JP2007173402A - Semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a highly reliable semiconductor laser device by reducing a temperature rise at an end face relative to a central part of a resonator without causing dispersion of metal elements from a pad electrode. <P>SOLUTION: The semiconductor laser device has a semiconductor laminated body 120 which has a current injection region composed of a stripe 109a formed above an active layer 105, a p-side ohmic electrode 141 formed on the semiconductor laminated body 120 so as to cover the stripe 109a, and the pad electrode 143 electrically connected with the p-side ohmic electrode 141 on the semiconductor laminated body 120. The semiconductor laminated body 120 includes the active layer 105, and is formed almost perpendicularly to the longitudinal direction of the stripe 109a while having the resonator provided with a pair of cleavage faces 160 arranged oppositely to each other. The pad electrode 143 is formed in a region excluding the upper side of the stripe 109a. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor laser device applicable to a high-density optical disk device, a laser display device, an illumination device, or the like.

  In recent years, research and development of a semiconductor laser device using a III-V nitride compound semiconductor (hereinafter simply referred to as a nitride semiconductor) among semiconductor laser devices has progressed, and a short wavelength light source for a high-density optical disk device. As a part, it has come to practical use.

  A nitride semiconductor laser device is usually formed on a substrate made of, for example, n-type gallium nitride (GaN) by a metal organic chemical vapor deposition (MOCVD) method, on an n-type cladding layer, an active layer, a p-type cladding layer, and a p-type. After forming the double heterostructure including the contact layer, a part of the formed p-type layer is processed as a ridge-shaped stripe portion to form a waveguide, and the region excluding the upper surface of the stripe portion is formed of an insulating film After covering, the p-side electrode is formed. Further, an n-side electrode is formed on the back surface of the substrate, and subsequently, a double heterostructure is cleaved at a predetermined crystal plane to form a resonator. Among these manufacturing processes, the p-side electrode forming method is particularly noted as a factor that greatly affects the performance, reliability, yield and the like of the semiconductor laser device, and various improvements have been added. For example, the configuration of the p-side electrode in the conventional nitride semiconductor laser device disclosed in Patent Document 1 below will be described with reference to the drawings.

  FIG. 12A shows a cross-sectional configuration of a portion including a p-side electrode in a conventional nitride semiconductor laser device, and FIG. 12B shows a planar configuration of the p-side electrode.

  As shown in FIG. 12, a conventional nitride semiconductor laser device includes an active layer and an upper portion having a ridge-shaped stripe portion and an upper portion of the ridge portion in the semiconductor laminate 1. A p-type semiconductor layer (contact layer) 2 and a p-side ohmic electrode 4 formed on the p-type semiconductor layer 2 are provided.

  The semiconductor stacked body 1 including the side surface of the stripe portion is covered with an insulating film 3, and the p-side ohmic electrode 4 includes a first thin film layer 5 made of titanium (Ti) including the upper surface and the side of the stripe portion. The pad electrode 7 is formed on the first thin film layer 5 and is formed of a second thin film layer 6 made of gold (Au) having a width smaller than that of the first thin film layer 5 and shorter than that of the stripe portion. Covered by.

  With this configuration, the pad electrode 7 can obtain good ohmic characteristics with the p-type semiconductor layer 2, and the first thin film layer 5 is provided, so that electrode peeling at the time of cleaving the semiconductor stacked body 1 hardly occurs. Become. Furthermore, by providing the second thin film layer 6, good heat dissipation can be ensured.

In Patent Document 1, the first thin film layer 5 and the second thin film layer 6 are collectively referred to as a pad electrode 7, but more strictly in the specification of the present application, the wire bonding or the heat sink. A member corresponding to the second thin film layer 6 according to Patent Document 1 used for soldering is referred to as a pad electrode, and a member corresponding to the first thin film layer 5 according to Patent Document 1 is referred to as a wiring electrode. To distinguish.
JP 2000-22272 A

  As a result of various studies on the conventional semiconductor laser device, the inventors of the present application have obtained a result that the configuration of the conventional semiconductor laser device cannot obtain sufficient reliability.

  Specifically, when a conventional semiconductor laser device is driven under a condition where the light output is constant, the operating current gradually increases with time, and at a certain point in time, the operating current rapidly increases and deteriorates irreversibly. I have confirmed the phenomenon. As a result of observing the deteriorated semiconductor laser device, it was observed that a part of the stripe portion was dissolved and destroyed in the vicinity of the end face in the stripe portion, that is, in the region where the second thin film layer 6 was not provided.

  As a result of the analysis, the phenomenon in which the operating current gradually increases with time is that the element such as Au constituting the second thin film layer 6 corresponding to the pad electrode of the present invention is the first thin film layer 5 or the p-side ohmic electrode 4. It is presumed that the non-radiative recombination centers were formed by interdiffusion and penetration into the semiconductor laminate 1. Further, an irreversible destruction near the end face that occurs at a certain time is covered with the second thin film layer 6 with respect to the central portion of the resonator covered with the second thin film layer 6 with very good heat dissipation. The temperature near the end face of the resonator that has not been increased rises relatively abnormally, and this causes a positive feedback phenomenon that lowers the band gap energy near the end face and further increases light absorption. This is presumably because the temperature rose until the electrode melted.

  In view of the above problems, the present invention is a highly reliable semiconductor that does not cause diffusion of a metal element from a pad electrode and reduces a relative temperature increase of an end surface portion with respect to a central portion of a resonator. It is an object to obtain a laser device.

  In order to achieve the above object, according to the present invention, a semiconductor laser device having a stripe-shaped current injection region is configured such that a pad electrode connected to an ohmic electrode is formed in a region outside the current injection region.

  Specifically, the semiconductor laser device includes an active layer, a semiconductor stacked body having a current injection region extending in a stripe shape above the active layer, and an ohmic electrode formed on the semiconductor stacked body so as to cover the current injection region And a pad electrode formed on the semiconductor stacked body and electrically connected to the ohmic electrode. The semiconductor stacked body includes an active layer and is formed substantially perpendicular to the longitudinal direction of the current injection region. It has a resonator having a pair of opposing cleavage planes, and the pad electrode is formed in a region excluding the upper portion of the current injection region.

  According to the semiconductor laser device of the present invention, the pad electrode formed by being electrically connected to the ohmic electrode on the semiconductor stacked body is formed in the region excluding the upper portion of the current injection region. Thus, the metal element constituting the pad electrode does not diffuse. In addition, since the pad electrode does not partially cover the current injection region that becomes high temperature during operation, the temperature generated in the portion covered with the pad electrode and the portion not covered in the current injection region (resonator) The difference becomes smaller. As a result, for example, it is possible to prevent a situation in which only the end face of the resonator is locally heated to destroy the crystallinity, thereby improving the reliability of the semiconductor laser device.

  In the semiconductor laser device of the present invention, the pad electrode is formed on the side facing the current injection region, the first region having an end reaching at least one of the pair of cleavage planes, and the current injection region for the first region It is preferable that the edge part has the 2nd area | region which is formed in the other side and is spaced apart from each cleavage surface. Thus, in the resonator in which the temperature of the end face portion is higher than that of the central portion, the end face portion portion is formed so as to reach the first region near the current injection region in the pad electrode so as to reach at least one of the cleavage planes. Since the temperature difference between the temperature of and the temperature of the central portion is further reduced, the reliability is further improved.

  In the semiconductor laser device of the present invention, it is preferable that the distance between the current injection region and the pad electrode is set smaller at both ends than the central portion of the current injection region.

  In the semiconductor laser device of the present invention, the pad electrode is preferably made of a single layer film or a laminated film containing gold or aluminum.

  In the semiconductor laser device of the present invention, the pad electrodes are preferably formed on both sides in the longitudinal direction of the current injection region on the semiconductor stacked body.

  In the semiconductor laser device of the present invention, the ohmic electrode is preferably covered with a film that enhances heat dissipation in the current injection region.

  In this case, the film is preferably made of aluminum nitride, gallium nitride, silicon oxide, aluminum oxide, silicon nitride or graphite.

  In the semiconductor laser device of the present invention, the semiconductor stacked body preferably includes a p-type semiconductor layer and an n-type semiconductor layer, and the ohmic electrode is preferably formed so as to be in contact with the p-type semiconductor layer in the semiconductor stacked body.

  In the semiconductor laser device of the present invention, the semiconductor stacked body is preferably made of a group III-V nitride semiconductor.

  According to the semiconductor laser device of the present invention, the metal element constituting the pad electrode does not diffuse into the semiconductor stacked body, and no non-radiative recombination center is formed. Furthermore, since the temperature difference between the end of the resonator and the center is reduced, the temperature rise at the end relative to the center of the resonator is suppressed, so crystal melting occurs at and near the resonator end face. As a result, the reliability of the semiconductor laser device can be greatly improved.

(First embodiment)
A first embodiment of the present invention will be described with reference to the drawings.

  1A and FIG. 1B show a nitride semiconductor laser device according to the first embodiment of the present invention, in which FIG. 1A shows a planar configuration, and FIG. 1B shows an Ib of FIG. A cross-sectional configuration taken along the line -Ib and perpendicular to the longitudinal direction of the resonator is shown.

  Here, the configuration of the nitride semiconductor laser device according to the first embodiment and the method for manufacturing the same will be described with reference to FIGS.

First, as shown in FIG. 1B, an n-type GaN layer 102 having a thickness of 3 μm and a thickness of 1 is formed on a substrate 101 made of, for example, n-type GaN by MOCVD, with a substrate temperature of 1050 ° C. An n-type cladding layer 103 made of n-type Al _0.05 Ga _0.95 N having a thickness of 2 μm and a first light guide layer 104 made of n-type GaN having a thickness of 0.08 μm are sequentially grown. Although the substrate 101 is not shown, it is in a wafer state until it is cleaved.

Subsequently, after the substrate temperature is lowered to 800 ° C., a barrier layer made of In _0.02 Ga _0.98 N having a thickness of 7.5 nm and a well layer made of In _0.10 Ga _0.90 N having a thickness of 3.0 nm are formed. A multiple quantum well (MQW) active layer 105 is formed by repeating growth for a period, and then a second light guide layer 106 made of In _0.02 Ga _0.98 N having a thickness of 50 nm is formed on the MQW active layer 105. To grow.

Next, the substrate temperature is set to 1000 ° C., the third light guide layer 107 made of GaN having a thickness of 50 nm, the p-type Al _0.20 Ga _0.80 N having a thickness of 10 nm on the second light guide layer 106. 160 p-type first cladding layer 108, a first layer made of p-type Al _0.10 Ga _0.90 N having a thickness of 1.5 nm and a second layer made of p-type GaN having a thickness of 1.5 nm for 160 periods. A p-type second cladding layer 109 having a strained superlattice structure with a thickness of 0.48 μm and a p-type contact layer 110 made of p-type GaN with a thickness of 0.05 μm are sequentially grown. By such epitaxial growth, a semiconductor stacked body 120 having a double hetero structure is formed.

Subsequently, the substrate (wafer) 101 on which the semiconductor stacked body 120 is formed is taken out of the reaction furnace, and dry etching using chlorine (Cl ₂ ) gas is performed on the contact layer 110 and the p-type second cladding layer 109. A ridge-shaped stripe portion 109a having a width of about 1.5 μm and a height of about 0.5 μm is formed. Here, the p-type contact layer 110 formed in a stripe shape becomes a current injection region in the semiconductor stacked body 120.

Next, as shown in FIG. 1A and FIG. 1B, the thickness is increased over the entire surface of the semiconductor stacked body 120 on which the stripe portion 109a is formed by a chemical vapor deposition (CVD) method. An insulating film 130 made of 0.1 μm silicon oxide (SiO ₂ ) is formed. Subsequently, the upper portion of the p-type contact layer 110 in the formed insulating film 130 is selectively removed by lithography and a dry etching method containing fluorocarbon gas as a main component to expose the p-type contact layer 110. .

  Subsequently, palladium (Pd) having a thickness of 40 nm and platinum (Pt) having a thickness of 40 nm so as to cover the upper surface and the side surface of the stripe portion 109a including the exposed p-type contact layer 110 by vacuum deposition. The p-side ohmic electrode 141 is formed in the current injection region on the upper surface of the stripe portion 109a.

  Next, the wiring electrode 142 is formed on the entire surface including the p-side ohmic electrode 141 on the insulating film 130. Thereafter, a pad electrode 143 is formed in one side region of the stripe portion 109 a on the formed wiring electrode 142. Here, the wiring electrode 142 is made of, for example, titanium (Ti) having a thickness of 50 nm and platinum (Pt) having a thickness of 100 nm from the p-side ohmic electrode 142 side by a vacuum deposition method. Further, the pad electrode 143 is formed of, for example, titanium (Ti) having a thickness of 50 nm and gold (Au) having a thickness of 1.0 μm from the wiring electrode 142 side by a vacuum deposition method or a plating method. Ti in the first layer of each of the wiring electrode 142 and the pad electrode 143 is provided in order to improve adhesion with platinum as a base metal.

  As shown in FIG. 1 (a), the planar shape of the pad electrode 143 is substantially rectangular, but a key is formed at one corner of the rectangle so that the emission end faces of the resonator end faces facing each other can be identified. The notch is provided. The dimension of the pad electrode 143 in the direction in which the stripe portion 109a extends (longitudinal direction) is 580 μm shorter than the resonator length of 600 μm, and the width in the direction perpendicular to the stripe portion 109a is 200 μm. Here, the length dimension of the pad electrode 143 is made shorter than the length dimension of the resonator, and the pad electrode 143 is formed inside the cleavage plane (resonator end face) 160 so that the pad electrode 143 is formed on a plurality of laser chips. This is for avoiding a situation in which the pad electrode 143 is peeled off or cannot be separated in the subsequent cleavage step when formed in a straddling manner. The distance d between the stripe portion 109a and the pad electrode 143 is 5 μm.

  Subsequently, the opposite surface, that is, the back surface of the n-type GaN layer 102 in the substrate 101 is polished to reduce the thickness of the substrate 101 to about 100 μm. Thereafter, the n-side ohmic electrode 150 is formed on the separated surface of the thinned substrate 101 by a vacuum deposition method or the like. Here, the n-side ohmic electrode 150 is formed by sequentially laminating titanium (Ti) having a thickness of 10 nm, platinum (Pt) having a thickness of 100 nm, and gold (Au) having a thickness of 1.0 μm from the substrate 101 side. Is formed.

  Next, the substrate 101 on which the n-side ohmic electrode 150 is formed and the semiconductor laminate 120 on which the pad electrode 143 is formed are cleaved in a direction substantially perpendicular to the longitudinal direction of the stripe portion 109a to form a bar having a width of 600 μm. The resonator end face 160 is formed by cutting. The substrate 101 cleaved in a bar shape includes a plurality of semiconductor laser devices (laser chips) in which the stripe portions 109a are positioned in parallel to each other. Subsequently, a coating film (not shown) made of a dielectric is formed on each resonator end face 160 by sputtering, for example. Here, the power reflectance with respect to the oscillation wavelength of the front end face and the rear end face is formed to be 20% and 95%, respectively.

  Next, the semiconductor laser device included in the bar-shaped substrate 101 is separated into individual laser chips by scribing.

  Thereafter, although not shown, the formed nitride semiconductor laser device is placed on a submount made of aluminum nitride (AlN) having both surfaces metallized so that the n-side ohmic electrode 150 of the substrate 101 is in contact therewith. It is fixed by a solder material made of gold tin (AuSn) by a so-called junction-up mounting method. Further, the submount to which the semiconductor laser device is fixed is fixed on a heat sink made of copper (Cu) with a solder material made of AuSn.

  Subsequently, a wire made of gold (Au) is connected to the pad electrode 143, and an electric current is applied to the connected wire and the metal electrode on the submount electrically connected to the n-side ohmic electrode 150 from the outside. By supplying, current can be injected into the stripe portion 109 a in the semiconductor stacked body 120.

  Hereinafter, the results of evaluating the operating characteristics of the nitride semiconductor laser device according to the first embodiment will be described together with a comparative example shown in FIG. As shown in FIG. 2, in this comparative example, the pad electrode 243 covers almost the entire surface of the wiring electrode 142 including the stripe portion 109a. Specifically, the longitudinal dimension of the stripe portion 109a of the pad electrode 243 is 580 μm, which is the same as that of the first embodiment, but the width in the direction perpendicular to the stripe portion 109a is 300 μm, and a part of the stripe portion 109a is a stripe. It is formed so as to cover the portion 109a. This comparative example is also mounted on a submount and a heat sink similar to the nitride semiconductor laser device according to the first embodiment, and the operation characteristics are compared.

  FIG. 3 shows representative examples of current-light output characteristics at room temperature of the semiconductor laser device according to the first embodiment and the semiconductor laser device according to the comparative example. As shown in FIG. 3, the current-light output characteristics were almost the same in both cases. However, when the number of measurements was increased and compared in more detail, the semiconductor laser device according to the first embodiment has a higher output power. It can be seen that the operating current is slightly higher. This is because, in the comparative example, the pad electrode 243 made of Au having a relatively large film thickness with excellent heat dissipation is formed immediately above the stripe portion 109a, whereas the semiconductor laser according to the first embodiment. This is because the pad electrode 143 is not provided immediately above the stripe portion 109a in the device.

  FIG. 4 shows the results of an aging test for each semiconductor laser device under the condition that the light output is a constant value of 150 mW. As can be seen from FIG. 4, the semiconductor laser device according to the comparative example has an initial operating current smaller than that of the semiconductor laser device according to the first embodiment on average, but in a relatively short time of about 500 hours. An increase in current occurs, and the operating current suddenly increases after about 1000 hours, resulting in a failure. On the other hand, the semiconductor laser device according to the first embodiment has a very small rate of increase in current, and exhibits stable operation even after 2000 hours.

  In general, it is known that the lifetime of a semiconductor laser device becomes shorter as the operating current increases, but the evaluation results shown in FIGS. 3 and 4 do not apply to this. In order to investigate this cause, the present inventor calculated the temperature distribution in the stripe direction by numerical simulation. Here, as a premise for the numerical simulation, a simple model is assumed in which heat uniformly generated in the stripe portion 109a, which is a ridge-shaped current injection region, is radiated to the heat sink through the laser chip and the submount.

  FIG. 5 shows a simulation result of the temperature distribution in the MQW active layer 105 along the stripe portion 109a during laser driving. As can be seen from FIG. 5, in the semiconductor laser device according to the first embodiment, although the temperature rises slightly in the vicinity of the end faces with distances of 0 μm and 600 μm shown on the horizontal axis, the resonator (stripe portion 109a) A relatively uniform temperature distribution is shown over the entire region.

  On the other hand, as shown in FIG. 5, the semiconductor laser device according to the comparative example reflects a good heat dissipation characteristic by the pad electrode 243, but the resonator is not covered by the pad electrode 243 although the temperature is low overall. The temperature in the vicinity of the end face 160 is greatly increased with respect to the central portion of the stripe portion 109 a covered with the pad electrode 243. As described above, in the semiconductor laser device according to the comparative example, the band gap energy of the active layer 105 is relatively small in the vicinity of the cavity end face 160 where the temperature rises locally compared to the central portion of the stripe portion 109a. Therefore, more light energy at the oscillation wavelength is absorbed. This causes a positive feedback process in which more heat is generated, and in the vicinity of the resonator end face 160, the temperature actually rises more than the numerical simulation, causing local deterioration. It is guessed.

  As described above, this local degradation is caused by heat generated during operation, and a region relatively close to the resonator end surface 160 of the pad electrode 243 diffuses into the semiconductor stacked body 120 via the p-side ohmic electrode 141. It is considered that both a mechanism for forming a non-radiative recombination center and a mechanism for melting the semiconductor stacked body 120 itself in the vicinity of the resonator end face 160 due to a temperature rise coexist.

Thus, although the semiconductor laser device according to the first embodiment has an average temperature as a laser chip higher than that of the comparative example, since the local temperature rise is small, the semiconductor stacked body 120 is hardly deteriorated. Since the nitride semiconductor is chemically extremely stable as compared with conventional gallium arsenide-based or gallium phosphide-based III-V group compound semiconductors such as AlGaAs or AlGaInP, an increase in the average temperature of the entire laser chip is a crystal. However, it is considered that the local temperature distribution has a great influence on the deterioration of crystallinity.

  As described above, according to the nitride semiconductor laser device according to the first embodiment, the pad electrode 143 having relatively excellent heat dissipation is formed away from the stripe portion 109a constituting the current injection region. Although the overall temperature rises, it is possible to prevent the temperature of the resonator end face 160 and the vicinity thereof from locally rising. Thereby, the diffusion of the metal element constituting the pad electrode 143 into the semiconductor stacked body 120 does not occur, so that a non-radiative recombination center is not formed. Furthermore, since the temperature difference between the resonator end surface 160 and the central portion of the resonator becomes small, a relative temperature increase of the end surface portion with respect to the central portion of the resonator is suppressed. As a result, crystal melting is unlikely to occur in the resonator end face 160 and the vicinity thereof, so that the reliability of the semiconductor laser device can be greatly improved.

  In the first embodiment, the dimension of the pad electrode 143 in the stripe direction is set to be 10 μm inside from the resonator end face 160, but the present invention is not limited to this. However, in consideration of the variation of the cleavage position in the cleavage step, it is desirable to take a margin of 5 μm or more from the resonator end face 160.

  Further, although the distance d between the stripe portion 109a and the pad electrode 143 is 5 μm, the present invention is not limited to this. However, if the pad electrode 143 is too close to the stripe portion 109a, a temperature difference between the central portion and the end surface portion of the stripe portion 109a is likely to occur. Therefore, it is desirable that the distance d be at least about 0.5 μm.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described with reference to the drawings.

  FIG. 6 shows a planar configuration of a nitride semiconductor laser device according to the second embodiment of the present invention. In FIG. 6, the same components as those shown in FIG. 1A are denoted by the same reference numerals, and the description thereof is omitted. The configuration of the semiconductor stacked body made of III-V nitride is also the same as that of the first embodiment.

  As shown in FIG. 6, in the semiconductor laser device according to the second embodiment, the pad electrode 143 has both ends reaching a pair of resonator end surfaces (cleavage surfaces) 160 in a region facing the stripe portion 109a. A first region 143a provided on the opposite side of the stripe portion 109a with respect to the first region 143a and an end portion shorter than the resonator length, that is, a second region provided inside the resonator end surface 160. The region 143b is configured.

  Here, the distance d between the stripe portion 109a and the first region 143a is 5 μm, and the width a of the first region 143a is 20 μm. The dimension in the longitudinal direction of the resonator in the second region 143b is set to 580 μm and the width is set to 180 μm as in the first embodiment.

  Similarly to the first embodiment, the pad electrode 143 is composed of titanium (Ti) having a thickness of 50 nm and gold (Au) having a thickness of 1.0 μm formed thereon.

  FIG. 7 shows a numerical simulation result of the temperature distribution along the stripe portion 109a in the MQW active layer 105 of the semiconductor laser device according to the second embodiment shown in FIG. For comparison, the simulation results of the semiconductor laser device according to the first embodiment shown in FIG. 1 and the semiconductor laser device according to the comparative example shown in FIG. 2 are also shown.

  As can be seen from FIG. 7, in the semiconductor laser device according to the second embodiment, the temperature rise at the resonator end face 160 is further suppressed, and a uniform temperature distribution can be realized over the entire laser chip. This is because the first region 143a close to the stripe portion 109 extends to the resonator end surface 160, and therefore the portion near the resonator end surface 160 that is most likely to generate heat in the stripe portion 109a is effectively cooled. It is.

  The inventor of the present application actually increased the operating current even after 2000 hours or more when the semiconductor laser device according to the second embodiment was continuously energized under the conditions of an optical output of 150 mW and a temperature of 70 ° C. Is not observed, and it has been confirmed that even better reliability can be obtained compared to the first embodiment.

  Here, the width a of the portion where the first region 143a is in contact with the resonator end face 160 which is a cleavage plane is 20 μm, but the present invention is not limited to this. However, the width a is preferably about 1 μm or more and less than 100 μm. This is because if the width a is less than about 1 μm, a sufficient heat dissipation effect cannot be obtained, and the temperature rise in the vicinity of the resonator end face 160 increases. On the other hand, when the width a is 100 μm or more, it is not desirable because it is difficult to cleave the pad electrode 143 with respect to the first region 143a when the semiconductor stacked body 120 is cleaved. Specifically, when the semiconductor stacked body 120 is cleaved, the pad electrode 143 is peeled off, or conversely, the pad electrode 143 is not cleaved and separated in an irregular shape such as torn, and the yield is increased. It will cause a drop.

  As described above, according to the nitride semiconductor laser device according to the second embodiment, in addition to the configuration of the semiconductor laser device according to the first embodiment, the first opposing the ridge-shaped stripe portion 109a in the pad electrode 143 is provided. Only in the region 143a, both end portions of the stripe portion 109a in the longitudinal direction extend to the resonator end surface 160, so that the temperature difference between the resonator end surface 160 and the central portion of the resonator is further reduced. Therefore, the reliability of the semiconductor laser device is further improved.

  In the second embodiment, the longitudinal dimension of the stripe portion 109a in the second region 143b of the pad electrode 143 is set to be 10 μm inside from the resonator end face, but the present invention is not limited to this. . However, in consideration of the variation of the cleavage position in the cleavage step, it is desirable to take a margin of 5 μm or more from the resonator end face 160.

  In the second embodiment, the distance d between the stripe portion 109a and the pad electrode 143 is 5 μm, but the present invention is not limited to this. However, if the pad electrode 143 is too close to the stripe portion 109a, a temperature difference between the central portion and the end surface portion of the stripe portion 109a is likely to occur.

(Third embodiment)
Hereinafter, a third embodiment of the present invention will be described with reference to the drawings.

  FIG. 8 shows a planar configuration of a nitride semiconductor laser device according to the third embodiment of the present invention. In FIG. 8, the same components as those shown in FIG. 1A are denoted by the same reference numerals, and the description thereof is omitted. The configuration of the semiconductor stacked body made of III-V nitride is also the same as that of the first embodiment.

  As shown in FIG. 8, in the semiconductor laser device according to the third embodiment, as in the second embodiment, the pad electrode 143 has a pair of resonator end faces at both ends in a region facing the stripe portion 109a. (Cleavage surface) A first region 143a provided to reach 160, and a first region 143a opposite to the stripe portion 109a with respect to the first region 143a and having an end provided inside the resonator end surface 160. 2 regions 143b.

  Here, the distance d between the stripe portion 109a and the first region 143a is 5 μm, and the width a of the first region 143a is 20 μm. The dimension in the longitudinal direction of the resonator in the second region 143b is set to 580 μm and the width is set to 180 μm as in the first embodiment.

Further, in the second embodiment, the distance between the stripe portion 109a and the first region 143a is d ₀ = 5 μm in the vicinity of the resonator end face 160, and d ₁ = in the portion excluding the vicinity of the resonator end face 160. 10 μm.

  FIG. 9 shows a numerical simulation result of the temperature distribution along the stripe portion 109a in the MQW active layer 105 of the semiconductor laser device according to the third embodiment shown in FIG. For comparison, the semiconductor laser device according to the first embodiment shown in FIG. 1, the semiconductor laser device according to the comparative example shown in FIG. 2, and the semiconductor laser device according to the second embodiment shown in FIG. The simulation results are also shown.

As can be seen from FIG. 9, in the semiconductor laser device according to the third embodiment, although the average temperature of the entire laser chip is slightly higher, the temperature in the vicinity of the resonator end face 160 and the temperature in the center of the resonator are The difference is further reduced, and a uniform temperature distribution is realized. This is because the distance between the stripe portion 109a and the pad electrode 143 is set to d ₀ at the resonator end face 160 and the vicinity thereof, and d ₁ (d ₀ <d ₁ ) is increased at other portions, thereby generating a large amount of heat. This is because heat dissipation in the vicinity of the resonator end face 160 is preferentially improved.

As described above, according to the nitride semiconductor laser device according to the third embodiment, in addition to the configuration of the semiconductor laser device according to the second embodiment, the first opposing the ridge-shaped stripe portion 109a in the pad electrode 143 is provided. The distance d ₁ between the region 143a excluding both ends and the stripe portion 109a is larger than the distance d ₀ between both ends. As a result, the temperature difference between the resonator end face 160 and the central portion of the resonator is further reduced, and the reliability of the semiconductor laser device is further improved.

In the third embodiment, the distance d ₀ between the stripe portion 109a and the pad electrode 143 is 5 μm and d ₁ is 10 μm. However, the present invention is not limited to this. The intervals d ₀ and d ₁ can be appropriately set so that the temperature difference between the central portion and the end surface portion of the stripe portion 109a is small.

  Also in the third embodiment, the width a of the portion where the first region 143a of the pad electrode 143 is in contact with the cleavage plane is 20 μm, but the present invention is not limited to this. However, about 1 μm or more and less than 100 μm is desirable for the reason shown in the second embodiment.

  In addition, although the longitudinal dimension of the stripe portion 109a in the second region 143b of the pad electrode 143 is set to be 10 μm inside from the resonator end face, it is not limited to this. However, in consideration of the variation of the cleavage position in the cleavage step, it is desirable to take a margin of 5 μm or more from the resonator end face 160.

(Fourth embodiment)
Hereinafter, a fourth embodiment of the present invention will be described with reference to the drawings.

  FIG. 10A and FIG. 10B are nitride semiconductor laser devices according to the fourth embodiment of the present invention, in which FIG. 10A shows a planar configuration, and FIG. 10B shows the Xb of FIG. A cross-sectional configuration in the direction perpendicular to the longitudinal direction of the resonator, taken along the line -Xb. 10 (a) and 10 (b), the same components as those shown in FIGS. 1 (a) and 1 (b) are denoted by the same reference numerals, and the description thereof is omitted.

  As shown in FIGS. 10A and 10B, in the fourth embodiment, the pad electrode 143 shown in the second embodiment is provided in regions on both sides of the stripe portion 109a.

  Specifically, the pad electrode 143 according to the fourth embodiment is provided so that both end portions reach a pair of resonator end surfaces (cleavage surfaces) 160 in a region facing both side surfaces of the stripe portion 109a. A first region 143a, and a second region 143b provided on the opposite side of the stripe portion 109a with respect to the first region 143a and whose end is shorter than the resonator length, that is, inside the resonator end face 160. It is constituted by.

  Here, the distance d between the stripe portion 109a and each first region 143a is 5 μm, and the width a of the first region 143a is 20 μm. The dimensions in the longitudinal direction of the resonator in each second region 143b are set to 580 μm and the width is set to 180 μm as in the first embodiment.

  Similarly to the first embodiment, the pad electrode 143 is composed of titanium (Ti) having a thickness of 50 nm and gold (Au) having a thickness of 1.0 μm formed thereon.

  Thus, according to the nitride semiconductor laser device according to the fourth embodiment, the pad electrodes 143 having the configuration of the semiconductor laser device according to the second embodiment are formed on both sides of the stripe portion 109a. Heat generated from the stripe portion 109a constituting the implantation region is more effectively dissipated. For this reason, since the average temperature of the whole stripe part 109a can be reduced, the reliability of the semiconductor laser device can be further improved.

  In the fourth embodiment, as in the second embodiment, the width a of the portion of the pad electrode 143 where the first region 143a is in contact with the cleavage plane is 20 μm in this embodiment, but the present invention is not limited to this. However, it is preferably about 1 μm or more and less than 100 μm.

  In the fourth embodiment, the longitudinal dimension of the stripe portion 109a in the second region 143b of the pad electrode 143 is set so as to be 10 μm inside from the resonator end face 160. However, the present invention is not limited to this. I can't. However, in consideration of the variation of the cleavage position in the cleavage step, it is desirable to take a margin of 5 μm or more from the resonator end face 160.

  In addition, although the interval d between the stripe portion 109a and the first region 143a of the pad electrode 143 is 5 μm, the present invention is not limited to this. However, if the pad electrode 143 is too close to the stripe portion 109a, a temperature difference between the central portion and the end surface portion of the stripe portion 109a is likely to occur.

(Fifth embodiment)
Hereinafter, a fifth embodiment of the present invention will be described with reference to the drawings.

  11A and 11B show a nitride semiconductor laser device according to the fifth embodiment of the present invention, in which FIG. 11A shows a planar configuration, and FIG. 11B shows a XIb of FIG. A cross-sectional configuration taken along the line -XIb and perpendicular to the longitudinal direction of the resonator is shown. In FIGS. 11A and 11B, the same components as those shown in FIGS. 10A and 10B are denoted by the same reference numerals, and description thereof is omitted.

  The semiconductor laser device according to the fifth embodiment includes a pad electrode 143 formed on both sides of a stripe portion 109a having the same configuration as that of the fourth embodiment, and a stripe portion 109a exposed from between the pad electrodes 143. And a heat dissipation film 170 made of, for example, aluminum nitride (AlN).

  Thus, according to the nitride semiconductor laser device according to the fifth embodiment, in addition to the configuration of the semiconductor laser device according to the fourth embodiment, heat conduction is relatively performed on the region exposed from the pad electrode 143. Since the heat dissipation film 170 having a high rate is provided, the heat generated from the stripe portion 109a can be dissipated more effectively. For this reason, since the temperature of the entire stripe portion 109a can be significantly reduced, the reliability of the semiconductor laser device can be further improved.

Note that the material constituting the heat dissipation film 170 is preferably a material that can be easily cleaved, that is, a material that is less ductile than metal. Moreover, in order to ensure favorable heat dissipation, it is desirable that the material has high thermal conductivity. Such materials include aluminum nitride (AlN), gallium nitride (GaN), silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), silicon nitride (SiN), amorphous silicon (α-Si). ) Or graphite (C), or a laminated film containing two or more of these.

  The heat dissipation film 170 made of these materials is formed by, for example, forming a resist pattern that opens a region including the stripe portion 109a on the pad electrode 143 by lithography, and then performing sputtering, vacuum deposition, or CVD. The material for forming the heat dissipation film 170 can be formed by, for example, followed by removing the resist pattern.

  In the fifth embodiment, the pad electrode 143 is provided on both sides of the stripe portion 109a as shown in the fourth embodiment. However, the present invention is not limited to this, and the first to third embodiments are not limited thereto. As described above, the same effect can be obtained in the configuration in which the pad electrode 143 is disposed only on one side of the stripe portion 109a.

  In the fifth embodiment, as in the fourth embodiment, the width a of the portion of the pad electrode 143 where the first region 143a is in contact with the cleavage plane is 20 μm in the present embodiment. However, it is preferably about 1 μm or more and less than 100 μm.

  In the fifth embodiment, the longitudinal dimension of the stripe portion 109a in the second region 143b of the pad electrode 143 is set so as to be 10 μm inside from the resonator end face 160. However, the present invention is not limited to this. I can't. However, in consideration of the variation of the cleavage position in the cleavage step, it is desirable to take a margin of 5 μm or more from the resonator end face 160.

  In addition, although the interval d between the stripe portion 109a and the first region 143a of the pad electrode 143 is 5 μm, the present invention is not limited to this. However, if the pad electrode 143 is too close to the stripe portion 109a, a temperature difference between the central portion and the end surface portion of the stripe portion 109a is likely to occur.

  Furthermore, in each of the first to fifth embodiments, gold (A) u is used as the pad electrode 143, but is not limited thereto. In the case of mounting by junction-up as in the first embodiment, any material that has excellent bonding properties with a wire may be used. For example, aluminum (Al) can be used. Further, it may be an alloy film or a laminated film containing Au or Al.

  In each embodiment, a laminated film of palladium (Pd) and platinum (Pt) is used for the p-side ohmic electrode 141. However, the present invention is not limited to this, and good ohmic characteristics can be obtained with p-type gallium nitride. Metal can be used.

  In each embodiment, the p-side ohmic electrode 141 is formed only on the upper surface and side surface of the ridge-shaped stripe portion 109a and the vicinity thereof, and is electrically connected to the pad electrode 143 through the wiring electrode 142. However, it is not always necessary to adopt such a configuration using three members. For example, instead of omitting the wiring electrode 142, the p-side ohmic electrode 141 may be formed in the same shape as the wiring electrode 142, and the pad electrode 143 may be formed directly on the p-side ohmic electrode 141.

  Moreover, in each embodiment, although the thickness of the pad electrode 143 was about 1 micrometer, it is not restricted to this. However, the thickness of the pad electrode 143 is desirably 0.3 μm or more and less than 30 μm. This is because if the thickness of the pad electrode 143 is less than 0.3 μm, wire bonding (in the case of junction-up mounting) or soldering to the heat sink (in the case of junction-down mounting) becomes difficult, and the heat dissipation also deteriorates. It is. On the other hand, when the thickness of the pad electrode 143 is 30 μm or more, the stress in the film generated at the time of vapor deposition or plating, which is a film forming process, is increased, and a defect such as peeling of the formed pad electrode 143 is likely to occur. Because it becomes.

  In each of the embodiments, the semiconductor laser device having the ridge-shaped current injection region (stripe portion 109a) above the semiconductor stacked body 120 has been described. However, the configuration is not necessarily limited thereto. For example, the same effect can be obtained even in a stripe laser device having an internal stripe portion in which a ridge-shaped stripe portion 109a is sandwiched between buried type current confinement layers.

  In each embodiment, the pad electrode 143 is electrically connected to the p-side ohmic electrode 141. However, a p-type semiconductor layer is formed on the substrate 101 side with respect to the active layer 105 of the semiconductor stacked body 120. In addition, an n-type semiconductor layer, a stripe portion, and an n-side ohmic electrode may be formed on the opposite side of the substrate 101 and electrically connected to the n-side ohmic electrode.

  Further, the semiconductor stacked body 120 is not limited to a group III-V nitride semiconductor, but can also be applied to a group III-V compound semiconductor based on gallium arsenide (GaAs) or gallium phosphide (GaP).

  The semiconductor laser device according to the present invention can greatly improve the reliability of the semiconductor laser device, and can be used for a high-density optical disk device, a laser display device, an illumination device, or the like.

(A) And (b) shows the nitride semiconductor laser device concerning the 1st Embodiment of this invention, (a) is a top view, (b) is sectional drawing in the Ib-Ib line | wire of (a). It is. It is a top view which shows the nitride semiconductor laser apparatus which concerns on a comparative example. 5 is a graph showing current-light output characteristics of the nitride semiconductor laser device according to the first embodiment of the present invention together with a comparative example. 6 is a graph showing a change in current during continuous operation of the nitride semiconductor laser device according to the first embodiment of the present invention together with a comparative example. It is the graph which showed the numerical simulation result of the temperature distribution of the stripe direction of the nitride semiconductor laser apparatus concerning the 1st Embodiment of this invention with the comparative example. It is a top view which shows the nitride semiconductor laser apparatus which concerns on the 2nd Embodiment of this invention. It is the graph which showed the numerical simulation result of the temperature distribution of the stripe direction of the nitride semiconductor laser apparatus which concerns on the 2nd Embodiment of this invention with 1st Embodiment and a comparative example. It is a top view which shows the nitride semiconductor laser apparatus which concerns on the 3rd Embodiment of this invention. It is the graph which showed the numerical simulation result of the temperature distribution of the stripe direction of the nitride semiconductor laser apparatus concerning the 3rd Embodiment of this invention with the 1st and 2nd embodiment and the comparative example. (A) And (b) shows the nitride semiconductor laser device concerning the 4th Embodiment of this invention, (a) is a top view, (b) is sectional drawing in the Xb-Xb line | wire of (a). It is. (A) And (b) shows the nitride semiconductor laser device concerning the 5th Embodiment of this invention, (a) is a top view, (b) is sectional drawing in the XIb-XIb line | wire of (a) It is. (A) And (b) shows the conventional nitride semiconductor laser apparatus, (a) is sectional drawing containing a pad electrode, (b) is a top view.

Explanation of symbols

101 Substrate 102 n-type GaN layer 103 n-type cladding layer 104 first light guide layer 105 multiple quantum well (MQW) active layer 106 second light guide layer 107 third light guide layer 108 p-type first cladding layer 109 p-type first 2 clad layer 109a stripe portion 110 p-type contact layer 120 semiconductor laminate 130 insulating film 141 p-side ohmic electrode 142 wiring electrode 143 pad electrode 143a first region 143b second region 150 n-side ohmic electrode 160 cleavage plane (resonator) End face)
170 Heat dissipation film

Claims (9)

A semiconductor laminate having an active layer and a current injection region extending in a stripe shape above the active layer;
An ohmic electrode formed on the semiconductor stack to cover the current injection region;
A pad electrode formed on the semiconductor laminate and electrically connected to the ohmic electrode;
The semiconductor laminate includes a resonator including a pair of cleavage planes that include the active layer and is formed substantially perpendicular to the longitudinal direction of the current injection region and face each other.
The semiconductor laser device according to claim 1, wherein the pad electrode is formed in a region excluding an upper portion of the current injection region.   The pad electrode is formed on a side facing the current injection region, a first region whose end reaches at least one of the pair of cleavage surfaces, and a side opposite to the current injection region with respect to the first region 2. The semiconductor laser device according to claim 1, wherein the end portion has a second region spaced apart from each of the cleavage planes.   3. The semiconductor laser device according to claim 1, wherein an interval between the current injection region and the pad electrode is set to be smaller at both ends than a central portion of the current injection region.   4. The semiconductor laser device according to claim 1, wherein the pad electrode is made of a single layer film or a laminated film containing gold or aluminum. 5.   5. The semiconductor laser device according to claim 1, wherein the pad electrode is formed on both sides in a longitudinal direction of the current injection region on the semiconductor stacked body.   The semiconductor laser device according to claim 1, wherein the ohmic electrode is covered with a film that enhances heat dissipation in the current injection region.   The semiconductor laser device according to claim 6, wherein the film is made of aluminum nitride, gallium nitride, silicon oxide, aluminum oxide, silicon nitride, amorphous silicon, or graphite. The semiconductor stacked body includes a p-type semiconductor layer and an n-type semiconductor layer,
8. The semiconductor laser device according to claim 1, wherein the ohmic electrode is formed in contact with the p-type semiconductor layer in the semiconductor stacked body. 9.   The semiconductor laser device according to claim 1, wherein the semiconductor stacked body is made of a group III-V nitride semiconductor.

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