JP2011029224A - Semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a nitride semiconductor laser device that facilitates cleavage and suppresses a minute leakage current. <P>SOLUTION: The semiconductor laser device includes a semiconductor layer laminate 100 including an n-type cladding layer 103, an active layer 105 and a p-type cladding layer 108 which are sequentially laminated on a substrate 101, and forming a resonator. The semiconductor layer laminate 100 has: a ridge 110 extending like a stripe between a front edge 108 emitting light and a rear edge 109 opposite to the front edge 108; first grooves 112 formed on both sides of the ridge 110; a pedestal 113 separated from the ridge 110 by the first grooves 112; and second grooves 114 formed respectively on regions including the front edge 108 and the rear edge 109 in the pedestal 113, and separated from the first grooves 112. The second grooves 114 are deeper than the first grooves 112. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a semiconductor laser device, and more particularly to a blue to ultraviolet semiconductor laser device using a nitride semiconductor.

Group III-V compound semiconductor laser devices such as AlGaAs infrared laser devices or InGaP red laser devices are widely used as elements for communication devices or elements for reading and writing for CDs or DVDs. In recent years, by using a nitride semiconductor having a general formula of Al _x Ga _y In _(1-xy) N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1), Short blue and ultraviolet semiconductor laser devices have been realized. A semiconductor laser device using a nitride semiconductor has been put into practical use as a writing and reading light source for a high-density optical disk such as a next-generation DVD using blue laser light. Currently, a blue laser device of 200 mW is commercially available, but in the future, further increase in output is required to improve the recording speed, and a 300 mW class laser device is expected to appear on the market soon.

  In general, in a semiconductor laser device, a cavity end face is formed by cleavage. Infrared and red semiconductor laser devices formed of zincblende structure semiconductor materials such as AlGaInAs and AlGaInP are highly cleaved because the cleavage plane is every 90 degrees. However, since nitride semiconductors such as GaN have a hexagonal wurtzite structure, a plane shifted by 60 degrees from the (1-100) plane which is a cleavage plane is also an equivalent cleavage plane. For this reason, at the time of cleavage, cracks also occur in the direction of 60 degrees with respect to the cleavage direction, and it is difficult to form a structurally stable cleavage plane.

  In order to solve this problem, a method of cleaving by breaking using a scribe flaw formed in a broken line shape using a diamond needle or the like in a nitride semiconductor layer as a cleavage guide has been studied (for example, Patent Document 1). reference.). In addition, a method of forming a cleavage guide groove by etching has been studied (for example, see Patent Documents 2 to 3). However, in the case of the nitride semiconductor material, since the cleavage property is essentially low and the cleavage surface is also in the direction of 60 degrees, even if the cleavage guide groove is formed, cleavage does not occur along the groove, There is a risk of cleaving from other than the tip of the groove. The inventors of the present application have found that the groove depth and shape need to be optimized in order to control the cleavage more accurately (see, for example, Patent Document 4).

JP2003-17791A. Japanese Patent Laid-Open No. 59-14914. Japanese Patent Application Laid-Open No. 11-251265. Japanese Patent Application Laid-Open No. 2008-60478.

  However, the present inventors have found that the cleavage problem can be improved by forming a cleavage guide groove having a depth of about 2 μm to 10 μm, but the following problems occur.

  Since nitride semiconductors do not have an effective wet etching technique, dry etching is generally used to form ridges or grooves. However, when dry etching is performed, a damage layer is formed on the surface of the nitride semiconductor. It is known that a nitride semiconductor damage layer usually becomes n-type due to the influence of nitrogen (N) vacancies and interface states.

  When deep cleaved guide grooves are formed by dry etching on both sides of the ridge stripe along the front end face and the rear end face, a dry etching surface is formed from the side walls of the ridge stripe to the cleaved guide grooves. For this reason, it is presumed that a continuous n-type surface is formed from the side wall of the ridge stripe to the cleavage guide groove. When the p-type electrode formed on the upper surface of the ridge stripe comes into contact with the side wall of the ridge stripe even a little, a minute current path is formed through the Schottky barrier. The depth of the cleavage guide groove is about 2 μm to 10 μm and is deeper than the active layer, so that the minute leak path is in contact with the active layer, the electron barrier layer, and further the n-type semiconductor layer. This causes a problem that a minute leak current is generated, the characteristics are deteriorated, and the reliability is lowered.

  An object of the present invention is to solve the above problems and to realize a nitride semiconductor laser device that can be easily cleaved and suppresses a minute leak current.

  In order to achieve the above object, the present invention has a semiconductor laser device in which the ridge portion and the cleavage guide groove are separated from each other by an unetched surface.

  Specifically, a semiconductor laser device according to the present invention includes an n-type cladding layer, an active layer, and a p-type cladding layer that are sequentially stacked on a substrate, and includes a semiconductor layer stack that constitutes a resonator. The laminate includes a ridge portion extending in a stripe shape between a front end surface that emits light and a rear end surface opposite to the front end surface, a first groove portion formed on both sides of the ridge portion, and a ridge formed by the first groove portion. A pedestal part separated from the first part, and a second groove part formed separately in the region including the front end face and the rear end face in the pedestal part, the second groove part having a depth greater than that of the first groove part. It is also characterized by deepness.

  The semiconductor laser device of the present invention includes a first groove portion and a second groove portion that are respectively formed in regions including the front end surface and the rear end surface of the pedestal portion. For this reason, since the second groove functions as a cleavage guide groove, the primary cleavage of the wafer can be facilitated. Further, since the second groove portion is separated from the first groove portion, a leak path from the side wall of the ridge portion to the second groove portion is hardly formed. Accordingly, it is possible to suppress deterioration of light emission characteristics and deterioration of reliability due to generation of leakage current.

  In the semiconductor laser device of the present invention, the second groove may be deep enough to reach the active layer. With such a configuration, the second groove portion functions sufficiently as a cleavage guide groove.

  In the semiconductor laser device of the present invention, the depth of the second groove may be 2 μm or more.

  In the semiconductor laser device of the present invention, a plurality of second groove portions may be formed on both sides of the ridge portion. With such a configuration, the cleavage guide function of the second groove can be improved without increasing the leakage current.

  In the semiconductor laser device of the present invention, the bottom surface and the side wall of the second groove may be covered with a dielectric layer.

  In the semiconductor laser device of the present invention, the first groove may have a depth that does not reach the active layer.

  In the semiconductor laser device of the present invention, the semiconductor layer stack may include an electron barrier layer formed between the active layer and the p-type cladding layer, and the first groove may have a depth that does not reach the electron barrier layer. In this case, the electron barrier layer may have a larger band gap than the p-type cladding layer. With such a configuration, the dry etching surface of the first groove portion does not reach the active layer or the electron barrier layer, and it is possible to prevent deterioration in device characteristics and reliability.

  In the semiconductor laser device of the present invention, the upper surface of the pedestal portion may be formed at a position equal to or higher than the upper surface of the ridge portion.

  In the semiconductor laser device of the present invention, the upper surface of the pedestal portion may be a non-etched surface.

  In the semiconductor laser device of the present invention, the uppermost layer constituting the pedestal portion and the uppermost layer constituting the ridge portion may be the same layer.

  In the semiconductor laser device of the present invention, the semiconductor layer stack includes a p-type contact layer, and the uppermost layer constituting the pedestal portion and the uppermost layer constituting the ridge portion may be p-type contact layers.

  In the semiconductor laser device of the present invention, the pedestal may be configured such that the upper surface is covered with a dielectric layer. With this configuration, the surface of the semiconductor layer in the pedestal portion is not etched and protected by the dielectric layer, so that the surface of the semiconductor layer is not made n-type due to dry etching damage or other factors. For this reason, the etching surface of the first groove portion and the second groove portion becomes an n-pn junction separated by the p-type portion of the pedestal portion, and the leak path can be cut.

  In the semiconductor laser device of the present invention, the semiconductor layer stack includes a side surface parallel to the ridge portion and a third groove portion formed in a region including the side surface and extending in parallel with the ridge portion, and the third groove portion is a pedestal portion. Therefore, the first groove portion may be separated from the first groove portion. With such a configuration, the left and right end face portions of the element formed by secondary cleavage can also be separated from the first groove portion and the ridge portion by the pedestal portion, and the leak path can be cut.

  In this case, the depth of the third groove portion may be the same as that of the second groove portion. With such a configuration, the second groove portion and the third groove portion can be formed simultaneously, and the process can be simplified.

  The bottom surface and the side wall of the third groove may be covered with a dielectric layer.

  In the semiconductor laser device of the present invention, the third groove portion may be continuous with the second groove portion.

  The semiconductor laser device of the present invention may further include a p-type electrode formed on the upper surface of the ridge portion, and the p-type electrode may be separated from the front end face and the rear end face. With such a configuration, the current injection portion can be separated from the front end surface and the rear end surface of the element, so that leakage current flowing through the front end surface and the rear end surface can be suppressed.

  According to the semiconductor laser of the present invention, a nitride semiconductor laser device that can be easily cleaved and suppresses a minute leak current can be realized.

(A)-(c) shows the semiconductor laser device which concerns on 1st Embodiment, (a) is a top view, (b) is sectional drawing in the Ib-Ib line, (c) is Ic- It is sectional drawing in Ic line. It is a top view which shows 1 process of the manufacturing method of the semiconductor laser apparatus concerning 1st Embodiment. It is a characteristic view which shows an example of a current-voltage characteristic and a current-light output characteristic. It is sectional drawing which expands and shows a part of semiconductor laser apparatus concerning 1st Embodiment. It is a characteristic view which shows the correlation of reverse bias leak current and ESD breakdown voltage. It is a characteristic view which shows the correlation of a reverse bias leak current and a COD destruction output. It is a Weibull plot of a cumulative failure rate. It is a top view which shows the modification of the semiconductor laser apparatus which concerns on 1st Embodiment. (A)-(c) shows the modification of the semiconductor laser apparatus which concerns on 1st Embodiment, (a) is a top view, (b) is sectional drawing in the IXb-IXb line | wire, (c) These are sectional views along the line IXc-IXc. It is a top view which shows the modification of the semiconductor laser apparatus which concerns on 1st Embodiment. It is a top view which shows the modification of the semiconductor laser apparatus which concerns on 1st Embodiment. (A)-(c) shows the semiconductor laser device concerning 2nd Embodiment, (a) is a top view, (b) is sectional drawing in the XIIb-XIIb line, (c) is XIIc- It is sectional drawing in a XIIc line.

  In the present disclosure, the front end surface is an end surface having a large light output among the two end surfaces of the resonator, and the rear end surface is an end surface having a smaller light output than the front end surface opposite to the front end surface.

(First embodiment)
A first embodiment will be described with reference to the drawings. 1A to 1C are semiconductor laser devices according to the first embodiment, FIG. 1A shows a planar configuration, FIG. 1B shows a cross-sectional configuration taken along line Ib-Ib in FIG. (C) has shown the cross-sectional structure in the Ic-Ic line | wire of (a). As shown in FIG. 1, the semiconductor laser device of this embodiment is a ridge type semiconductor laser device using a nitride semiconductor.

A semiconductor layer stack 100 is formed on a substrate 101 made of n-type GaN or the like. The semiconductor layer stack 100 includes an n-type GaN layer 102, an n-type cladding layer 103, an n-type guide layer 104, an active layer 105, a p-type guide layer 106, and p-type AlGaN, which are sequentially formed on a substrate 101. An electron barrier layer 107, a p-type cladding layer 108, and a p-type contact layer (not shown) are included. A part of the p-type cladding layer 108 is processed into a ridge stripe shape, and a ridge waveguide including a ridge portion 110 extending in the resonator length direction is formed. A dielectric layer 109 made of SiO ₂ having an opening exposing the upper surface of the ridge 110 is formed on the p-type cladding layer 108. A p-type electrode 115 is formed on the ridge portion 110 exposed from the dielectric layer 109. A pad electrode 116 connected to the p-type electrode 115 is formed on the dielectric layer 109. An n-type electrode 117 is formed on the semiconductor layer stack 100 of the substrate 101 and the surface (back surface) on the range side.

  A pedestal portion 113 separated from the ridge portion 110 by the first groove portion 112 is formed on both sides of the ridge waveguide. The position of the upper surface of the pedestal portion 113 is the same position as the upper surface of the ridge portion 110. A second groove 114 is formed in a region including a front end surface 118 that emits light and a rear end surface 119 opposite to the front end surface 118 in the pedestal portion 113. The second groove 114 is formed along the resonator width direction intersecting the resonator length direction, and the second groove 114 is a trace of the cleavage guide groove when the wafer is cleaved. Further, the first groove 112 and the second groove 114 are separated.

  A method for manufacturing the semiconductor laser device shown in FIG. 1 will be described below.

(Crystal growth process)
First, an n-GaN buffer layer (not shown) is formed on a substrate 101 made of n-type GaN having a carrier concentration of about 10 ¹⁸ cm ^{−3 by} metal organic chemical vapor deposition (MOCVD). After forming 200 nm, n-type GaN layer 102 having a thickness of 1 μm, n-type cladding layer 103 made of n-Al _0.03 Ga _0.97 N having a thickness of 2.5 μm, and n-GaN made of n-GaN having a thickness of 150 nm. A type guide layer 104, an active layer 105 having a triple quantum well structure composed of an In _0.10 Ga _0.90 N well layer having a thickness of 3 nm and an In _0.02 Ga _0.98 N barrier layer having a thickness of 7.5 nm, and a p-type having a thickness of 120 nm. A p-type guide layer 106 made of GaN, an electron barrier layer 107 made of p-Al _0.20 Ga _0.80 N having a thickness of 20 nm, and a p-type cladding layer 1 made of p-Al _0.03 Ga _0.97 N having a thickness of 0.5 μm. 08, a contact layer (not shown) made of p-GaN having a thickness of 10 nm is sequentially formed. The n-type layer is doped with Si as a donor impurity to about 5 × 10 ¹⁷ cm ⁻³ . The p-type layer is doped with about 1 × 10 ¹⁹ cm ⁻³ of Mg as an acceptor impurity. The outermost contact layer is doped with Mg at a high concentration of about 1 × 10 ²⁰ cm ⁻³ . The electron barrier layer 107 is a layer whose band gap is increased by increasing the Al composition to 20%. Since electrons flowing in the conduction band have a higher mobility than holes flowing in the valence band, they pass through the active layer, and there is a possibility of non-radiative recombination in a layer other than the active layer. However, non-radiative recombination can be suppressed by forming the electron barrier layer 107. Note that the structure of the semiconductor layer in this embodiment is an example, and the structure and growth method of the semiconductor layer are not limited to this. Further, the substrate may be sapphire or silicon carbide as long as the semiconductor layer can be grown.

(Stripe waveguide formation process)
Next, after depositing a SiO ₂ film to a thickness of 200 nm by chemical vapor deposition (CVD), heat treatment is performed at 850 ° C. for 30 minutes in a nitrogen (N ₂ ) atmosphere, and Mg as an acceptor impurity in the p-type layer. Activate. Subsequently, a SiO ₂ mask is formed in the regions to be the ridge portion 110 and the pedestal portion 113 by photolithography and reactive ion etching (RIE). Thereafter, the semiconductor layer is etched by about 0.5 μm by inductively coupled plasma (ICP) dry etching using Cl ₂ gas or SiCl ₄ gas using SiO ₂ as a mask to form the first groove 112. . Thereby, the ridge portion 110 and the pedestal portion 113 separated from the ridge portion 110 by the first groove portion 112 are formed. The etching amount can be controlled with high accuracy by using interference waveform monitoring using an ultraviolet light source during etching. In the present embodiment, the width of the bottom of the ridge 110 is about 1.4 μm, and the width of the first groove that separates the ridge 110 and the pedestal 113 is 7 μm.

(Cleaving guide groove forming process)
Subsequently, the SiO ₂ film used for the mask is removed using a buffered hydrofluoric acid solution (BHF), and then the SiO ₂ film is deposited again to 800 nm. Thereafter, the SiO ₂ film in the region for forming the cleavage guide groove is removed by photolithography and RIE. Thereafter, the semiconductor layer is etched by about 3 μm by ICP dry etching using Cl ₂ gas or SiCl ₄ gas using the SiO ₂ film as a mask to form a cleavage guide groove. In the present embodiment, the width of the cleavage guide groove in the resonator length direction is about 2 μm, and the length in the resonator width direction is about 150 μm. In order to improve the cleavage property, the cleavage guide groove has a narrow width in the resonator length direction at both ends, and the angle of the tip is about 60 degrees. Further, it is separated from the first groove portion 112 and formed on the pedestal portion 113, and the distance from the ridge portion 110 is about 20 μm.

(Dielectric block layer and p-type electrode forming step)
Subsequently, the SiO ₂ film used for the mask is removed using a buffered hydrofluoric acid solution (BHF), and then a dielectric layer 109 made of the SiO ₂ film is again deposited on the entire surface of the wafer by 300 nm. An opening is formed in the dielectric layer 109 immediately above the ridge 110 by wet etching using photolithography and a buffered hydrofluoric acid solution (BHF). A p-type electrode 115 made of palladium (Pd) / platinum (Pt) is formed in the formed opening by electron beam evaporation. The thicknesses of the Pd film and the Pt film are 40 nm and 35 nm, respectively, and vapor deposition is performed with the substrate heated to 70 ° C. The opening may be formed using a resist etch back technique. Thereafter, the contact resistance of the p-type electrode 115 can be reduced to 2 × 10 ⁻⁴ Ωcm ² or less by applying a heat treatment at 400 ° C. If the temperature at which Pd and Pt are deposited is about 70 ° C. to 100 ° C., the contact resistance is most improved and the adhesion is improved. Considering the heat resistance of the resist used for patterning, the deposition temperature of Pd and Pt is preferably about 70 ° C.

(Pad electrode formation process)
Subsequently, a pad electrode 116 for wiring made of titanium (Ti) / platinum (Pt) / gold (Au) is formed on the p-electrode by photolithography and electron beam evaporation. The film thicknesses of the Ti film, Pt film, and Au film may be 50 nm, 35 nm, and 500 nm, respectively. The pad electrode 116 for wiring is preferably not formed on the end face part because the Au film is thick and hinders cleavage.

(Back electrode forming process)
Next, after grinding and polishing the back surface of the substrate 101 to a thickness of about 100 μm, an n-type electrode 117 made of Ti / Pt / Au is formed on the back surface of the substrate 101. The film thicknesses of the Ti film, Pt film, and Au film may be 15 nm, 35 nm, and 300 nm, respectively. As a result, the contact resistance of the n-type electrode 117 can be reduced to 1 × 10 ⁻⁴ Ωcm ² or less. As a recognition pattern at the time of cleavage and assembly, it is preferable to form an electrode pattern by etching only the Au film by photolithography and wet etching.

(Cleavage and assembly process)
Through the steps as described above, a wafer in which the ridge portion 110, the pedestal portion 113, the first groove portion 112, the cleavage guide groove 114A, and the pad electrode 116 are disposed as shown in FIG. 2 is obtained. Next, the obtained wafer is primarily cleaved to form a resonator end face. The primary cleavage is braked along the cleavage guide groove 114A. For this reason, the second groove part 114 in which the cleavage guide groove 114A is halved is formed on the front end face 118 and the rear end face 119 of each resonator. Subsequently, a multilayer dielectric reflective film having a reflectance of about 12% is formed on the front end face 118, and a multilayer dielectric reflective film having a reflectance of about 95% is formed on the rear end face 119. Thereafter, secondary cleaving is performed in the cavity length direction, and the semiconductor laser device using a nitride semiconductor can be manufactured by mounting and wiring in a CAN package.

  By forming the cleavage guide groove, the cleavage property can be improved. However, in the case of a nitride semiconductor, since there is no effective wet etching method, dry etching is used for the cleavage guide groove. When dry etching is performed, a damage layer is formed on the surface of the nitride semiconductor. The nitride semiconductor damage layer is usually n-type due to nitrogen vacancies and interface states. Such a damage layer is generated not only when the cleavage guide groove is formed but also when the ridge portion is formed. When a cleavage guide groove is formed such that the side surface of the ridge portion to the cleavage guide groove is a continuous dry etching surface, the surface from the side surface of the ridge portion to the cleavage guide groove becomes a continuous n-type surface. For this reason, when the p-type electrode formed on the upper surface of the ridge portion contacts the side wall of the ridge portion even a little, a minute current path is formed via the Schottky barrier. The cleavage guide groove needs to be 2 μm to 10 μm deep, and is deeper than the active layer 105. Therefore, the minute leak path is connected to the electron barrier layer 107, the active layer 105, and the n-type semiconductor layer such as the n-type GaN layer 102. The inventors of the present application have found that when the minute leak path is connected to the active layer or the like, the minute leak current flowing through the minute leak path causes deterioration of the characteristics or reliability of the semiconductor laser device.

  FIG. 3 shows current-voltage characteristics and current-light output characteristics of the semiconductor laser device. As shown in FIG. 3, in the case of a semiconductor laser device in which a groove that penetrates the electron barrier layer and the active layer is not separated from the ridge near the ridge, a current leak occurs in a region near the oscillation threshold. A voltage drop and an increase in the oscillation threshold were observed. A semiconductor laser device having such characteristics is less reliable. Since the magnitude of the current flowing through the leak path depends on the total length of the leak path, the influence of the leak path is reduced when the distance between the groove and the ridge is increased. When the groove is formed at a distance of about 20 μm from the ridge, no definite characteristic deterioration as shown in FIG. 3 is observed. However, the leakage current at the time of reverse bias becomes larger than that in the case where no groove is formed, and the COD (Instantaneous Optical Damage) level and ESD (Electrostatic Discharge) breakdown voltage are also lowered. In the case of a low-power laser device with an output of several tens of mW, the current flowing through the entire element is also small. For this reason, the current flowing in the leak path is also small, and even if the groove is formed, the influence on the reliability of the semiconductor laser device is small. However, in the case of a high-power laser device with an output exceeding 300 mW, the current and voltage during operation increase, and the influence of the leakage path increases.

  However, in the semiconductor laser device of this embodiment, a pedestal portion 113 is provided in a region outside the ridge waveguide, and a cleavage guide groove 114A is formed in the pedestal portion 113. Therefore, as shown in FIG. 4, the upper surface of the pedestal portion 113 is not dry-etched, and the n-type layer 201 generated by dry etching is not generated. Therefore, the leak path through the n-type layer 201 is divided by the p-type layer on the non-etched surface of the pedestal 113. As a result, leakage current flowing from the ridge portion to the electron barrier layer 107, the active layer 105, and the n-type semiconductor layer 202 can be suppressed, and reliability during high output operation can be improved.

  FIG. 5 shows the relationship between the leakage current during reverse bias and the ESD breakdown voltage. The semiconductor laser device of this embodiment in which the leak path is divided by the pedestal portion 113 can suppress the leakage current more than the conventional semiconductor laser device that does not have the pedestal portion. As a result, the ESD breakdown voltage was improved. FIG. 6 shows the relationship between the leakage current during reverse bias and the COD breakdown output. Similar to the ESD breakdown voltage, it was confirmed that the COD breakdown output was improved by suppressing the leakage current. The interval between the ridge portion of the semiconductor laser device used for the measurement and the cleavage guide groove was 20 μm.

  FIG. 7 shows the result of Weibull plotting of the cumulative failure rate during the reliability test (output CW 160 mW, 75 ° C.). The semiconductor laser device of this embodiment has a mean time to failure (MTTF) that is approximately three times as large as that of the conventional semiconductor laser device, and can ensure reliability of 3,000 hours.

  In the present embodiment, the depth of the second groove 114 formed from the cleavage guide groove 114A is 3 μm, but the depth of the second groove 114 may be changed as appropriate. However, as the depth of the second groove 114 is deeper, the cleavage assisting function tends to be improved, and an effect is hardly obtained at 1 μm or less. Therefore, the depth of the second groove 114 is preferably 2 μm or more. If the depth of the second groove portion 114 is shallower than that of the active layer 105 and the electron barrier layer 107, the leakage current should be able to be suppressed without forming the pedestal portion 113. However, the active layer 105 and the electron barrier layer 107 are usually formed at a position of 0.5 to 1.0 μm from the surface of the semiconductor layer stack. Accordingly, the distance from the bottom surface of the ridge portion 110 to the active layer 105 is only 0.1 μm to 0.2 μm, and a shallow groove portion that does not penetrate these layers cannot exhibit the cleavage assist function. In addition, the cleaving assist function is improved as the depth of the groove is deeper. However, if the depth is too deep, residues in the process are likely to accumulate or the risk of wafer cracking increases. The maximum is preferably about 5 μm.

  In the present embodiment, the depth of the first groove portion 112 is set to about 0.5 μm, but this depth may be appropriately changed as long as the depth does not penetrate the active layer 105 and the electron barrier layer 107. When the first groove 112 penetrates the electron barrier layer 107 and the active layer 105, the surface to be etched of the first groove 112 is connected to the active layer 105 and the electron barrier layer 107 to form a leak path. In addition, since the distance to the p-type electrode 115 is shorter than the second groove 114, the leakage current is also very large. The strength of light confinement by the dielectric layer 109 formed on the bottom and side walls of the ridge 110 is determined by the depth of the first groove 112. The distance from the active layer 105 to the bottom surface of the ridge 110 is called the remaining thickness and is an important design factor that determines the horizontal spread angle. In order to realize this horizontal divergence angle as designed and to realize a high-reliability high-power laser, the first groove 112 (the bottom surface of the ridge stripe waveguide) is designed not to penetrate the electron barrier layer. This is very important.

  In the present embodiment, by forming the first groove portion 112, the ridge portion 110 and the pedestal portion 113 are formed simultaneously. Therefore, the surfaces of the semiconductor layers constituting the pedestal portion 113 and the ridge portion 110 have the same height. However, the dielectric layer 109 has an opening on the ridge 110. For this reason, the outermost surface of the pedestal 113 is higher than the outermost surface of the ridge 110 by the thickness of the dielectric layer 109. As a result, the effect of protecting the ridge portion 110 during assembly mounting is increased, and the yield of the semiconductor laser device can be improved. Further, since the surface of the pedestal 113 and the side walls and bottom of the first groove 112 are protected by the dielectric layer 109, it is possible to prevent a new leak path from being formed by particles attached to the surface of the pedestal 113. it can.

In the present embodiment, the surface layer of the pedestal portion 113 is the same p-type contact layer as the surface layer of the ridge portion 110. Since the p-type contact layer is a layer doped with Mg at a high concentration of about 10 ²⁰ cm ³ , it is assumed that the p-type contact layer is a layer that is difficult to be n-type, and depends on the surface n-type layer of the first groove 112 and the second groove 114. This layer is suitable for dividing the leak path.

  In the present embodiment, one second groove portion 114 is provided on each side of the ridge portion 110 on the front end surface 118 and the rear end surface 119, but a plurality of second groove portions 114 are provided on both sides of the ridge portion as shown in FIG. May be formed. By setting the tip of the cleavage guide groove to an appropriate angle, cracks generated during the primary cleavage can be concentrated on the tip of the groove. For this reason, the precision of cleavage can be improved by increasing the number of front-end | tip parts. Although FIG. 8 shows an example in which three cleavage guide grooves are formed between adjacent ridge portions 110, the number of cleavage guide grooves formed between the ridge portions 110 is 2 in consideration of the resonator width and the like. It is preferable that the number is about 5 or so.

  In addition, as shown in FIG. 9, the third groove 130 may be formed on the left and right side surfaces of the semiconductor layer stack 100 that becomes the resonator. Since the side surface of the resonator is different from the cleavage direction of the crystal, a method of dividing using a scribe by a diamond needle or a laser beam is common. However, a leak path is likely to occur due to physical destruction when the scribe is formed. By forming a scribe in the third groove part 130 separated from the first groove part 112 by the pedestal part 113, it is possible to prevent the occurrence of a leak path due to the destruction of the active layer and the pn junction part. Since the third groove 130 is farthest from the ridge waveguide, it is less susceptible to leakage than the second groove 114. However, if the resonator width is reduced to reduce the cost of the semiconductor laser device, the ridge waveguide is shifted from the center of the semiconductor laser device as shown in FIG. 10 in order to secure the wire bonding portion. Is required. In such an arrangement, the distance from the ridge waveguide portion of the second groove portion 114 and the third groove portion 130 is almost the same, and the leak path generated by the third groove portion 130 is increased by the size of the groove portion. In such a case, the leakage path can be greatly suppressed by providing the third groove portion 130 separated by the pedestal portion 113. The depth of the third groove 130 may be any depth that penetrates the active layer 105 and reaches the n-type layer. However, in terms of the number of processes, the groove having the same depth as the second groove 114 is formed in the second groove 114. It is preferable to form it simultaneously. In addition, as shown in FIG. 11, the second groove portion 114 and the third groove portion 130 may be formed continuously and integrally.

  By introducing the leak suppressing structure as in the present embodiment, it is possible to prevent the current injected from the p-type electrode formed on the upper part of the ridge waveguide from flowing as a leak path on the dry etching surface of the groove surface. Therefore, the leakage current of the semiconductor laser device can be suppressed, and a high output and high reliability nitride semiconductor laser can be manufactured.

(Second Embodiment)
Hereinafter, a second embodiment will be described with reference to the drawings. 12A to 12C show a semiconductor laser device according to the second embodiment, where FIG. 12A shows a planar configuration, FIG. 12B shows a cross-sectional configuration taken along line XIIb-XIIb in FIG. (C) has shown the cross-sectional structure in the XIIc-XIIc line | wire of (a). In FIG. 12, the same components as those in FIG.

  As shown in FIG. 12, in the semiconductor laser device of this embodiment, the p-type electrode 115 is formed with a distance from the front end face 118 and the rear end face 119. The p-type electrode 115 is formed 5 μm away from the front end face 118 and the rear end face 119, and the end face non-injection portion 140 is secured. Also on the left and right end faces of the resonator, third groove portions 130 having the same depth as the second groove portions are formed entirely along the left and right side surfaces.

  Since the method of manufacturing the semiconductor laser of this embodiment is almost the same as that of the first embodiment, the details are omitted. The difference from the first embodiment is that the p-type electrode 115 is formed at a certain distance from the front end face 118 and the rear end face 119. Since the front end face 118 and the rear end face 119 of the resonator are formed by cleaving the crystal, there is no leak path due to physical destruction unlike the side face of the resonator that needs to be formed using scribe. However, there is a possibility that a minute surface defect or a damage layer at the time of forming the end face coating film becomes a leak path. By securing the end surface non-injection portion 140 without forming the p-type electrode 115 in the vicinity of the front end surface 118 and the rear end surface 119, leakage from the front end surface 118 and the rear end surface 119 can be suppressed, and leakage current can be further reduced. It was found that the COD level was improved by about 100 mW.

  In this embodiment, the length of the end surface non-injection portion 140 is 5 μm, but the length of the end surface non-injection portion 140 may be changed as appropriate. It is considered that the leakage current can be suppressed as the length of the end face non-injection part 140 is increased. However, if the length is too long, there will be no current injection and the saturable absorption region with the gain and loss of the waveguide will increase, so that the oscillation threshold will increase and the slope efficiency will jump greatly. Therefore, it is preferable that the end surface non-injection part 140 has a length of about 5 μm to 10 μm on each side of the front end surface 118 and the rear end surface 119. The ratio of the end face non-injection portion 140 to the resonator length is preferably about 5% to 30%.

  Further, by adopting an end face window structure that eliminates light absorption in the end face portion vicinity region, it is possible to suppress an increase in oscillation threshold and a jump in slope efficiency, so that the length of the end face non-injection portion 140 is further increased, Leakage current can be reduced. Since the end face temperature can be suppressed by the end face window structure, a higher output nitride semiconductor laser device can be realized.

  Although FIG. 12 shows an example in which the second groove portion 114 and the third groove portion 130 are formed integrally, it is not necessary to form the second groove portion 114 and the third groove portion 130 integrally. Further, the third groove portion 130 may not be formed.

  By introducing the end face non-injection portion according to the second embodiment, it is possible to prevent the leakage current flowing from the p-type electrode formed on the top of the ridge waveguide from flowing through the front end face and the rear end face as a leak path. . Therefore, a high-output and high-reliability nitride semiconductor laser in which the leakage current of the semiconductor laser device is suppressed can be manufactured.

  The semiconductor laser device according to the present invention can realize a nitride semiconductor laser device that can be easily cleaved and suppresses a minute leakage current, and can be used as a light source for writing and reading a high-density optical disk using blue light or the like. It is useful as a reliable blue-violet semiconductor laser device.

DESCRIPTION OF SYMBOLS 100 Semiconductor layer laminated body 101 Substrate 102 n-type GaN layer 103 n-type clad layer 104 n-type guide layer 105 Active layer 106 p-type guide layer 107 Electron barrier layer 108 p-type clad layer 109 Dielectric layer 110 Ridge part 112 First groove part 113 Pedestal part 114 Second groove part 114A Cleaving guide groove 115 p-type electrode 116 pad electrode 117 n-type electrode 118 front end face 119 rear end face 130 third groove part 140 end face non-injection part 201 n-type layer 202 n-type semiconductor layer

Claims (18)

A semiconductor layer stack comprising an n-type cladding layer, an active layer and a p-type cladding layer sequentially stacked on a substrate, and constituting a resonator;
The semiconductor layer stack is
A ridge portion extending in a stripe shape between a front end face that emits light and a rear end face opposite to the front end face;
A first groove formed on both sides of the ridge,
A pedestal portion separated from the ridge portion by the first groove portion;
The pedestal portion is formed in each region including the front end surface and the rear end surface, and has a second groove portion separated from the first groove portion,
2. The semiconductor laser device according to claim 1, wherein a depth of the second groove is deeper than that of the first groove.   The semiconductor laser device according to claim 1, wherein the second groove has a depth reaching the active layer.   The semiconductor laser device according to claim 2, wherein the depth of the second groove is 2 μm or more.   4. The semiconductor laser device according to claim 1, wherein a plurality of the second groove portions are formed on both sides of the ridge portion. 5.   5. The semiconductor laser device according to claim 1, wherein a bottom surface and a side wall of the second groove are covered with a dielectric layer.   6. The semiconductor laser device according to claim 1, wherein the first groove has a depth that does not reach the active layer. The semiconductor layer stack includes an electron barrier layer formed between the active layer and a p-type cladding layer,
The semiconductor laser device according to claim 1, wherein the first groove has a depth that does not reach the electron barrier layer.   The semiconductor laser device according to claim 7, wherein the electron barrier layer has a band gap larger than that of the p-type cladding layer.   9. The semiconductor laser device according to claim 1, wherein the upper surface of the pedestal portion is formed at a position equal to or higher than the upper surface of the ridge portion.   The semiconductor laser device according to claim 1, wherein an upper surface of the pedestal portion is a non-etched surface.   11. The semiconductor laser device according to claim 1, wherein an uppermost layer constituting the pedestal portion and an uppermost layer constituting the ridge portion are the same layer. The semiconductor layer stack includes a p-type contact layer,
12. The semiconductor laser device according to claim 11, wherein the uppermost layer constituting the pedestal portion and the uppermost layer constituting the ridge portion are the p-type contact layer.   The semiconductor laser device according to claim 1, wherein an upper surface of the pedestal portion is covered with a dielectric layer. The semiconductor layer stack is
A side surface parallel to the ridge portion;
A third groove formed in a region including the side surface and extending in parallel with the ridge;
The semiconductor laser device according to claim 1, wherein the third groove portion is separated from the first groove portion by the pedestal portion.   The semiconductor laser device according to claim 14, wherein a depth of the third groove portion is the same as that of the second groove portion.   16. The semiconductor laser device according to claim 14, wherein a bottom surface and a side wall portion of the third groove portion are covered with a dielectric layer.   17. The semiconductor laser device according to claim 14, wherein the third groove portion is continuous with the second groove portion. A p-type electrode formed on the upper surface of the ridge portion;
The semiconductor laser device according to claim 1, wherein the p-type electrode is separated from the front end surface and the rear end surface.

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