JP2005216990A - Nitride semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor laser device which is stable in a high-power operation, suppresses the occurrence of COD (catastrophic optical damage) to prevent the deterioration of an end face, and has fine optical output characteristics. <P>SOLUTION: The nitride semiconductor laser device comprises a nitride semiconductor laser element which has a nitride semiconductor lamination consisting of a board and a plurality of nitride semiconductor layers formed on the board. The board is made of a nitride semiconductor, and the end faces of the laser element in the direction of a resonator are coated with a protective film made of an insulating material. At least one of the end faces of the laser element has current blocking areas in which no current flows, and the total length of the current blocking areas is 20% or less of the length of the resonator, or 200 μm or less. Thus, the nitride semiconductor laser element with the current blocking areas suppresses thermal or optical damage to the end face, makes the laser device stable in a high-power operation, and prevents the COD and the deterioration of the end face. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a nitride semiconductor laser device using a nitride semiconductor substrate.

  In recent years, research and development have been conducted on nitride-based semiconductor materials such as GaN as light-emitting element materials with short wavelengths such as semiconductor lasers and LEDs (light-emitting diodes). A GaN-based semiconductor laser has an InGaN active layer structure and has already been put to practical use, but currently has insufficient output for writing and rewriting of optical disk devices. Furthermore, as the speed of writing and rewriting of optical discs increases, technology for increasing the output of GaN semiconductor lasers will become more important in the future.

When increasing the output power of a semiconductor laser, degradation of the end face due to optical damage (Catastrophic Optical Damage; COD) becomes a problem. COD is a phenomenon in which oscillation stops or cannot be oscillated due to an interface state near the end face, heat generation due to light absorption, etc., resulting in an abnormally high temperature near the end face and melting of the end face. As a prior art, there has been proposed a semiconductor laser device that includes an insulating layer or a high-resistance layer between a p-side contact layer and a p-side electrode and prevents COD by forming a current non-injection region (see Patent Document 1). ). In addition, a semiconductor laser device that includes a p-side Schottky electrode that is in Schottky contact with the p-side contact layer and prevents COD by forming a current non-injection region has been proposed (see Patent Document 2).
JP 2002-43692 A JP 2003-31894 A

  Conventionally, nitride semiconductor lasers are considered to be relatively resistant to end face degradation. However, there is a concern about the occurrence of COD in a high-power laser having an output exceeding 100 mW for use in applications such as double speed and four-times speed writing of optical disks. Further, in the nitride semiconductor laser, there is a problem that the end face of the nitride semiconductor laser is deteriorated even if it is used in an air atmosphere even if it is used in an air atmosphere, even if COD does not occur. The deterioration of the end face is degradation due to oxidation and the influence of the silicon compound adhering to the end face, and when making a nitride semiconductor laser element, by taking measures such as capping or capping with nitrogen sealing, It can be prevented to some extent. However, depending on the intended use of the semiconductor laser, it may not be possible to cap it, and there is a need for a solution by improving the laser element itself.

  Conventionally, when fabricating a nitride semiconductor laser element, a sapphire substrate is usually used as a substrate on which a nitride semiconductor multilayer portion is formed. However, when compared with a nitride semiconductor substrate made of GaN or the like, the sapphire substrate has a poor thermal conductivity, with GaN being 130 W / mK and sapphire being 42 W / mK. For this reason, when manufacturing a nitride semiconductor laser device using a sapphire substrate, it is necessary to increase the width of the current non-injection region by using the technique disclosed in the above-mentioned patent document in order to suppress COD. is there. However, if the width of the current non-injection region is increased with respect to the cavity length which is the length of the laser stripe in the cavity direction, the characteristics of the nitride semiconductor laser element are deteriorated.

  FIG. 9 shows the light output-current characteristics of the nitride semiconductor laser device when the cavity length, which is the length of the laser stripe in the cavity direction, is 600 μm and the total width of the current non-injection regions is 200 μm. It is. As for the characteristics of this element, there is an abnormality such that the linearity of the graph is not clear after laser oscillation, the slope efficiency tends to decrease, and the light output is saturated even when the current value is increased. This is because the current non-injection region is wide and light absorption is large in the current non-injection region when the light output rises. Thus, if the width of the current non-injection region is increased unnecessarily in order to suppress COD, the characteristics of the nitride semiconductor laser device deteriorate. Therefore, the light output characteristics of the nitride semiconductor laser element according to the above-mentioned patent document are deteriorated.

  In view of such a problem, the present invention operates stably even at the time of high output operation, suppresses the generation of COD, does not cause end face deterioration such as end face deterioration, and at the same time, has a good light output characteristic. An object of the present invention is to propose a nitride semiconductor laser device including a semiconductor laser device.

  In order to achieve the above object, a nitride semiconductor laser device according to the present invention includes a nitride semiconductor laser element including a substrate and a nitride semiconductor stacked portion in which a plurality of nitride semiconductor layers are stacked on the surface of the substrate. And the substrate is a nitride semiconductor substrate, and a protective film made of an insulator is formed on an end surface of the nitride semiconductor laser element in the resonator direction, and at least the end surface of the nitride semiconductor laser element in the resonator direction is formed. One is provided with a current non-injection region in which no current flows, and the total length of the current non-injection region is 20% or less of the total length of the resonator, or 200 μm or less.

According to such a configuration, the use of the nitride semiconductor substrate such as GaN having higher thermal conductivity than sapphire improves the heat dissipation of the heat generated in the nitride semiconductor stacked portion. Therefore, the width of the current non-injection region can be kept small, and deterioration of the light output characteristics of the nitride semiconductor laser element can be prevented. The nitride semiconductor used for the substrate is not limited to GaN, and an Al _x Ga _1-x N substrate having a uniform Al composition in the range of 0 ≦ x ≦ 0.25 may be used. . By using the substrate, the thermal conductivity becomes even larger than when using a GaN substrate, the heat dissipation improves, and the lattice matching with the nitride semiconductor layer grown on the substrate also improves, Element characteristics are also improved.

Further, according to such a configuration, the end face is prevented from being deteriorated by forming a coating protective film on the end face. If the end face is altered, an effect such as a decrease in slope efficiency of the nitride semiconductor laser element occurs, so that the reliability of the element cannot be obtained sufficiently and it is difficult to perform a stable high output operation. The coating protective film is made of an insulating material such as ZrO ₂ , SiO ₂ , Al ₂ O ₃ , HfO ₂ , CaF, Na ₃ AlF ₆ , LiF, LaF ₃ , CeF ₃ , MgF ₂ , NdF ₃ , and AlN. It doesn't matter if it is done. The coating protective film may be made of an insulating material having an extinction coefficient of 10 ⁻⁴ or less in light having a wavelength of 400 nm.

  According to such a configuration, the total length of the current non-injection region is 20% or less of the total length of the resonator, or 200 μm or less, so that the light output characteristics of the nitride semiconductor laser device are deteriorated. Can be suppressed.

  In the nitride semiconductor laser device of the present invention, the total length of the current non-injection regions is 5 μm or more. In consideration of carrier diffusion and heat conduction from the current non-injection region to the end face, the total length of the current non-injection region is preferably 5 μm or more.

  In the nitride semiconductor laser device of the present invention, the current non-injection region is formed by providing a region without an electrode in the vicinity of an end face of a laser stripe that becomes a light emitting portion formed in the nitride semiconductor stacked portion. It is characterized by that.

  In the nitride semiconductor laser device of the present invention, the current non-injection region is formed by inserting an insulating layer between the nitride semiconductor layer and the electrode.

  In the nitride semiconductor laser device of the present invention, the current non-injection region is formed by providing a region having a high resistance in the nitride semiconductor layer.

  In the nitride semiconductor laser device of the present invention, the current non-injection region is formed by making a Schottky contact between the nitride semiconductor layer and the electrode.

  According to the present invention, a nitride semiconductor substrate with good heat dissipation is used, a protective layer made of an insulator is formed on the end face, and a current non-injection region is formed on at least one of the end faces of the waveguide. It is possible to realize a nitride semiconductor laser device that suppresses thermal and optical damage, operates stably even at high output operation, does not cause COD, and does not cause end face deterioration such as end face deterioration.

<First Embodiment>
A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a structure of a nitride semiconductor growth layer stacked on a nitride semiconductor substrate in the present embodiment.

As shown in FIG. 1, the nitride semiconductor growth layer 116 is formed on the surface of a nitride semiconductor substrate 101 made of n-type GaN, on an n-type GaN layer 102 having a layer thickness of 3 μm, and an n-type having a layer thickness of 0.5 μm. Al _0.1 Ga _0.9 N cladding layer 103, n-type GaN optical guide layer 104 with a thickness of 0.1 μm, 4 In _0.01 Ga _0.99 N barrier layers with a thickness of 8 nm and an In _0.1 Ga _0.9 N well with a thickness of 4 nm The multi-quantum well structure light-emitting layer 105 having three layers, a p-type Al _0.3 Ga _0.7 N carrier blocking layer 106 having a layer thickness of 20 nm, a p-type GaN light guide layer 107 having a layer thickness of 0.1 μm, and a layer thickness of 0 A .4 μm p-type Al _0.1 Ga _0.9 N clad layer 108 and a p-type GaN contact layer 109 having a layer thickness of 0.1 μm are sequentially stacked. In the present invention, an n-type GaN substrate is used as the material of the nitride semiconductor substrate 101 as the nitride semiconductor substrate. However, the material is not limited to this material. A GaN substrate, an Al _1-x Ga _x N (0 ≦ x ≦ 1) substrate, or the like may be used.

  Next, a method for manufacturing the above-described nitride semiconductor growth layer 116 will be described. In the following description, the case where the MOCVD method (Metal Organic Chemical Vapor Deposition) is used is shown. However, the growth method is not limited to the MOCVD method as long as it is an epitaxial growth method. Other vapor phase growth methods such as a molecular beam epitaxy method and a HDVPE method (Hydride Vapor Phase Epitaxy) may be used.

The nitride semiconductor substrate 101 is placed on a predetermined susceptor in the growth furnace of the MOCVD apparatus, and the susceptor temperature is raised to 1050 ° C. while flowing N ₂ and NH ₃ as carrier gases at a rate of 5 l / min. When the temperature rise is completed, the carrier gas is changed from N ₂ to H _2, and trimethylgallium ((CH ₃ ) ₃ Ga: TMG) as a raw material for Ga is 100 μmol / min, and SiH ₄ is 10 nmol / min in the growth reactor. Then, the n-type GaN layer 102 is grown by 3 μm. Thereafter, TMG is reduced to 50 μmol / min, and 40 μmol / min of trimethylaluminum ((CH ₃ ) ₃ Al: TMA) as an Al raw material is supplied into the growth reactor, and the n-type Al _0.1 Ga _0.9 N cladding layer 103 is supplied. Is grown to 0.5 μm. When the growth of the n-type Al _0.1 Ga _0.9 N cladding layer 103 is completed, the supply of TMA is stopped, the TMG is increased to 100 μmol / min, and the n-type GaN light guide layer 104 is grown to 0.1 μm. Thereafter, the supply of TMG and SiH ₄ is stopped, the carrier gas is changed from H ₂ to N ₂ , the susceptor temperature is lowered to 700 ° C., and trimethylindium ((CH ₃ ) ₃ In: TMI) is used as the indium raw material. 10 μmol / min and TMG 15 μmol / min are supplied into the growth furnace to grow an 8 nm-thick barrier layer made of In _0.01 Ga _0.99 N. Next, the TMI supply amount is increased to 50 μmol / min, and a 4 nm thick well layer made of In _0.1 Ga _0.9 N is grown. In the same manner, a total of three well layers are grown to form a multiple quantum well light-emitting layer 105 composed of a total of four barrier layers between and on both sides of the well layer.

When the multi-quantum well light-emitting layer 105 is formed, the supply of TMI and TMG is stopped, the susceptor temperature is increased to 1050 ° C., the carrier gas is changed from N ₂ to H ₂ , and TMG is 50 μmol / min, TMA is supplied at 30 μmol / min, and bisethylcyclopentadienylmagnesium ((C ₂ H ₅ C ₅ H ₄ ) ₂ Mg: EtCp ₂ Mg) is supplied into the growth reactor as a raw material for Mg which is a p-type dopant. The p-type Al _0.3 Ga _0.7 N carrier blocking layer 106 is grown to 20 nm. When the growth of the p-type Al _0.3 Ga _0.7 N carrier block layer 106 is completed, the supply of TMA is stopped, the supply amount of TMG is increased to 100 μmol / min, and the p-type GaN light guide layer 107 is grown by 0.1 μm. Subsequently, the supply of TMG is reduced to 50 μmol / min, TMA is supplied into the growth furnace at 40 μmol / min, the p-type Al _0.1 Ga _0.9 N cladding layer 108 is grown to 0.4 μm, and then the supply of TMG is performed. The TMA supply is stopped, the p-type GaN contact layer 109 is grown by 0.1 μm, and the growth of the semiconductor laminated film of the nitride semiconductor laser device is completed. Thereafter, the supply of TMG and EtCp ₂ Mg is stopped and the temperature is lowered. In this manner, the nitride semiconductor substrate 101 (wafer) having the nitride semiconductor growth layer 116 formed on the surface is obtained.

  After the nitride semiconductor growth layer 116 is formed on the nitride semiconductor substrate 101 as described above, a nitride semiconductor laser device is manufactured. Hereinafter, a method for manufacturing a nitride semiconductor laser device will be described with reference to the drawings. FIG. 2 is a schematic configuration diagram showing a multilayer structure of the nitride semiconductor laser device according to this embodiment. FIG. 3 is a top view of the wafer on which the nitride semiconductor laser device according to this embodiment is formed as viewed from the p-type electrode side. is there.

First, the p-type Al _0.1 Ga _0.9 N clad layer 108 and the p-type GaN contact layer 109 are etched so as to form a ridge stripe structure having a width of about 2 μm by using a normal photolithography technique and a dry etching technique. A portion of the p-type Al _0.1 Ga _0.9 N cladding layer 108 is etched to form a ridge stripe 120 having a striped ridge structure extending in the resonator direction, and then a nitride semiconductor growth layer excluding the upper portion of the ridge stripe 120 An SiO ₂ buried layer 110 is formed on the surface of 116 as an insulating layer for current confinement. Next, as shown in FIG. 2, after sequentially depositing palladium (Pd), molybdenum (Mo), and gold (Au), the electrode is heated at a high temperature so as to obtain ohmic contact with the p-type GaN contact layer 109. Alloying is performed to form the p-type electrode 111. Next, a p-type electrode region 300 as shown in FIG. 3 is formed using a normal photolithography technique and a dry etching technique. At this time, as shown in FIG. 3, the p-type electrode length Y which is the length of the p-type electrode in the resonator direction is made shorter than the resonator length X which is the length of the ridge stripe in the resonator direction. A region where no p-type electrode is formed is formed on the ridge stripe 120. This region becomes the current non-injection region 304. In this embodiment, the resonator length X is 600 μm, and the p-type electrode length Y is 500 μm.

  Next, the wafer on which the nitride semiconductor laser element is formed as described above is divided into bars. At this time, as shown in FIG. 3, a region where a p-type electrode provided between p-type electrode regions 300 adjacent in a direction along the ridge stripe 120 (hereinafter referred to as “stripe direction”) is not formed. A bar dividing line 302 is formed on the substrate, and division (cleavage) is performed along the bar dividing line 302 extending in a direction perpendicular to the stripe direction. When divided in this way, a bar 303 is formed in which a nitride semiconductor laser element having a 50 μm region from both ends of the ridge stripe 120 as a current non-injection region 304 is formed. The method for forming the current non-injection region is not limited to the above-described method, and the p-type electrode 111 is formed on the entire surface of the ridge stripe 120 and divided into bars 303, and then a technique such as dry etching or wet etching is used. Alternatively, a method of removing the p-type electrode 111 only at the end face portion and forming a current non-injection region may be used.

  In this embodiment, the width Z in the stripe direction of the current non-injection region 304 is 100 μm, but is not limited to this, and the current non-injection region is within a range not exceeding 20% of the resonator length X. A width Z of 304 can be set. If the width Z of the current non-injection region 304 is larger than 20% of the resonator length X, the light output-current characteristics of the nitride semiconductor laser element are adversely affected. For this reason, the width Z of the current non-injection region 304 is preferably within 20% of the resonator length X. In the present embodiment, the current non-injection regions 304 are provided on both sides of the end face of the bar 303. However, the present invention is not limited to this, and the current non-injection area 304 may be formed only on one side of the end face. In consideration of carrier diffusion and heat conduction from the current non-injection region to the end face, the total length of the current non-injection region is preferably 5 μm or more.

  After the current non-injection region 304 is formed as described above, cleavage is performed along the bar dividing line 302. To facilitate this cleavage, the back surface of the nitride semiconductor substrate 101 is ground or polished. . Then, an n-type electrode 112 made of hafnium (Hf) and aluminum (Al) is formed on the back surface of the nitride semiconductor substrate 101 that has been ground or polished, and the nitride semiconductor substrate 101 is made of n-type GaN. The electrode is alloyed at a high temperature so that an ohmic contact can be obtained. Subsequently, an n-type metal layer 113 made of molybdenum (Mo), platinum (Pt), and gold (Au) is formed on the surface of the n-type electrode 112.

As described above, the wafer formed in this way is cleaved along the bar dividing line 302 as described above to divide the wafer into bars 303 having a resonator length X in the resonator direction of 600 μm. A coating protective film 114 is formed of an insulator on both front and rear end faces of the divided bar 303. The coating protective film 114 is made of an insulating material having an extinction coefficient of 10 ⁻⁴ or less in light having a wavelength of 400 nm, so that the reflectance at the resonator end face by the coating protective film 114 is optimized. Can be controlled. Examples of the material for the coating protective film 114 include ZrO ₂ , SiO ₂ , Al ₂ O ₃ , HfO ₂ , CaF, Na ₃ AlF ₆ , LiF, LaF ₃ , CeF ₃ , MgF ₂ , NdF ₃ , and AlN. May be used. The end face coating may be formed not only for controlling the reflectance but also for protecting the end face.

  In addition, the end face can be prevented from being deteriorated by coating the end face, and the characteristics of other nitride semiconductor laser elements such as a threshold value and slope efficiency can be improved.

  Further, the nitride semiconductor laser elements are divided one by one from the bar 303 in the bar state. A nitride semiconductor laser device is obtained by mounting the nitride semiconductor laser element thus formed on a heat sink. The current-light output characteristics of the nitride semiconductor laser device thus fabricated were evaluated. There was no kink up to an optical output of 180 mW, and no COD was generated. The width of one side of the current non-injection region 304 of the nitride semiconductor laser element is 50 μm.

  Next, a nitride semiconductor laser device was manufactured by changing the resonator length X, and the optical output-current characteristics were evaluated. If the total length of the current non-injection region 304 in the resonator direction is 20% or less of the resonator length X, the light output saturation as shown in FIG. 9 does not occur, and even in a high output operation up to an optical output of 180 mW. COD does not occur.

  Further, when the nitride semiconductor laser element is mounted on the heat sink, if the p-type electrode 111 side is mounted by the junction down method in which the heat sink is mounted on the heat sink, the heat generated by laser oscillation is more efficiently dissipated to the heat sink. . As a result, the generation of COD is further suppressed.

<Second Embodiment>
A second embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a schematic configuration diagram showing a multilayer structure of the nitride semiconductor laser device according to the present embodiment. Note that the configuration and the manufacturing method of the nitride semiconductor growth layer 116 stacked on the nitride semiconductor substrate 101 in this embodiment are the same as those in the first embodiment, and the detailed description thereof will be described in the first embodiment. It is omitted as referring to the form.

  After the nitride semiconductor growth layer 116 is formed on the nitride semiconductor substrate 101 as shown in FIG. 1 as in the first embodiment, a nitride semiconductor laser device is manufactured. Hereinafter, a method for manufacturing a nitride semiconductor laser device will be described with reference to the drawings.

  First, a ridge stripe pattern having a width of about 2 μm is formed using a photolithography technique. In this photolithography process, a positive photoresist is used in which a portion exposed to light for exposure is removed in a later development process. In this case, the photomask usually has a light-shielding property with a stripe pattern portion made of a material such as Cr (chromium), and the other portions are light-transmitting. On the other hand, in this embodiment, a part of the stripe pattern of the photomask is made of a material that partially transmits light, such as an optical filter. As a result, the exposure time is adjusted, and a part of the resist in the stripe pattern is in a half-exposure state. Therefore, when immersed in the developer, the resist film thickness of the stripe pattern in the light-shielded portion does not change, but the resist film thickness of the stripe pattern in the semi-exposed state becomes thin.

Thus, the ridge stripe 520 is formed by the RIE (Reactive Ion Etching) technique using a reactive gas such as chlorine (Cl ₂ ) using the photoresist pattern formed on the surface of the nitride semiconductor growth layer 116. The etching depth by RIE is about 0.6 μm in the portion where the exposure is performed and the resist pattern is not formed, and the vicinity of the interface between the p-type GaN light guide layer 107 and the p-type Al _0.3 Ga _0.7 N carrier block layer 106 Etching was performed until. On the other hand, in the portion where the resist film thickness is thinner than usual on the ridge stripe 520, the resist is completely removed by RIE, and the nitride semiconductor growth layer 116 directly under the resist is etched by about several hundred nm. In this way, by changing the etching amount of the nitride semiconductor growth layer 116 depending on the position of the stripe pattern, the ridge stripe 520 having a step is formed. In this embodiment, the stepped ridge stripe 520 is formed by a method using one photomask. However, the present invention is not limited to this method. For example, two photomasks having different patterns are used. The ridge stripe 520 may be formed by a method such as changing the etching depth by RIE for the resist pattern formed by each photomask.

Next, an SiO ₂ buried layer 110 is formed as an insulating layer for current confinement to a thickness of 250 nm on the surface of the nitride semiconductor growth layer 116 after etching, and subsequently, the SiO ₂ on the ridge stripe 520 is peeled off together with the resist. At this time, the SiO ₂ insulating layer 510 formed on the upper step portion of the step portion on the ridge stripe 520 is not removed. Subsequently, a p-type electrode 111 made of palladium (Pd), molybdenum (Mo), and gold (Au) is deposited, and the electrode is alloyed at a high temperature. In this way, the SiO ₂ insulating layer 510 is inserted in the upper part of the step portion formed in the ridge stripe 520 between the p-type electrode 111 constituting the ridge stripe 520 and the p-type GaN contact layer 109, and this portion becomes the current. A structure to be a non-implanted region is formed.

  Further, the nitride semiconductor substrate 101 was ground and polished from the back surface so that cleavage can be easily performed. An n-type electrode 112 made of hafnium (Hf) or titanium (Ti) is formed on the back surface of the nitride semiconductor substrate 101, and the electrodes are alloyed at a high temperature. Subsequently, an n-type metal layer 113 made of molybdenum (Mo), platinum (Pt), and gold (Au) is formed on the n-type electrode 112.

The wafer thus formed was divided into bars using a scribe device with a resonator length of 600 μm. A coating protective film 114 is formed of an insulator on both front and rear end faces of the divided bar. The coating protective film 114 is made of an insulating material having an extinction coefficient of 10 ⁻⁴ or less in light having a wavelength of 400 nm, so that the reflectance at the resonator end face by the coating protective film 114 is optimized. Can be controlled. Examples of the material for the coating protective film 114 include ZrO ₂ , SiO ₂ , Al ₂ O ₃ , HfO ₂ , CaF, Na ₃ AlF ₆ , LiF, LaF ₃ , CeF ₃ , MgF ₂ , NdF ₃ , and AlN. May be used. The end face coating may be formed not only for controlling the reflectance but also for protecting the end face. Next, the nitride semiconductor laser elements were divided into one from the bar state. The nitride semiconductor laser element formed in this way is mounted on a heat sink to obtain a semiconductor laser device.

In the present embodiment, as described above, the SiO ₂ insulating layer 510 is inserted under the p-type electrode 111 to form the current non-injection regions. However, the current non-injection regions are formed on the ridge stripe 520 at intervals of 600 μm. The width of the current non-injection region in which SiO ₂ is inserted below the p-type electrode 111 is 100 μm. In addition, when the wafer is divided into bars, cleavage is performed at the center of the current non-injection region so that regions having a width of 50 μm from both sides of the laser resonator end face become current non-injection regions.

The nitride semiconductor laser device manufactured as described above did not generate kinks and did not generate COD up to an optical output of 180 mW. On the other hand, the width of the current non-injection region formed by inserting the SiO ₂ insulating layer 510 under the p-type electrode 111 is set to 200 μm, the bar is divided at the center, and the region having a width of 100 μm from both sides of the resonator end face A nitride semiconductor laser device was fabricated so as to be a non-injection region. When the current-light output characteristics of the nitride semiconductor laser device were evaluated, the light output was saturated at about 30 mW. The reason for the saturation of the light output is that the current non-injection region is wide and light absorption is large in the current non-injection region when the light output rises.

Further, a nitride semiconductor laser device in which a SiO ₂ insulating layer 510 was inserted under the ridge stripe of the p-type electrode 111 to form a current non-injection region by changing the resonator length was produced. When the total length in the resonator direction was 20% or less of the resonator length, saturation of the optical output did not occur, and COD did not occur even at high output operation up to 200 mW.

<Third Embodiment>
A third embodiment of the present invention will be described with reference to the drawings. FIG. 5 is a schematic configuration diagram showing a multilayer structure of the nitride semiconductor laser device according to this embodiment. Note that the configuration and the manufacturing method of the nitride semiconductor growth layer 116 stacked on the nitride semiconductor substrate 101 in this embodiment are the same as those in the first embodiment, and the detailed description thereof will be described in the first embodiment. It is omitted as referring to the form.

  As in the first embodiment, a resist mask is formed in a partial region on the wafer surface where the nitride semiconductor growth layer 116 shown in FIG. 1 is formed on the nitride semiconductor substrate 101 by using a photolithography technique. . Next, ion implantation into the nitride semiconductor growth layer 116 is performed on the wafer using an ion implanter or the like. In this embodiment, boron (B) is used for ions to be implanted, but the ion species is not limited to this, and argon (Ar), xenon (Xe), krypton (Kr), or the like may be used. Further, the depth of penetration of the implanted ions is such that it reaches the p-type GaN contact layer 109 of the nitride semiconductor growth layer 116 and damages the multi-quantum well structure light emitting layer 105 in the nitride semiconductor growth layer 116. The ion energy to be implanted is set so as not to be given. Incidentally, in the portion covered with the resist, the ions are blocked by the resist and do not enter the nitride semiconductor growth layer 116. In the region where ions are implanted, a defect occurs due to the crystal state of the p-type GaN contact layer 109 being broken, and the p-type GaN contact layer 109 is damaged. As a result, a high resistance region 610 is formed.

In this embodiment, ion implantation is performed using an ion implanter, but the ion implantation method is not limited to this, and for example, a method such as plasma doping using a dry etching apparatus is used. You may use. In this embodiment, the high resistance region 610 is formed on the surface of the p-type GaN contact layer 109. However, if the multi-quantum well structure light-emitting layer 105 is not damaged, the stacked p-type Al _0.3 Ga is used. _Even if the high resistance region 610 is formed in any one of the _0.7 N carrier block layer 106, the p-type GaN light guide layer 107, the p-type Al _0.1 Ga _0.9 N cladding layer 108, and the p-type GaN contact layer 109. I do not care.

When the ion implantation is completed, the resist is peeled off. Next, the ridge stripe 620 is formed by using a photolithography technique and a dry etching technique. As shown in FIG. 6, the ridge stripe 620 is formed in a direction perpendicular to the high resistance region 610. The ridge stripe 620 is formed by forming a ridge stripe pattern having a width of 2 μm using a resist on a wafer by using a photolithography technique and removing the other portions by dry etching. Next, after forming the SiO ₂ buried layer 110 as an insulating layer for current confinement, the SiO ₂ on the ridge stripe 620 is removed. Subsequently, a p-type electrode 111 made of Pd, Mo, and Au is formed, and the electrode is alloyed at a high temperature.

Further, after grinding and polishing from the back surface side of the nitride semiconductor substrate 101, an n-type electrode 112 made of Hf and Al is formed on the back surface side of the nitride semiconductor substrate 101. Next, after the n-type electrode is alloyed, an n-type metal layer 113 made of Mo, Pt, and Au is formed on the surface of the n-type electrode 112. Next, the wafer is divided into bars along a bar dividing line 302, and a coating protective film 114 is formed of an insulator on both front and rear end faces of the divided bars. The coating protective film 114 is made of an insulating material having an extinction coefficient of 10 ⁻⁴ or less in light having a wavelength of 400 nm, so that the reflectance at the resonator end face by the coating protective film 114 is optimized. Can be controlled. Examples of the material for the coating protective film 114 include ZrO ₂ , SiO ₂ , Al ₂ O ₃ , HfO ₂ , CaF, Na ₃ AlF ₆ , LiF, LaF ₃ , CeF ₃ , MgF ₂ , NdF ₃ , and AlN. May be used. The end face coating may be formed not only for controlling the reflectance but also for protecting the end face. Next, the nitride semiconductor laser element is divided from the bar state. When the division is completed, the nitride semiconductor laser device is mounted on a heat sink and wiring, a cap, and the like are attached, and a nitride semiconductor laser device is obtained.

  In this embodiment, as shown in FIG. 6, the high resistance regions 610 are provided at a pitch of 600 μm in the direction perpendicular to the ridge stripe 620 direction, and the width W of the high resistance region 610 is 100 μm. When the bar division is performed, the division is performed along the bar division line 302 at the center of the high resistance region 610, and a region having a width of 50 μm from both ends of the formed resonator end face becomes the high resistance region 610. The stripe portion of the high resistance region 610 becomes a current non-injection region 702.

  When the current-light output characteristics of the nitride semiconductor laser device formed by the above-described method were evaluated, end face destruction due to COD did not occur even when the light output exceeded 180 mW. When the nitride semiconductor laser device manufactured so that the width of the current non-injection region 702 is about 100 μm on one side from the end face was evaluated, the light output was saturated at about 30 mW. This is because the current non-injection region is too wide and light absorption in this region is increased.

<Fourth Embodiment>
A fourth embodiment of the present invention will be described with reference to the drawings. FIG. 7 is a schematic configuration diagram showing a multilayer structure of the nitride semiconductor laser device according to the present embodiment. Note that the configuration and the manufacturing method of the nitride semiconductor growth layer 116 stacked on the nitride semiconductor substrate 101 in this embodiment are the same as those in the first embodiment, and the detailed description thereof will be described in the first embodiment. It is omitted as referring to the form.

  As in the first embodiment, a resist mask is formed in a partial region on the wafer surface where the nitride semiconductor growth layer 116 shown in FIG. 1 is formed on the nitride semiconductor substrate 101 by using a photolithography technique. . Next, the surface layer of the exposed portion of the nitride semiconductor growth layer 116 not covered with the resist mask is damaged. However, damage should be prevented from occurring in the region covered with the resist mask. In the present embodiment, by using the RIE technique and etching the outermost surface of the portion where the semiconductor growth layer is exposed, the crystal state of the surface layer is destroyed and a defect is generated, or in the reactive gas used for the etching Damage regions 810 are formed by damaging the surface layer by implanting ions or the like as impurities. Note that the method of damaging the surface layer is not limited to RIE, and a method such as irradiation with a laser or an electron beam may be used. Further, the etching amount of the surface layer is not limited.

  The etched portion of the surface layer is damaged, and an electrode is formed on the surface. Even if the electrode is alloyed at a high temperature, the semiconductor layer and the electrode cannot obtain ohmic contact, and the Schottky barrier is not formed. Formed and no current flows. As a result, the damaged region of the surface layer becomes a current non-injection region. When the surface layer is mildly damaged, a current flows when a voltage is applied to the nitride semiconductor laser element having a current non-injection region at a certain value or more. Therefore, it is preferable to damage the surface layer so as to maintain the Schottky barrier with a driving voltage that is highly likely to generate COD.

After damaging the surface layer, the resist is peeled off. Subsequently, a ridge stripe 820 is formed. The ridge stripe 820 is formed in a direction perpendicular to the damage region 810. As a method for forming the ridge stripe 820, a ridge stripe pattern made of a resist having a width of 2 μm is formed on a wafer by a photolithography technique. The other portions are removed by the RIE technique to form a ridge stripe 820. Further, after the SiO ₂ buried layer 110 is formed as an insulating film for current confinement, the SiO ₂ on the ridge stripe 820 is removed. Subsequently, a p-type electrode 111 made of Pd, Mo, and Au is formed, and the electrode is alloyed at a high temperature. At this time, in the region where the surface layer is not damaged, the p-type electrode 111 and the p-type GaN contact layer 109 are in ohmic contact, but in the damaged region 810 which is a region where the surface layer is damaged, the Schottky A contact is formed, resulting in a current non-injection region where no current flows.

Next, after grinding and polishing from the back surface side of the nitride semiconductor substrate 101, an n-type electrode 112 made of Hf and Al is formed on the back surface side of the nitride semiconductor substrate 101. After alloying the n-type electrode 112 at a high temperature, an n-type metal layer 113 made of Mo, Pt, and Au is formed on the surface of the n-type electrode 112 in this order from the nitride semiconductor substrate 101 side. The wafer thus manufactured is divided into bars along a bar dividing line 302. A coating protective film 114 is formed of an insulator on both front and rear end faces of the divided bar 903 (see FIG. 8). The coating protective film 114 is made of an insulating material having an extinction coefficient of 10 ⁻⁴ or less in light having a wavelength of 400 nm, so that the reflectance at the resonator end face by the coating protective film 114 is optimized. Can be controlled. Examples of the material for the coating protective film 114 include ZrO ₂ , SiO ₂ , Al ₂ O ₃ , HfO ₂ , CaF, Na ₃ AlF ₆ , LiF, LaF ₃ , CeF ₃ , MgF ₂ , NdF ₃ , and AlN. May be used. The end face coating may be formed not only for controlling the reflectance but also for protecting the end face. Next, the bar 903 is divided into nitride semiconductor laser elements. Next, the divided nitride semiconductor laser element is mounted on a heat sink, and wiring, a cap, etc. are attached, and a semiconductor laser device is obtained.

  Further, in this embodiment, as shown in FIG. 8, the damaged regions 810 are provided at a pitch of 600 μm perpendicular to the ridge stripe direction, and the width thereof is 100 μm. In the case of dividing into nitride semiconductor laser elements, division is performed along the bar dividing line 302 at the center of the damaged region 810, and an area having a width of 50 μm from both ends of the end face in the resonator direction of the divided nitride semiconductor laser element. Becomes the damage region 810. The stripe portion 902 of the damaged region 810 forms a Schottky contact as described above and is a current non-injection region.

  When the current-light output characteristics of the nitride semiconductor laser device fabricated by the above-described method were evaluated, even when the light output exceeded 180 mW, end face destruction due to COD did not occur. On the other hand, when the width of the damaged region 810 was 100 μm on one side and the total was 200 μm, the light output was saturated at about 30 mW. This is because light absorption in this portion is increased because the current non-injection region is wide. As in the other embodiments, the width of the damaged region 810 that is in Schottky contact is preferably 20% or less of the resonator length X.

It is a schematic block diagram which shows the structure of the nitride semiconductor growth layer laminated | stacked on the nitride semiconductor substrate in embodiment of this invention. 1 is a schematic configuration diagram showing a multilayer structure of a nitride semiconductor laser device according to a first embodiment of the present invention. 1 is a top view of a wafer on which a nitride semiconductor laser device according to a first embodiment of the present invention is formed as viewed from a p-type electrode side. It is a schematic block diagram which shows the multilayer structure of the nitride semiconductor laser element in the 2nd Embodiment of this invention. It is a schematic block diagram which shows the multilayer structure of the nitride semiconductor laser element in the 3rd Embodiment of this invention. It is the top view which looked at the wafer in which the nitride semiconductor laser element in the 3rd Embodiment of this invention was formed from the p-type electrode side. It is a schematic block diagram which shows the multilayer structure of the nitride semiconductor laser element in the 4th Embodiment of this invention. It is the top view which looked at the wafer in which the nitride semiconductor laser element in the 4th Embodiment of this invention was formed from the p-type electrode side. It is a figure which shows the optical output-current characteristic of the nitride semiconductor laser element.

Explanation of symbols

Reference Signs List 101 Nitride semiconductor substrate 102 n-type GaN layer 103 n-type Al _0.1 Ga _0.9 N cladding layer 104 n-type GaN light guide layer 105 multiple quantum well structure light-emitting layer 106 p-type Al _0.3 Ga _0.7 N carrier block layer 107 p-type GaN light Guide layer 108 p-type Al _0.1 Ga _0.9 N cladding layer 109 p-type GaN contact layer 110 SiO ₂ buried layer 111 p-type electrode 112 n-type electrode 113 n-type metal layer 114 coating protective film 116 nitride semiconductor growth layer 120 ridge stripe 300 p-type electrode region 302 bar dividing line 303 bar 304 current non-injection region 510 SiO ₂ insulating layer 520 ridge stripe 610 high resistance region 620 ridge stripe 702 current non-injection region 703 bar 810 damage region 820 ridge stripe 902 Flow non-injection area 903 bar

Claims (6)

In a nitride semiconductor laser device including a substrate and a nitride semiconductor stacked portion in which a plurality of nitride semiconductor layers are stacked on the surface of the substrate,
The substrate is a nitride semiconductor substrate;
A protective film made of an insulator is formed on the end face of the nitride semiconductor laser element in the cavity direction,
At least one of the end faces in the cavity direction of the nitride semiconductor laser element includes a current non-injection region where no current flows,
The total length of the current non-injection region is 20% or less of the total length of the resonator, or 200 μm or less.   The nitride semiconductor laser device according to claim 1, wherein the total length of the current non-injection regions is 5 μm or more.   3. The current non-injection region is formed by providing a region without an electrode in the vicinity of an end face of a laser stripe that becomes a light emitting portion formed in the nitride semiconductor multilayer portion. The nitride semiconductor laser device described in 1.   3. The nitride semiconductor laser device according to claim 1, wherein the current non-injection region is formed by inserting an insulating layer between the nitride semiconductor layer and the electrode.   3. The nitride semiconductor laser device according to claim 1, wherein the current non-injection region is formed by providing a region having a high resistance in the nitride semiconductor layer. 4.   3. The nitride semiconductor laser device according to claim 1, wherein the current non-injection region is formed by making a Schottky contact between the nitride semiconductor layer and the electrode. 4.

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