic electrode is divided, thereby providing a gallium nitride-based semiconductor laser device.

  Preferably, the ohmic electrode is divided by an insulating film.

  Preferably, the length of the ohmic electrode in the laser resonator direction is 100 μm or more and 500 μm or less.

  Preferably, 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 100 μm or less.

  The present invention also provides a gallium nitride-based semiconductor laser device having, 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. The present invention provides a gallium nitride based semiconductor laser device characterized in that the length of the supplied ohmic electrode in the laser resonator direction is shorter than the length of the laser resonator, and the laser device has self-excited oscillation characteristics.

  In the gallium nitride based semiconductor laser device according to the present invention, a region where current is not supplied is formed in a part of the active layer in the direction of the laser cavity, and light emission is guided in the region where current is not supplied. Light emission is absorbed, and as a result, it plays a role of a saturable absorption region, and can have self-pulsation characteristics. 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.

  A gallium nitride-based semiconductor laser device according to the present invention is a gallium nitride-based semiconductor laser device including at least a clad layer made of a nitride semiconductor and / or an active layer made of a nitride semiconductor sandwiched between guide layers. The length of the ohmic electrode for supplying current 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 into a part of the active layer in the laser resonator direction is formed. 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.

  In the present invention, since the ohmic electrode is divided, 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. The spot diameter when light is condensed by a lens can be reduced.

  When a gallium arsenide-based semiconductor material (AlGaAs) or an indium phosphide-based semiconductor material (InGaAsP) is used instead of the gallium nitride-based semiconductor material as in the present invention, the length of the electrode in the resonator direction is reduced. Even if the length is shorter than the length of the resonator, the injected current spreads in the semiconductor, and the current is injected into all the active layer regions, and the self-excited oscillation characteristics cannot be obtained. On the other hand, in the gallium nitride-based semiconductor material, since current spread hardly occurs due to a large electric resistance value, it was found that current was not injected into the semiconductor layer immediately below the region where no electrode was formed. Invented the invention.

  Furthermore, the nitride-based semiconductor laser device for realizing self-pulsation according to the present invention can be obtained by reducing the length of the electrode in the laser resonator direction by 1 μm to 100 μm with respect to the length of the laser resonator. it can. If the difference in length is shorter than 1 μm, it is difficult to obtain self-pulsation characteristics because the influence of the active layer serving as a saturable absorption region is small. 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.

  According to the present invention, the laser light is absorbed in the active layer in which the current is not injected, which is formed in a part of the laser cavity direction, and the oscillation threshold current density is slightly increased. Since the length of the semiconductor laser device is reduced, the oscillation threshold current itself does not increase, and a gallium nitride based semiconductor laser device having good laser oscillation characteristics can be obtained.

  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. Is preferably 100 μm or more and 500 μm or less. If it is smaller than 100 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 the 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, the density of electrons and holes existing in the active layer needs to be modulated at high speed. The system 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 the 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 a quantum well layer and a barrier layer are alternately stacked. The quantum well layer forming the active layer has a multiple quantum well structure in which the number of layers is 2 or more and 4 or less, and the thickness of the quantum well layer forming the active layer is 10 nm or less. It is easy to diffuse and the density of electrons and holes is easily modulated. 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 impeded that electrons and holes are uniformly distributed throughout the active layer. Therefore, it becomes difficult for electrons and holes to recombine. As a result, the laser characteristics of self-sustained pulsation deteriorate, but if the thickness of the barrier layer is 10 nm or less, holes and electrons are uniformly distributed in the active layer, which is favorable. A gallium nitride based semiconductor laser having excellent self-sustained pulsation characteristics was obtained.

Hereinafter, the present invention will be described in more detail according 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, and 5 is an n-GaN guide layer. , 6 is a multiple quantum well structure active layer comprising two In _0.2 Ga _0.8 N quantum well layers and one In _0.05 Ga _0.95 N barrier layer, 7 is an Al _0.2 Ga _0.8 N evaporation preventing layer, and 8 is a p- A GaN guide layer, 9 is a p-Al _0.1 Ga _0.9 Np-type clad 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 a SiO ₂ insulating film.

  In the present embodiment, by setting the length of the p-side electrode 11 in the laser resonator direction to 300 μm and the length of the laser resonator to 330 μm, the multiple quantum well corresponding to immediately below the ohmic electrode formed in the GaN-based semiconductor is formed. A current is supplied only to the region of the well structure active layer, and the region of the multiple quantum well structure active layer corresponding to the region where no electrode is formed functions as a saturable absorption region. A 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. Further, not limited to a sapphire substrate, a GaN substrate, a SiC substrate, a spinel substrate, an MgO substrate, a Si substrate, and a GaAs substrate can also be used. In particular, in the case of a GaN substrate and a SiC substrate, a good crystalline film having a small lattice constant difference from a gallium nitride-based semiconductor material laminated on a substrate is obtained as compared with a sapphire substrate, and the film is easily cleaved. There is an advantage that the resonator end face can be easily formed. The buffer layer 2 is not limited to GaN as long as a gallium nitride-based semiconductor can be epitaxially grown thereon, and another material such as AlN or AlGaN ternary mixed crystal may be used.

The n-type cladding layer 4 and the p-type cladding layer 9 may be an AlGaN ternary mixed crystal having an Al composition other than Al _0.1 Ga _0.9 N. 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. Further, when 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 crystal in the n-type cladding layer 4 and the p-type cladding layer 9 may not be the same.

  If the energy gap of the guide layers 5 and 8 is a material having 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, GaN is used. Instead, other materials, for example, InGaN, AlGaN ternary mixed crystal, InGaAlN quaternary mixed crystal, or the like may be used. 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 a guide layer, and functions as a semiconductor laser device.

The composition of the two In _0.2 Ga _0.8 N quantum well layers and one In _0.05 Ga _0.95 N barrier layer constituting the multiple quantum well structure active layer 6 may be set according to the required laser oscillation wavelength. To increase the oscillation wavelength, the In composition of the quantum well layer is increased. To shorten the oscillation wavelength, the In composition of the quantum well layer is decreased. The quantum well layer and the barrier layer may be quaternary or higher mixed crystal semiconductor containing other elements in trace amounts in the InGaN _3-element mixed crystal. Further, the In _0.05 Ga _0.95 N 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 that. Therefore, as long as it protects the quantum well layer, it can be used as the evaporation prevention layer 7, and AlGaN ternary mixed crystal or GaN having another Al composition may be used. The evaporation preventing layer 7 may be doped with Mg. In this case, there is an advantage that holes are easily injected from the p-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 manufacturing 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, but any growth method capable of epitaxially growing GaN may be used, such as MBE (molecular beam epitaxial growth) or HVPE (hydride vapor phase epitaxy). Other vapor phase epitaxy methods such as the above method can also be used.

First, trimethylgallium (TMG) and ammonia (NH ₃ ) are used as raw materials on a sapphire substrate 1 having a c-plane as a surface and set at a growth temperature of 550 ° C. The buffer layer 2 is grown to 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. Further continued trimethylaluminum (TMA) was added to raw materials, the growth temperature to grow a thickness of 0.7μm of Si-doped n-Al _0.1 Ga _0.9 Nn type cladding layer 4 remain 1050 ° C.. Subsequently, the supply of TMA is stopped, and the Si-doped n-GaN guide layer 5 having a thickness of 0.05 μm is grown with the growth temperature kept at 1050 ° C.

Next, the growth temperature is lowered to 750 ° C., and TMG, NH ₃ , and trimethylindium (TMI) are used as raw materials, and an In _0.2 Ga _0.8 N quantum well layer (5 nm thick) and an In _0.05 Ga _0.95 N barrier layer ( A multiple quantum well structure active layer (total thickness 15 nm) 6 is formed by sequentially growing an In _0.2 Ga _0.8 N quantum well layer (thickness 5 nm) and an In _0.2 Ga _0.8 N quantum well layer (thickness 5 nm). Further, 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 is raised again to 1050 ° C., and a 0.05 μm-thick Mg-doped p-GaN guide layer is formed using TMG, NH ₃ , and biscyclopentadienyl magnesium (Cp ₂ Mg) as raw materials. Grow 8. Subsequently, TMA is added to the raw material, and a 0.7 μm-thick Mg-doped p-Al _0.1 Ga _0.9 Np-type clad layer 9 is grown at a growth temperature of 1050 ° C. Subsequently, the TMA is removed from the raw material, and the Mg-doped p-GaN p-type contact layer 10 having a thickness of 0.2 μm is grown at a growth temperature of 1050 ° C. to complete a gallium nitride-based semiconductor wafer. Thereafter, the gallium nitride-based semiconductor wafer is annealed in a nitrogen gas atmosphere at 800 ° C. to lower the resistance of the Mg-doped p-type layer.

Further, using normal photolithography and dry etching techniques, etching is performed from the outermost surface of the p-GaN p-type contact layer 10 in the form of a 200 μm-wide stripe until the n-GaN n-type contact layer 3 is exposed, thereby forming a mesa structure. I do. Next, using the same photolithography and dry etching techniques as described above, the p-GaN p-type contact layers 10 and p are formed so as to form a 2 μm-wide ridge stripe on the outermost surface of the remaining p-GaN p-type contact layer 10. Part of the Al _0.1 Ga _0.9 Np type cladding layer 9 is etched. Subsequently, a 200 nm-thick SiO ₂ insulating film 13 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, on the surfaces of the SiO ₂ insulating film 13 and the ridge stripe 14, 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 300 μm. A rectangular p-side electrode 11 made of nickel and gold is formed at an interval of p-electrode distance Dp = 50 μm, and the surface of the n-GaN n-type contact layer 3 exposed by etching is used as a laser resonator of the n-side electrode. An n-side electrode 12 made of titanium and aluminum is formed in a rectangular shape having a width Wn = 150 μm in a vertical direction and a width Ln = 300 μm in a direction parallel to the laser resonator of the n-side electrode at an interval of Dn = 50 μm. Then, a gallium nitride-based semiconductor wafer is completed. 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 so as to be arranged.

  Then, in order to form a resonator of the semiconductor laser device in a direction perpendicular to the ridge stripe 14 by using the wafer, a region where the ohmic electrode is not formed (the interval Dp) by using a normal photolithography method and a dry etching method. 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. 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 excellent laser characteristics of an oscillation wavelength of 410 nm and an oscillation threshold current of 30 mA. In the semiconductor laser device of this embodiment, the length of the ohmic electrode in the resonator direction is made shorter by 30 μm than the length of the resonator of the semiconductor laser device, so that the active layer corresponding to the region where the electrode is not formed is formed. Since the region described above functions as a saturable absorption region, self-excited oscillation was also confirmed. 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 cavity end face of the semiconductor laser device is formed by dry-etching a region where no electrode is formed in order to form the cavity end face. 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 where the electrode material can be etched, and as a result, the reflection of laser light occurs. There has been a problem that the rate decreases and the threshold current for laser oscillation increases. When the portion where the electrode is not formed is etched as in this 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. In this embodiment, the resonator surface is formed by dry etching after forming the electrode. However, 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, If the difference from the length of the laser resonator is 1 μm or more and 100 μm or less, 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 set to 15 μm. However, the distances L1 and L2 do not need to be the same, and 1 μm or more from at least one of the resonator surfaces. It suffices if there is a region where no electrode is formed.

  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 5 nm, but these layer thicknesses 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 of 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 GaN or SiC having n-type conductivity is formed. , Si, GaAs or the like may be used for the substrate, the n-side electrode 12 may be formed on the back surface of the substrate. In this case, it is not necessary to manufacture a stripe-shaped mesa structure having a width of 200 μm. If the length of the p-side electrode in the resonator direction is made shorter than the length of the resonator, the n-side electrode is entirely covered with the back surface. It may be formed in. Further, as the SiO ₂ insulating film 13 serving as the current blocking layer, another dielectric insulating film such as SiN or a semiconductor material having n-type conductivity or semi-insulating property may be used. The p-type and n-type structures of the nitride-based semiconductor may be reversed.

(Second embodiment)
First, a gallium nitride based semiconductor laser device wafer is 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, similarly to the first embodiment, as shown in FIG. 2, p-side electrodes 11 made of nickel and gold are formed in a rectangular shape with Wp = 150 μm and Lp = 300 μm at intervals of Dp = 50 μm. N-side electrodes 12 made of titanium and aluminum are formed in a rectangular shape with Wn = 150 μm and Ln = 300 μm at an interval of Dn = 50 μm.

  Thereafter, in order to form a cavity of the semiconductor laser device in a direction perpendicular to the ridge stripe 14, the laser cavity end face is formed by cleaving the wafer in a direction perpendicular to the ridge stripe 14 along a line AB. I do. FIG. 4 is a top view at the time of cleavage in the manufacturing process of the present invention. At this time, the distances L1 'and L2' between the electrode and the resonator surface are both 25 μm, and the resonator 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 excellent laser characteristics of an oscillation wavelength of 410 nm and an oscillation threshold current of 30 mA. Further, in the semiconductor laser device of the present embodiment, the length of the ohmic electrode in the resonator direction is made shorter by 50 μm than the length of the resonator of the semiconductor laser device, so that the active layer corresponding to the region where the electrode is not formed is formed. Since the region described above functions as a saturable absorption region, self-excited oscillation was also confirmed. 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.

  This embodiment utilizes the fact that the sapphire substrate can be cleaved by reducing its thickness to 100 μm or less. In this case, the sapphire substrate is very hard, so that a large load is applied to the portion to be cleaved. Need to be cleaved. 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. As a result, the electrodes may be electrically short-circuited, and the production yield of the semiconductor laser device is reduced. Therefore, it is preferable to cleave a portion where no electrode is formed to form a resonator surface.

  In the present embodiment, the length of the ohmic electrode in the laser resonator direction is set to 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 to 500 μm, If the difference from the length of the laser resonator is 1 μm or more and 100 μm or less, 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. However, it is not necessary that the distances L1 ′ and L2 ′ are equal, and at least one of the resonators is not required. It suffices if there is a region where the electrode is not formed at least 1 μm from the surface.

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

  Then, in order to form a resonator of the semiconductor laser device in a direction perpendicular to the ridge stripe, the laser cavity facet is formed by cleaving the wafer in a direction perpendicular to the ridge stripe along line CD. FIG. 5 shows a top view at the time of cleavage in the manufacturing process of the present invention. At this time, the lengths L5 and L6 of the electrodes are both 150 μm, and the resonator length L7 of the semiconductor laser element is 350 μm. Therefore, the difference between the length of the semiconductor laser resonator and the total length of the electrodes in the resonator direction is 50 μm. It is. 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 excellent laser characteristics of an oscillation wavelength of 410 nm and an oscillation threshold current of 30 mA. Further, in the semiconductor laser device of the present embodiment, the length of the ohmic electrode in the resonator direction is made shorter by 50 μm than the length of the resonator of the semiconductor laser device, so that the active layer corresponding to the region where the electrode is not formed is formed. Since the region described above functions as a saturable absorption region, self-excited oscillation was also confirmed. 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 electrode is formed is cleaved. However, a GaN substrate having a thickness of 50 μm is easily cleaved as compared with a sapphire substrate, so that it is not necessary to apply a large load. Even if the region in which is formed is cleaved, no deformation of the electrode occurs, and the production yield does not decrease. When the electrodes are formed up to the resonator surface as in the present embodiment, the transverse mode of the laser light is stabilized up to the resonator surface inside the semiconductor laser element, so that the astigmatism of the laser light is reduced. In addition, there is an advantage that the spot diameter when the laser beam is focused by the lens can be reduced. However, if the thickness of the GaN substrate is too large, a large load is required for cleavage, and if the thickness is large, electrodes are formed in the same manner as in the second embodiment to improve the production yield. It is preferable to form a cavity end face by cleaving an unoccupied region.

  In this embodiment, the sum of the lengths of the ohmic electrodes in the laser resonator direction is 300 μm, which is shorter than the length of the laser resonator by 50 μm, but the length of the ohmic electrodes in the laser resonator direction is 100 μm or more and 500 μm or less. If the difference from the length of the laser resonator is 1 μm or more and 100 μm or less, the same effect as in the present embodiment can be obtained. In the present embodiment, the lengths L5 and L6 of the two divided ohmic electrodes are set to the same 150 μm, but may be different from each other. 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 may be 100 μm or more and 500 μm or less, and the difference from the length of the laser resonator may be 1 μm or more and 100 μm or less.

  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 in which the n-side electrode was exposed by etching. In the above, the n-side electrode may be formed on the back side of the n-type GaN substrate. In this case, if the p-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)
As a current blocking layer formed on the side surface of the ridge stripe and the surface of the p-type layer other than the ridge stripe, instead of the SiO ₂ insulating film 13 used in the third embodiment, 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 example up to 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, stripes 21 made of a 10 μm wide SiO ₂ insulating film (200 nm thick) are formed at intervals of 290 μm in a direction perpendicular to the ridge stripes 14. FIG. 6 shows a top view of the gallium nitride based semiconductor laser device wafer at this time. Further, a p-side electrode 22 made of nickel and gold is formed on the surface of the stripe 21, the ridge stripe 14, and the Si-doped n-Al _0.25 Ga _0.75 N layer 15, and titanium is formed on the n-GaN n-type contact layer exposed by etching. An n-side electrode 23 made of aluminum is formed.

  Thereafter, in order to fabricate a laser cavity in a direction perpendicular to the ridge stripe 14, the laser cavity end face is formed by cleaving the wafer along a line EF in a direction perpendicular to the ridge stripe. 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 resonator surface are both 145 μm, and the resonator 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 has excellent 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 stripe 21 made of the SiO ₂ insulating film is formed, No current is injected into the 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, since the region of the active layer corresponding to the region where the stripe 21 is formed functions as a saturable absorption region, it was also confirmed that the semiconductor laser device oscillates 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, which is shorter than the length of the laser resonator by 10 μm. However, the length of the ohmic electrode in the laser resonator direction is 100 μm or more and 500 μm or less. If the difference from the length of the laser resonator is 1 μm or more and 100 μm or less, the same effect as in the present embodiment can be obtained. In the present embodiment, the distances L8 and L9 in the resonator direction of the two divided electrodes are both set to 145 μm. However, the distances L8 and L9 do not need to be the same distance, and 1 μm from at least one of the resonator surfaces. It suffices if there is a region where an electrode having a thickness of 100 μm or less is not formed. Further, the cleavage for forming the end face of the laser resonator may be performed by the stripe 21.

  Further, in this embodiment, an insulating GaN substrate is used, but the n-side electrode is formed on the surface of the n-GaN contact layer exposed by etching. However, if GaN having n-type conductivity is used for the substrate, Alternatively, an n-side electrode may be formed on the back surface of this 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.

1 is a perspective view showing a semiconductor laser device according to a first example 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. 3 is a top view illustrating a manufacturing process of the semiconductor laser device according to the first embodiment of the present invention. FIG. 9 is a top view illustrating a manufacturing process of the semiconductor laser device according to the second embodiment of the present invention. FIG. 11 is a top view illustrating a manufacturing process of the semiconductor laser device according to the third embodiment of the present invention. FIG. 13 is a top view illustrating a manufacturing process of the semiconductor laser device according to the fourth embodiment of the present invention. FIG. 13 is a top view illustrating a manufacturing process of the semiconductor laser device according to the fourth embodiment of the present invention. It is a perspective view which shows the conventional semiconductor laser element. FIG. 4 is a cross-sectional view showing a conventional self-pulsation type gallium nitride based semiconductor laser device.

Explanation of reference numerals

Reference Signs List 1 sapphire substrate, 2 GaN buffer layer, 3 n-GaN n-type contact layer, 4 n-Al _0.1 Ga _0.9 N n-type clad layer, 5 n-GaN guide layer, 6 multiple quantum well structure active layer, 7 Al _0.2 Ga _0.8 N Evaporation prevention layer, 8 p-GaN guide layer, 9 p-Al _0.1 Ga _0.9 Np-type clad 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 (5)

  In a gallium nitride-based semiconductor laser device comprising a substrate and 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, the ohmic electrode for supplying a current to the active layer is provided. A gallium nitride based semiconductor laser device, wherein a length in a laser resonator direction is shorter than a length of the laser resonator, and the ohmic electrode is divided.   The gallium nitride-based compound semiconductor laser device according to claim 1, wherein the ohmic electrode is divided by an insulating film.   The gallium nitride-based compound semiconductor laser device according to claim 1, wherein a length of the ohmic electrode in a laser resonator direction is 100 μm or more and 500 μm or less.   The gallium nitride based semiconductor laser device according to claim 1, wherein a difference between a length of the ohmic electrode in a laser resonator direction and a length of the laser resonator is 1 μm or more and 100 μm or less.   In a gallium nitride-based semiconductor laser device comprising a substrate and 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, the ohmic electrode for supplying a current to the active layer is provided. A gallium nitride based semiconductor laser device, wherein a length in a laser resonator direction is shorter than a length of the laser resonator, and the laser device has a self-excited oscillation characteristic.

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