JP2005268754A - Semiconductor laser element, manufacturing method thereof, optical disk device,, and optical transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low consumption power semiconductor laser element and its manufacturing method capable of being inexpensively manufactured by preventing light from leaking to an electrode side and of low threshold current oscillation and high efficiency operation. <P>SOLUTION: There are formed on an n-GaAs substrate 101 a multiple distortion quantum well active layer 106, a second conductivity type semiconductor layer group (p-AlGaAs first upper cladding layer 108, p-AlGaAs second upper cladding layer 109, p-GaAs etching stop layer 110, p-AlGaAs third upper cladding layer 111, p-GaAs contact layer 112, and p<SP>+</SP>-GaAs contact layer 113). The p-side electrode 114 of a multiple structure formed on the surface of the second conductivity type semiconductor layer group on the side of an upper ridge 130 makes contact with the side surface of the ridge 130 and with the surface of the second conductivity type semiconductor layer group in the vicinity of the ridge 130. In a lowermost layer of the p-side electrode 114, a refractive index to the oscillated laser light is assumed to be ≤1.0. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a semiconductor laser element, a method for manufacturing a semiconductor laser element, an optical disc apparatus, and an optical transmission system, and more particularly to a semiconductor laser element used in an optical disc apparatus and an optical transmission system and a method for manufacturing the same.

  A ridge waveguide semiconductor laser element having a ridge portion on the active layer and capable of being manufactured in one crystal growth process is simpler in manufacturing process than a ridge buried semiconductor laser element requiring three crystal growth processes. Therefore, there is an advantage that a semiconductor laser device can be manufactured at low cost.

  Among such ridge waveguide semiconductor laser elements, Schottky junctions that can be manufactured at a lower cost than ridge waveguide semiconductor laser elements that perform current confinement using an insulating film known as an air ridge type are used. FIG. 7 shows a conventional example of a ridge waveguide type semiconductor laser device that performs current confinement (see, for example, JP-A-4-111375 (Patent Document 1)).

  This semiconductor laser device is manufactured as follows. First, as shown in FIG. 7, an n-InGaP cladding layer 402, an InGaAs / GaAs strained quantum well active layer 403, and a p-InGaP cladding are formed on an n-GaAs substrate 401 by metal organic chemical vapor deposition (MOCVD). A layer 404 and a p-InGaAs contact layer 405 are sequentially stacked. Next, etching is performed halfway through the p-InGaP cladding layer 404 by a technique such as photolithography to form a mesa, and then Ti / Pt / Au is used as the p electrode 406 in order from the lower layer, and Au-Ge is used as the n electrode 407. -Ni / Au is sequentially deposited. When a current is passed through the device thus fabricated, a Schottky junction 408 is formed between the p-InGaP cladding layer 404 and the p-electrode 406, and the p-electrode 406 and the p-InGaAs contact layer 405 are connected to each other. Current flows only between them, and current confinement is performed.

  The above-described manufacturing method of the ridge-embedded semiconductor laser device requires three crystal growth steps, but the configuration like the conventional ridge waveguide semiconductor laser device described above requires only one crystal growth step. Since it can be manufactured and no insulating film or the like is used for current confinement, the manufacturing process is greatly simplified, which is overwhelmingly less expensive than conventional ridge embedded semiconductor laser devices. A ridge waveguide semiconductor laser device that can be manufactured is provided.

  However, the above-described ridge waveguide semiconductor laser device has the following problems. That is, unlike the above-described air ridge type semiconductor laser device that prevents current from flowing by having an insulating film at the interface between the electrode and the semiconductor layer, the current confinement is performed using a Schottky junction without the insulating film described above. In the conventional ridge waveguide semiconductor laser device, the electrode is in direct contact with the side surface of the ridge portion and the surface of the cladding layer extending outward from the ridge portion. At this time, depending on the relationship between the refractive index of the semiconductor material constituting the semiconductor laser element and the refractive index of the electrode material, the oscillation laser light distribution leaks to the electrode side formed on the side surface of the ridge portion and the surface of the cladding layer near the ridge portion. It turns out that it becomes an easy shape.

  For example, the refractive index of the electrode material used in the conventional ridge waveguide semiconductor laser element is such that Ti in contact with the semiconductor material is approximately 3.1 to 3.6 in the wavelength range of 800 nm to 1.5 μm. Pt provided on the upper side of Ti is 3.0 to 5.5 in the same wavelength range of 800 nm to 1.5 μm. On the other hand, the effective refractive index in the vertical direction outside the ridge is also about 3.2, for example, and the refractive index values of both are very close to each other.

  As described above, when the effective refractive index in the vertical direction outside the ridge portion and the value of the refractive index of the electrode material directly formed on the semiconductor layer are close to each other, light may easily leak in the electrode direction.

When light leaks to the electrode, the metal material generally has a light absorption coefficient that is 10 ⁴ to 10 ⁵ times higher than that of the semiconductor material. Therefore, the metal material constituting the electrode is very large in light. It has been found that problems such as an absorption component increase internal loss, increase the oscillation threshold current of the semiconductor laser element, and decrease the slope efficiency.
Japanese Patent Laid-Open No. 4-111375 (page 3, FIG. 1)

  The present invention overcomes the above-mentioned problems and does not leak light to the electrode side, so that it can be manufactured at a low cost, and a low threshold current oscillation and a highly efficient operation can be achieved. It aims to provide a method.

  A further object of the present invention is to provide an optical disk apparatus and an optical transmission system using a semiconductor laser element that overcomes the above-mentioned problems.

  In order to achieve the above object, a semiconductor laser device of the present invention has at least an active layer and a second conductive type semiconductor layer group on a first conductive type substrate, and the second conductive type semiconductor layer group includes: In the ridge waveguide type semiconductor laser device in which a part of the upper side forms a stripe-shaped ridge portion, the ridge portion of the second conductivity type semiconductor layer group is formed on the second conductivity type semiconductor layer group. An upper electrode having a multilayer structure in contact with at least one of the side surfaces of the second conductive type semiconductor layer group excluding the ridge portion and the surface in the vicinity of the ridge portion, and oscillates at least in the lowest layer of the upper electrode The refractive index for laser light is 1.0 or less.

  Here, “first conductivity type” refers to one conductivity type of n-type and p-type, and “second conductivity type” refers to the other conductivity type of n-type and p-type.

  According to the semiconductor laser device having the above structure, since the refractive index of the material used for at least the lowermost layer of the upper electrode is sufficiently small as 1.0 or less, the oscillated laser light hardly leaks to the upper electrode side. It can be trapped inside. Therefore, it is possible to provide a semiconductor laser device capable of operating with low power consumption and having a low oscillation threshold current and a high slope efficiency without causing the electrode material to become a light absorption component and therefore without increasing the internal loss. .

  In one embodiment, the thickness of the lowermost layer of the upper electrode having a refractive index with respect to the oscillation laser light of 1.0 or less is preferably 30 nm or more.

  According to the configuration of the semiconductor laser device of the above-described embodiment, the lowermost layer of the upper electrode having a refractive index of 1.0 or less has a layer thickness of 30 nm or more, so that it is formed above the lowermost layer of the upper electrode. In addition, since it is almost unaffected by the refractive index of other upper electrode materials, there is no increase in internal loss, while maintaining the characteristics of low threshold current and high-efficiency oscillation, improving the reliability of the upper electrode and resistance. It is possible to optimize the structure of the upper electrode having a multilayer structure so as to reduce the value. As a result, the device characteristics can be further improved.

  According to the configuration of the semiconductor laser device of one embodiment, it is preferable that the lowermost layer of the upper electrode is made of at least one of Au, Ag, Cu, or Al.

  According to the configuration of the semiconductor laser device of the above-described embodiment, by using Ag or Cu for the lowermost layer of the upper electrode, the refractive index is 1 or less in the range of the wavelength of the oscillation laser light from at least 400 nm to more than 1.5 μm. It can be. When Au is used for the lowermost layer of the upper electrode, the refractive index can be made 1 or less in the oscillation wavelength range of 500 nm to 1.5 μm. Further, by using Al for the lowermost layer of the upper electrode, the refractive index can be made 1 or less when the wavelength of the oscillation laser light is at least 400 nm or more and 650 nm or less. The lowermost layer of the upper electrode may be an alloy containing each metal.

  In the semiconductor laser device of one embodiment, it is preferable that at least three layers of an adhesion improving layer, a diffusion prevention layer, and a low resistance layer are sequentially laminated on the lowermost layer of the upper electrode.

  Here, the “adhesion improvement layer” is a layer provided to improve the adhesion of the layer (adhesion improvement layer) above the layer (adhesion improvement layer) to the base of the layer (adhesion improvement layer). Yes, `` diffusion prevention layer '' means that the material constituting the layer provided above that layer (diffusion prevention layer) exceeds that layer (diffusion prevention layer) and is more than that layer (diffusion prevention layer) It is a layer provided to prevent diffusion to the lower side. In addition, the “low resistance layer” is a layer provided for the purpose of reducing contact resistance with respect to wiring resistance or metal wire used for electrical connection with the outside.

  According to the configuration of the semiconductor laser device of the above embodiment, the adhesion improving layer for improving the adhesion to the lowermost layer of the upper electrode and the low resistance layer are provided to prevent diffusion to the lowermost layer side. Since the diffusion prevention layer and the low resistance layer are formed, it is possible to obtain a low resistance upper electrode having good adhesion to the lowermost layer and preventing material diffusion to the lowermost layer. . As a result, an electrode configuration is provided in which the lowermost layer having a refractive index of 1.0 or less can be stably present even during long-term device operation while keeping the resistance of the upper electrode low.

In one embodiment, the uppermost portion of the ridge portion of the second conductivity type semiconductor layer group and the upper electrode form an ohmic junction, and other than the uppermost portion of the ridge portion. It is preferable that at least a part of the region and the upper electrode form a Schottky junction.

  According to the semiconductor laser device of the above embodiment, the semiconductor laser device can be manufactured in one crystal growth step and can confine current to other than the ridge portion as compared with the ridge embedded semiconductor laser device that requires three crystal growth steps. Since there is no need to provide an insulating film, the manufacturing process is greatly simplified. As a result, a ridge waveguide semiconductor laser device capable of low threshold current, high-efficiency operation and low-cost manufacturing is provided.

In the configuration of the semiconductor laser device of one embodiment, the uppermost ridge portion of the second conductive type semiconductor layer group is a high concentration semiconductor layer having a second conductive type doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more. And at least part of the region other than the uppermost portion of the ridge portion of the second conductivity type semiconductor layer group is a low concentration semiconductor layer having a second conductivity type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less, A compound layer on the high concentration side composed of a constituent element of the upper electrode and a constituent element of the high concentration semiconductor layer is formed at the interface between the upper electrode and the high concentration semiconductor layer, and the upper electrode and the low concentration semiconductor layer are formed. It is preferable that a low-concentration compound layer comprising the material of the upper electrode and the constituent elements of the low-concentration semiconductor layer is formed at the interface with the upper electrode.

According to the semiconductor laser device having the above configuration, in the ohmic junction between the high concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more and the upper electrode, a lower contact resistance can be obtained by the high concentration compound layer. At the same time, in the Schottky junction between the low concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less and the upper electrode, sufficient current confinement can be obtained by the low concentration side compound layer. Since the ohmic junction and the Schottky junction are both strengthened in this way, the crystal regrowth process of the buried layer (current blocking layer) for current confinement and the crystal regrowth of the contact layer for low contact resistance Sufficient current constriction and low contact resistance can be realized without performing a separate process, and thermal and electrical reliability is improved. Therefore, it is possible to provide a semiconductor laser element that has low power consumption and high reliability because it can operate with low threshold current and high efficiency, and that can reduce costs by simplifying the manufacturing process.

  The high-concentration semiconductor layer is provided at the top of the ridge portion, and the low-concentration semiconductor layer is provided at least in a region other than the top of the ridge portion, whereby a high-concentration semiconductor layer is formed at the top. The same upper electrode formed on the high-concentration semiconductor layer and the low-concentration semiconductor layer of the second conductivity type semiconductor layer group in the ridge portion provided with the low-concentration semiconductor layer in the region other than the uppermost portion As a result, a Schottky junction portion for current confinement and an ohmic junction portion for current injection can be formed at the same time, so that a semiconductor laser device capable of significantly reducing the manufacturing cost can be provided.

In one embodiment, a semiconductor layer of a second conductivity type having a doping concentration of at least 1 × 10 ¹⁷ cm ⁻³ or more is formed between the low concentration semiconductor layer and the active layer. Preferably it is.

According to the semiconductor laser device of the above embodiment, a second conductivity type semiconductor layer having at least a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or more is further formed between the low concentration semiconductor layer and the active layer. Thus, the layer thickness and composition of the second conductivity type semiconductor layer can be freely changed according to the required optical characteristic specifications without being restricted to maintain good Schottky junction characteristics. As a result, the degree of freedom in optical design is increased, and an increase in element resistance can be suppressed, thereby further reducing power consumption.

  The method of manufacturing a semiconductor laser device of the present invention includes a step of forming an active layer on a first conductivity type substrate, a step of forming a second conductivity type semiconductor layer group on the active layer, Removing a part of the two-conductivity-type semiconductor layer group to form a ridge portion; and a metal material having a refractive index with respect to the oscillation laser light of 1.0 or less on the second-conductivity-type semiconductor layer group. And a step of forming an upper electrode using the lowermost layer.

  According to the manufacturing method of the semiconductor laser device, since the metal material having a refractive index with respect to the oscillation laser light of 1.0 or less is used for the lowermost layer of the upper electrode, the light at the upper electrode near the ridge side surface or in the vicinity of the ridge portion is used. There is provided a method for manufacturing a semiconductor laser device with reduced power consumption because there is no problem of absorption, low threshold current oscillation, and high efficiency operation.

In one embodiment of the method for manufacturing a semiconductor laser device, in the step of forming the second conductive type semiconductor layer group, a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more is formed as the uppermost portion of the ridge portion. Forming a semiconductor layer and forming a low-concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less at least in a region other than the ridge portion, and performing a heat treatment after the step of forming the upper electrode; It is preferable to include a step of forming a compound layer at the interface between the second conductive type semiconductor layer group and the upper electrode.

According to the semiconductor laser device manufacturing method of the above embodiment, sufficient current confinement is obtained by the compound layer in the Schottky junction between the low concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less and the upper electrode. In addition, a lower contact resistance can be obtained by the compound layer in the ohmic junction between the high concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more and the upper electrode. Since the Schottky junction and ohmic junction are further enhanced in this way, low threshold current, high efficiency, and low without performing the current block layer burying regrowth step and the electrode contact layer crystal regrowth step. Power consumption operation is possible, and the cost can be reduced by simplifying the manufacturing process. Therefore, it is possible to manufacture a semiconductor laser device that can obtain a sufficient current confinement property and excellent device characteristics and can operate with low power consumption.

Also, in one embodiment of the method of manufacturing a semiconductor laser device, in the step of forming the second conductivity type semiconductor layer group, at least 1 × 10 ¹⁷ cm ⁻ between the low concentration semiconductor layer and the active layer. It is preferable to form a second conductivity type semiconductor layer having a doping concentration of ³ or more.

According to the method of manufacturing a semiconductor laser device of the above embodiment, a second conductivity type semiconductor layer having at least a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or more is further provided between the low concentration semiconductor layer and the active layer. By forming, the thickness, composition, etc. of the second conductivity type semiconductor layer can be freely changed according to the required optical characteristic specifications without being restricted to achieve good Schottky junction characteristics. Therefore, it is possible to provide a method of manufacturing a semiconductor laser device that increases the degree of freedom in optical design, suppresses an increase in device resistance, and realizes further reduction in power consumption.

  The optical disc apparatus of the present invention is characterized by using any one of the above semiconductor laser elements.

  According to the above optical disk apparatus, it is possible to provide an optical disk apparatus that can be operated at lower cost and with lower power consumption than a conventional optical disk apparatus.

  The optical transmission system of the present invention is characterized by using any one of the above semiconductor laser elements.

  According to the above-described optical transmission system, it is possible to provide an optical transmission module that is cheaper and consumes less power than conventional ones, and it is possible to reduce the price of the optical transmission system.

  As is clear from the above, according to the semiconductor laser device of the present invention, in the ridge waveguide semiconductor laser device, light leakage to the electrode provided on the ridge portion side can be suppressed, and therefore oscillation caused by the electrode on the ridge portion side. It is possible to provide a semiconductor laser device capable of a low power consumption operation capable of reducing the laser beam absorption, reducing the internal loss, increasing the oscillation efficiency and reducing the oscillation threshold current.

  In addition, according to the method for manufacturing a semiconductor laser device of the present invention, it is possible to provide a method capable of manufacturing a semiconductor laser device capable of low threshold current oscillation and high efficiency operation at low cost.

  Further, according to the optical disk apparatus of the present invention, by using the semiconductor laser element of the present invention, it is possible to provide an optical disk apparatus which can be operated at lower cost and with lower power consumption than the conventional optical disk apparatus.

  Further, according to the optical transmission system of the present invention, by using the semiconductor laser element of the present invention for the optical transmission module, it is possible to provide an optical transmission module that can operate with lower power consumption and is less expensive than the conventional one. Therefore, it is possible to reduce the price of the optical transmission system.

  Hereinafter, a semiconductor laser device, a method for manufacturing a semiconductor laser device, an optical disk device, and an optical transmission system according to the present invention will be described in detail with reference to the illustrated embodiments.

[First Embodiment]
FIG. 1 shows the structure of a semiconductor laser device according to the first embodiment of the present invention. In the first embodiment, the first conductivity type is n-type, and the second conductivity type is p-type.

As shown in FIG. 1, the semiconductor laser device includes an n-GaAs buffer layer 102, an n-Al _0.453 Ga _0.547 As first lower cladding layer 103, an n-Al _0.5 Ga _0.5 As layer on an n-GaAs substrate 101. 2 lower cladding layer 104, Al _0.4278 Ga _0.5722 As lower guide layer 105, multiple strain quantum well active layer 106, Al _0.4278 Ga _0.5722 As upper guide layer 107, p-Al _0.4885 Ga as an example of a second conductivity type semiconductor layer _{A 0.5115} As first upper cladding layer 108 and a p-Al _0.4885 Ga _0.5115 As second upper cladding layer 109 as an example of a low-concentration semiconductor layer are sequentially stacked. A p-GaAs etching stop layer 110, a p-Al _0.4885 Ga _0.5115 As third upper cladding layer 111, and a p-GaAs contact layer are formed on the second upper cladding layer 109 so as to form a forward mesas stripe-shaped ridge portion 130. 112 and a p ⁺ -GaAs contact layer 113 as an example of a high-concentration semiconductor layer are provided. Further, the top portion of the ridge portion 130, the side surface portion, and the upper surface of the second upper cladding layer 109 (the portion corresponding to the side of the ridge portion 130 excluding the portion directly below the ridge portion 130) As an example of the electrode, a p-side electrode 114 made of a multilayer metal thin film formed by stacking Au / Ti / Pt / Au in this order is provided. Reference numerals 114a, 114b, and 114c denote portions covering the top and side portions of the ridge portion 130 and the upper surface of the second upper cladding layer 109 (referred to as “electrode portions” as appropriate). The contact resistance between the electrode portion 114a and the top portion (contact layer 113) of the ridge portion 130 has a sufficiently low value. On the other hand, the interface formed between the electrode portion 114c and the second upper clad layer 109 has a function of blocking a downward current in FIG.

  FIG. 2 is an enlarged schematic view of the vicinity of the ridge portion 130 in order to explain the p-side electrode 114. In the p-side electrode 114, the layer made of Au in contact with the semiconductor is called the lowermost layer 114A of the upper electrode, and the layer made of Ti / Pt / Au formed thereon is called the upper layer electrode. In the upper layer electrode provided on Au of the lowermost layer 114A, Ti is the adhesion improving layer 114B, Pt is the diffusion preventing layer 114C, and Au in the uppermost layer is the low resistance layer 114D. Further, a compound layer 115 in which the lowermost layer Au of the upper electrode and each semiconductor layer material are alloyed is formed at the interface between each semiconductor layer in contact with the p-side electrode 114. As shown in FIG. 1, a multilayer metal thin film of AuGe / Ni / Au is formed as an n-side electrode 116 on the back surface of the n-GaAs substrate 101.

The p-AlGaAs first upper cladding layer 108, the p-AlGaAs second upper cladding layer 109, the p-GaAs etching stop layer 110, the p-AlGaAs third upper cladding layer 111, the p-GaAs contact layer 112, and the p ⁺ -GaAs. The contact layer 113 constitutes a second conductivity type semiconductor layer group.

  Next, a method for manufacturing the semiconductor laser element will be described with reference to FIGS. 3A to 3D.

First, as shown in FIG. 3A, an n-GaAs buffer layer 102 (layer thickness: 0.5 μm, Si doping concentration: 8 × 10 ¹⁷ cm ⁻³ ) on an (100) plane n-GaAs substrate 101, n-Al _0.453 Ga _0.547 As first lower cladding layer 103 (layer thickness: 3.0 μm, Si doping concentration: 5 × 10 ¹⁷ cm ⁻³ ), n-Al _0.5 Ga _0.5 As second lower cladding layer 104 (layer thickness) : 0.24 μm, Si doping concentration: 5 × 10 ¹⁷ cm ⁻³ ), Al _0.4278 Ga _0.5722 As lower guide layer 105 (layer thickness 0.1 μm), multiple strain quantum well active layer 106, Al _0.4278 Ga _0.5722 As upper guide Layer 107 (layer thickness: 0.1 μm), p-Al _0.4885 Ga _0.5115 As first upper cladding layer 108 (layer thickness: 0.2 μm, C doping concentration: 1 × 10 ¹⁸ cm ⁻³ ), p-Al _0.4885 Ga _0.5115 As second upper cladding layer 109 (thickness: 0.1 [mu] m, C doping ^{concentration: 1 × 10 17 cm -3)} , p- aAs etching stop layer 110 (thickness 3 nm, C doping ^{concentration: 2 × 10 18 cm -3)} , p-Al 0.4885 Ga 0.5115 As third upper cladding layer 111 (layer thickness 1.28, C doping concentration: 2.7 × 10 ¹⁸ cm ⁻³ ), p-GaAs contact layer 112 (layer thickness: 0.2 μm, C doping concentration: 3.3 × 10 ¹⁸ cm ⁻³ ), p ⁺ -GaAs contact layer 113 (layer thickness: 0.1). 3 μm and C doping concentration: 1 × 10 ²⁰ cm ⁻³ ) are successively grown by MOCVD. The multi-strain quantum well active layer 106 includes an In _0.2655 Ga _0.7345 As _0.5914 P _0.4086 compression strain quantum well layer (strain 0.47%, layer thickness 5 nm, two layers) and an In _0.126 Ga _0.874 As _0.4071 P _0.5929 barrier layer (strain -1.2%, three layers with a layer thickness of 9 nm, 5 nm, and 9 nm from the substrate side, the closest to the substrate being the n-side barrier layer and the farthest being the p-side barrier layer) Yes.

  Next, in FIG. 3A, a resist mask 117 (mask width 3.5 μm) is formed by a photolithography process in a region 118a (see FIG. 1) where a mesa stripe portion to be a ridge portion 130 (shown in FIG. 1) is to be formed. To do. The resist mask 117 is formed so as to extend in a stripe shape in the <0-11> direction corresponding to the stripe direction in which the ridge portion 130 to be formed extends.

  Next, as shown in FIGS. 3B to 3D, a portion 118b (see FIG. 1) corresponding to the side of the resist mask 117 in the semiconductor layers 113, 112, 111, and 110 is removed by etching (etching step). .

Specifically, as shown in FIG. 3B, first, etching is performed by wet (wet) etching from the upper surface side of the p ⁺ -GaAs contact layer 113 in the depth direction to immediately above the p-GaAs etching stop layer 110. . In this example, two steps were performed using a mixed aqueous solution of sulfuric acid and hydrogen peroxide and hydrofluoric acid. By using the fact that the etching rate of GaAs is very slow when hydrofluoric acid is used, the etching surface can be flattened and the width of the mesa stripe can be controlled. Subsequently, while removing the p-GaAs etching stop layer 110 with a mixed aqueous solution of ammonia and hydrogen peroxide, the overhang portions of the GaAs contact layers 112 and 113 are taken. The etching depth at this time is 1.78 μm, and the width of the lowermost portion of the forward mesa stripe is about 3.2 μm. After the etching, the resist mask 117 is removed.

  Subsequently, as shown in FIG. 3C, Au (thickness: 50 nm) as the lowermost layer of the upper electrode and Ti (thickness) as a part of the upper electrode and the adhesion improving layer are formed by using an electron beam evaporation method. : 50 nm), Pt (thickness: 50 nm) as a diffusion prevention layer, and Au (thickness: 400 nm) as a low resistance layer are sequentially laminated to form a p-side electrode (upper electrode) 114. .

  Thereafter, the n-GaAs substrate 101 is ground from the back side to a desired thickness (here, about 100 μm) by lapping, and from the back side by resistance heating vapor deposition, an AuGe alloy (Au: 88%, Ge). : 12%) is laminated to 100 nm, then Ni (thickness: 15 nm) and Au (thickness: 300 nm) are laminated to form the n-side electrode 116 (shown in FIG. 1).

Subsequently, an alloying process for the p-side electrode 114 and the n-side electrode 116 is performed by heating to 400 ° C. for 1 minute in an N ₂ or H ₂ atmosphere. As a result, as shown in FIG. 3D, a compound layer 115 in which Au and each semiconductor layer material are alloyed is formed at the interface between the p-side electrode 114 and each semiconductor layer in contact with the p-side electrode 114. .

  Subsequently, the n-GaAs substrate 101 is divided into bars having a desired resonator length (here, 800 μm), end face coating (not shown) is performed, and further divided into chips (800 μm × 250 μm). The semiconductor laser device according to the first embodiment of the present invention is completed.

  In the first embodiment, a semiconductor laser element for an optical disk device having an oscillation wavelength band of 780 nm is described as an example. However, the present invention is not limited to this, and is used for other oscillation wavelength bands and other applications. Needless to say, the present invention can be applied to a semiconductor laser element.

  FIG. 3E shows the relationship between the refractive index and the metal material for the lowermost layer of the upper electrode used in the present invention. In FIG. 3E, the horizontal axis represents the wavelength (nm) and the vertical axis represents the refractive index. For reference, it is used as the lowermost layer in the conventional example. In the first embodiment, Ti used as the adhesion improving layer and Pt used as the diffusion preventing layer are also shown. As described above, the lowermost layer of the upper electrode is Au in the first embodiment. As can be seen from FIG. 3E, the refractive index of Au for light in the 780 nm band is smaller than 1.0 and is about 0.16.

  On the other hand, in the semiconductor laser device of the first embodiment, the effective refractive index in the vertical direction outside the ridge portion 130 is 3.354. This value is very common in the structure of this type of semiconductor laser device, and is usually about 3.0 to 3.5. Therefore, as described above, the refractive index of Au in the lowermost layer of the upper electrode is sufficiently smaller than the effective refractive index in the vertical direction outside the ridge portion 130.

  As described above, according to the semiconductor laser device and the manufacturing method thereof, the lowermost layer of the upper electrode is formed outside the ridge portion by using a material having a refractive index smaller than 1.0 with respect to the oscillation laser light having a wavelength of 780 nm. Since the oscillation laser beam is strongly confined in the semiconductor layer, the shape of the light distribution is not attracted to the ridge side (upper electrode side). It was. As a result, internal loss due to light absorption of the upper electrode material can be reduced.

FIG. 3F shows, by simulation, the relationship between the film thickness of the lowermost layer and the internal loss of the 0th-order mode when the upper electrode (Ti / Pt / Au) is provided on the lowermost layer (Au) as the upper electrode. If the film thickness of the lowermost layer of the upper electrode is at least 30 nm or more from FIG. 3F, the internal loss can be 1 cm ⁻¹ or less, and the influence of the refractive index of the upper electrode formed on the lowermost layer can be eliminated. . That is, by setting the thickness of the lowermost layer to 30 nm or more, it is possible to freely change the configuration of the upper electrode portion so as to satisfy the requirements related to low resistance and high reliability required for the upper electrode. .

  As can be seen from FIG. 3E, there are Ag, Au, Cu, and Al as materials having a region where the refractive index is 1.0 or less with respect to light having a wavelength of 400 nm to 1550 nm. With reference to FIG. 3E, any one of the above four materials that can have a refractive index of 1.0 or less with respect to a desired oscillation wavelength may be selected.

  Of the above-mentioned Ag, Au, Cu, and Al, Au is formed on GaAs, and then heat can be diffused rapidly and spiked into GaAs by heat treatment or energization, reducing reliability and oscillation efficiency. In the first embodiment, nickel (Ni) is catalytically used at the interface between GaAs and Au (not shown) to suppress such diffusion phenomenon.

  On the Ag (or Au, Cu or Al) which is the lowermost layer of the upper electrode, as an upper layer electrode, an adhesion improving layer for improving adhesion with the lowermost layer material, diffusion of the upper layer material to the lower layer side It is preferable to further form three layers of a diffusion preventing layer for preventing the above and a low resistance layer for reducing the wiring resistance and the contact resistance. With such a configuration, the oscillation laser beam is not absorbed by the electrode, so that the internal loss does not increase, and since the upper layer electrode is provided on the lowermost layer, it has a low electrode resistance and is stable during operation. Thus, it is possible to obtain an upper electrode excellent in reliability that can maintain the electrode state having the low resistance value. When the upper layer electrode is formed in a clean atmosphere without exposing the surface of the lowermost layer of the upper electrode to the atmosphere, the adhesion improving layer is not necessarily required. As the adhesion improving layer, in addition to Ti used in the first embodiment, Cr, Mo, or the like can be used. Further, as shown in the first embodiment, Pt is preferable as the diffusion preventing layer for preventing the diffusion of Au used as the low resistance layer. In addition to Au, Cu, Ag, Al, etc. have good conductivity as the low resistance layer. However, since these metal materials excluding Au are easily oxidized, the low resistance layer serving as the outermost surface of the electrode is used. May not be preferable.

In the semiconductor laser device of the first embodiment, no current blocking layer or insulating film for current confinement is formed at the interface between the upper electrode and the second conductivity type semiconductor layer group. In the region excluding the uppermost portion, current confinement is performed by forming a Schottky junction at the interface between the electrode and the semiconductor layer. The p-side electrode 114 made of Au / Ti / Pt / Au forms a compound layer 115 (shown in FIG. 3D) alloyed with a GaAs-based semiconductor material by performing heat treatment at 350 to 450 ° C. The compound layer 115 forms a good ohmic junction or a stable Schottky junction with the p-type semiconductor layer according to the doping concentration of the p-type semiconductor layer. By utilizing this, in the semiconductor laser device of the first embodiment, the p ⁺ -GaAs contact layer as an example of the high concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more in the mesa stripe portion 118a. A compound layer on the high-concentration side of Au and GaAs that realizes a good ohmic junction is formed at the interface between the p-side electrode 114 and the p-side electrode 114, and 1 × 10 ¹⁷ cm ⁻³ or less in the mesa stripe outer region 118 b As an example of a low-concentration semiconductor layer having a doping concentration, p-Al _0.4885 Ga _0.5115 As As the low concentration side of Au and AlGaAs exhibiting a stable Schottky junction at the interface between the second upper cladding layer 109 and the p-side electrode 114 The compound layer is formed. When the heat treatment is performed at a temperature lower than 350 ° C. or higher than 450 ° C., good ohmic bonding cannot be obtained, and Schottky bonding properties are also deteriorated. In the first embodiment, a heat treatment step at 400 ° C. for 1 minute is added in consideration of the optimum conditions for the alloying treatment of AuGe / Ni / Au as the n-side electrode.

Furthermore, a first upper cladding layer 108 having a doping concentration higher than that of the second upper cladding layer 109 is provided between the second upper cladding layer 109 and the multiple strain quantum well active layer 106, and the first upper cladding layer By optimizing the layer thicknesses of the layer 108 and the second upper cladding layer 109, the increase in device resistance more than necessary has been successfully suppressed. The layer thickness of the second upper cladding layer 109 is set to be larger than the thickness of the compound layer 115. In the present invention, the thickness of the compound layer 115 is 50 nm (0.05 μm) while the thickness of the second upper cladding layer 109 is 0.1 μm. In order to perform sufficient current confinement, a semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less is required immediately below the compound layer 115. Considering element resistance, it is not preferable that a low doping concentration layer is present immediately below the ridge portion. Therefore, the compound layer 115 is preferably not so thick. According to the study by the inventors, the thickness of the semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less is preferably about 0.3 μm or less at maximum. Further, the thickness of the compound layer 115 may be 0.2 μm at the maximum, and if it is more than that, the effect of increasing the device resistance due to the increase in the thickness of the semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less increases. End up.

  As a result, the semiconductor laser device according to the first embodiment realizes a good element resistance without performing the crystal regrowth process of the electrode contact layer, and adds an embedded regrowth process of the current block layer. Without making it possible to perform sufficient current confinement.

Further, the semiconductor laser device of the first embodiment has a high degree of freedom in optical design. The degree of freedom in optical design is that the clad layer formed on the upper side of the active layer is divided into a plurality of parts, and the second upper clad layer 109 mainly responsible for current confinement by Schottky junction, and mainly the optical characteristics. This is because the first upper cladding layer 108 used for adjustment is separated. The doping concentration of the second upper cladding layer 109 as the second conductivity type semiconductor layer mainly responsible for current confinement due to Schottky junction is 1 × 10 ¹⁷ cm ⁻³ or less and the thickness is as large as possible within the range thicker than the compound layer 115. By making the layer thickness thin, the increase in element resistance due to the addition of a layer of 1 × 10 ¹⁷ cm ⁻³ or less is kept to a minimum.

  By adopting such a configuration, the first upper cladding layer 108 can be freely changed in layer thickness, composition, etc. according to the required optical characteristic specifications without being subjected to any restrictions in consideration of Schottky bonding properties. Can now.

  In the semiconductor laser device of the first embodiment, the wavelength is 780 nm, but the present invention is not limited to this. For example, the present invention can also be applied to an InGaAlP / GaAs semiconductor laser element having a wavelength of 650 nm and an InGaN / GaN semiconductor laser element having a wavelength of 405 nm. In that case, an optimal metal material may be selected with reference to FIG. 3E as the lowermost layer of the upper electrode.

  Further, a semiconductor layer similar to an interface protective layer that is not explicitly shown in the first embodiment may be provided at an interface between semiconductor layers having different material systems. In the first embodiment, the wet etching method is used for forming the structure of the ridge portion. Of course, a dry etching method may be used. Further, the ridge portion may be formed by combining dry etching and wet etching.

In the first embodiment, an ohmic junction is formed at the interface between the p ⁺ -GaAs contact layer 113 and the p-side electrode 114, and a Schottky junction is formed at the interface between the p-AlGaAs second upper cladding layer 109 and the p-side electrode 114. However, the Schottky junction may be formed between at least a part of the region other than the uppermost portion of the ridge portion and the upper electrode.

[Second Embodiment]
FIG. 4 shows the structure of an optical disc device 200 according to the second embodiment of the present invention. The optical disc apparatus 200 is for writing data on the optical disc 201 and reproducing the written data. As the light emitting element used at that time, the optical disc device 200 of the first embodiment of the present invention described above is used. A semiconductor laser element 202 is provided.

  The optical disk device 200 will be described in more detail. At the time of writing, the signal light emitted from the semiconductor laser element 202 is converted into parallel light by the collimator lens 203, passes through the beam splitter 204, the polarization state is adjusted by the λ / 4 polarizing plate 205, and then the objective lens 206. Is condensed and irradiated onto the optical disc 201. At the time of reading, the optical disc 201 is irradiated with a laser beam not carrying a data signal along the same path as at the time of writing. This laser beam is reflected on the surface of the optical disc 201 on which data is recorded, passes through the laser beam irradiation objective lens 206, the λ / 4 polarizing plate 205, and then is reflected by the beam splitter 204 to change the angle by 90 °. The light is condensed by the light receiving element objective lens 207 and is incident on the signal detecting light receiving element 208. Then, the recorded data signal is converted into an electric signal by the intensity of the laser beam incident in the signal detecting light receiving element 208 and is reproduced by the signal light reproducing circuit 209 to the original signal.

  The optical disk device of the second embodiment uses a semiconductor laser element that can operate at low threshold current oscillation and high efficiency with lower internal loss than the conventional one, and can be manufactured at low cost. A possible optical disk apparatus can be provided at a low price.

  Here, an example in which the semiconductor laser device 202 of the first embodiment is applied to a recording / reproducing optical disk device has been described. However, an optical disk reproducing device, an optical disk recording device, and other wavelength bands using the same wavelength 780 nm band (for example, Needless to say, the present invention can also be applied to an optical disc apparatus of a 650 nm band).

[Third Embodiment]
FIG. 5A is a cross-sectional view showing an optical transmission module 300 used in the optical transmission system of the third embodiment of the present invention. FIG. 5B is an enlarged perspective view of the light source portion in the light transmission module 300. In the third embodiment, an InGaAs semiconductor laser element (laser chip 301) having an oscillation wavelength of 890 nm using the configuration and manufacturing method described in the first embodiment as a light source and silicon (Si) as a light receiving element 302 are used. A pin photodiode is used. As will be described in detail later, by providing the same optical transmission module 300 on both sides (for example, a terminal and a server) that perform communication, an optical transmission system that transmits and receives an optical signal between both optical transmission modules 300 is configured. The

  In FIG. 5A, a positive and negative electrode pattern for driving a semiconductor laser element is formed on a circuit board 306. As shown in the drawing, a recess 306a having a depth of 300 μm is provided in a portion where a laser chip is mounted. . The laser mount 310 on which the laser chip 301 is mounted is fixed to the recess 306a with solder. A flat portion 313 (shown in FIG. 5B) of the positive electrode 312 of the laser mount 310 is electrically connected to a laser driving positive electrode portion (not shown) on the circuit board 306 by a wire 307a. The recess 306a has a depth that does not hinder the emission of laser light, and the roughness of the surface does not affect the emission angle.

  The light receiving element 302 is also mounted on the circuit board 306, and an electric signal is taken out by the wire 307b. In addition, a laser driving / reception signal processing IC circuit 308 is mounted on the circuit board 306.

  Next, an appropriate amount of liquid silicon resin 309 is dropped onto a portion where the laser mount 310 fixed to the recess 306a is mounted using solder. In the silicon resin 309, a filler that diffuses light is mixed. The silicon resin 309 stays in the recess 306a due to surface tension, covers the laser mount 310, and is fixed to the recess 306a. In this third embodiment, the recess 306a is provided on the circuit board 306 and the laser mount 310 is mounted. However, as described above, the silicon resin 309 stays on the surface of the laser chip 301 and its vicinity because of surface tension. The recess 306a is not necessarily provided.

  Then, it is heated at 80 ° C. for about 5 minutes to be cured until the silicon resin 309 becomes jelly-like. Next, it is covered with a transparent epoxy resin mold 303. Above the laser chip 301, a lens part 304 for controlling the emission angle is formed, and above the light receiving element 302, a lens part 305 for condensing the signal light is integrally formed as a molded lens.

  Next, the laser mount 310 will be described with reference to FIG. 5B. As shown in FIG. 5B, a laser chip 301 is die-bonded to an L-shaped heat sink 311 using an indium (In) glue material or the like. The laser chip 301 is an InGaAs-based semiconductor laser element having the configuration described in the first embodiment. The laser chip lower surface 301b is coated with a high reflection film, while the laser chip upper surface 301a is coated with a low reflection film. Is coated. These reflective films also serve as protection for the end face of the laser chip.

  A positive electrode 312 is fixed to the base 311 b of the heat sink 311 with an insulator so as not to be electrically connected to the heat sink 311. The positive electrode 312 and the p electrode 301c on the surface of the laser chip 301 are connected by a gold wire 307c. As described above, the laser mount 310 is fixed to the negative electrode (not shown) of the circuit board 306 of FIG. 5A with solder, and the flat part 313 on the upper side of the positive electrode 312 and the positive electrode part ( And a wire 307a. By forming such wiring, the optical transmission module 300 that can obtain the laser beam 314 by oscillation is completed.

  Since the optical transmission module 300 of the third embodiment uses the single growth type semiconductor laser device that can be manufactured at a low cost as described above, the unit price of the module can be significantly reduced as compared with the conventional one. Further, since the semiconductor laser element capable of operating with high efficiency and low threshold current is used, the power consumption of the optical transmission module 300 can be reduced.

  As described above, by providing the same optical transmission module 300 on both sides that perform communication, an optical transmission system that transmits and receives optical signals between both optical transmission modules 300 is configured.

  FIG. 6 shows a configuration example of an optical transmission system using the optical transmission module 300. In this optical transmission system, the base station 315 installed on the ceiling of the room includes the optical transmission module 300, and the personal computer 316 includes the same optical transmission module as described above (denoted by reference numeral 300 'for distinction). Yes. An optical signal emitted with information from the light source of the optical transmission module 300 ′ on the personal computer 316 side is received by the light receiving element of the optical transmission module 300 on the base station 315 side. An optical signal emitted from the light source of the optical transmission module 300 on the base station 315 side is received by the light receiving element of the optical transmission module 300 ′ on the personal computer 316 side. In this way, data communication using light (infrared rays) can be realized.

  As described above, the optical transmission module 300 of the third embodiment uses a semiconductor laser element that can be manufactured at a low cost and has a lower internal loss than the conventional one. Therefore, an optical transmission system with low cost and low power consumption can be obtained. It becomes possible to provide. When this optical transmission system is installed in a portable device, the continuous operation time can be extended compared to the case where a conventional light emitting device is installed due to low power consumption, and a more convenient portable optical transmission system is constructed at a low cost. It becomes possible to do.

  The semiconductor laser device, the optical disk device, and the optical transmission system of the present invention are not limited to the above-described embodiments. For example, the thickness of the well layers and barrier layers constituting the multi-strain quantum well active layer 106 are It goes without saying that various changes such as the number of layers can be made without departing from the scope of the present invention.

FIG. 1 is a schematic sectional view of a semiconductor laser device according to a first embodiment of the present invention. FIG. 2 is an enlarged schematic view of the p-side electrode in the vicinity of the ridge portion of the semiconductor laser element. FIG. 3A is a schematic cross-sectional view illustrating the manufacturing process of the semiconductor laser element. FIG. 3B is a schematic cross-sectional view illustrating the manufacturing process of the semiconductor laser element following FIG. 3A. FIG. 3C is a schematic cross-sectional view for explaining the manufacturing process of the semiconductor laser element, following FIG. 3B. FIG. 3D is a schematic cross-sectional view for explaining the manufacturing process of the semiconductor laser element, following FIG. 3C. FIG. 3E is a graph showing the refractive index of the metal material with respect to the wavelength. FIG. 3F is a graph showing the relationship between the thickness of the lowermost layer of the upper electrode and the internal loss. FIG. 4 is a schematic diagram for explaining an optical disc apparatus according to the second embodiment of the present invention. FIG. 5A is a schematic diagram for explaining an optical transmission module according to a third embodiment of the present invention. FIG. 5B is a schematic diagram for explaining the optical transmission module. FIG. 6 is a schematic diagram illustrating an optical transmission system using the optical transmission module. FIG. 7 is a schematic cross-sectional view illustrating a conventional semiconductor laser element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... n-GaAs substrate 102 ... n-GaAs buffer layer 103 ... n-AlGaAs first lower cladding layer 104 ... n-AlGaAs second lower cladding layer 105 ... AlGaAs lower guide layer 106 ... Multiple strain quantum well active layer 107 ... AlGaAs Upper guide layer 108 ... p-AlGaAs first upper cladding layer 109 ... p-AlGaAs second upper cladding layer 110 ... p-GaAs etching stop layer 111 ... p-AlGaAs third upper cladding layer 112 ... p-GaAs contact layer 113 ... p ⁺ -GaAs contact layer 114... p-side electrode 114A... bottom layer 114B... adhesion improving layer 114C .. diffusion prevention layer 114D .. low resistance layer 115 ... compound layer 116 ... n-side electrode 117 ... resist mask 118a ... mesa stripe portion 118b ... Mesa stripe outer region 130 ... Ridge portion 200 ... Optical disc device 201 ... Optical disc 2 DESCRIPTION OF SYMBOLS 02 ... Semiconductor laser element 203 ... Collimating lens 204 ... Beam splitter 205 ... (lambda) / 4 polarizing plate 206 ... Objective lens 207 ... Light receiving element objective lens 208 ... Signal detection light receiving element 209 ... Signal light reproduction circuit 300,300 '... Light Transmission module 301 ... Laser chip 301a ... Laser chip upper surface 301b ... Laser chip lower surface 301c ... P electrode 302 ... Light receiving element 303 ... Epoxy resin mold 304 ... Lens portion 305 ... Lens portion 306 ... Circuit substrate 306a ... Recesses 307a, 307b, 307c ... Wire 308 ... Laser drive / received signal processing IC circuit 309 ... Silicon resin 310 ... Laser mount 311 ... Heat sink 311b ... Base 312 ... Positive electrode 313 ... Flat part 314 ... Laser beam 315 ... Base station 316 ... Personal computer 401 ... n -GaAs substrate 402 ... n-InGaP cladding layer 403 ... strain quantum well active layer 404 ... p-InGaP cladding layer 405 ... p-InGaAs contact layer 406 ... p electrode 407 ... n electrode 408 ... Schottky junction

Claims (12)

On the first conductivity type substrate, at least an active layer and a second conductivity type semiconductor layer group are provided, and a part of the upper side of the second conductivity type semiconductor layer group forms a striped ridge portion. A ridge waveguide semiconductor laser element,
The ridge formed on the second conductivity type semiconductor layer group and on the side surface of the ridge portion of the second conductivity type semiconductor layer group or in the region of the second conductivity type semiconductor layer group excluding the ridge portion. A multi-layered upper electrode in contact with at least one of the surfaces in the vicinity of the part,
A semiconductor laser device having a refractive index with respect to an oscillation laser beam of 1.0 or less in at least a lowermost layer of the upper electrode. The semiconductor laser device according to claim 1,
A semiconductor laser element, wherein a refractive index with respect to the oscillation laser beam is 1.0 or less, and a film thickness of a lowermost layer of the upper electrode is 30 nm or more. The semiconductor laser device according to claim 1,
A semiconductor laser element, wherein the lowermost layer of the upper electrode is made of at least one of Au, Ag, Cu, or Al. The semiconductor laser device according to claim 1,
A semiconductor laser device, wherein at least three layers of an adhesion improving layer, a diffusion prevention layer, and a low resistance layer are sequentially laminated on the lowermost layer of the upper electrode. The semiconductor laser device according to claim 1,
The uppermost portion of the ridge portion of the second conductivity type semiconductor layer group and the upper electrode form an ohmic junction, and at least a part of the region other than the uppermost portion of the ridge portion and the upper electrode are A semiconductor laser element characterized in that a Schottky junction is formed. The semiconductor laser device according to claim 1,
The uppermost part of the ridge portion of the second conductivity type semiconductor layer group is a high concentration semiconductor layer having a second conductivity type doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more,
At least part of the region other than the uppermost portion of the ridge portion of the second conductivity type semiconductor layer group is a low concentration semiconductor layer having a second conductivity type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less,
At the interface between the upper electrode and the high-concentration semiconductor layer, a high-concentration compound layer composed of the constituent elements of the upper electrode and the constituent elements of the high-concentration semiconductor layer is formed
A semiconductor laser element, wherein a compound layer on a low concentration side composed of a material of the upper electrode and constituent elements of the low concentration semiconductor layer is formed at an interface between the upper electrode and the low concentration semiconductor layer. The semiconductor laser device according to claim 6, wherein
A semiconductor laser element, wherein a second conductivity type semiconductor layer having a doping concentration of at least 1 × 10 ¹⁷ cm ⁻³ or more is formed between the low-concentration semiconductor layer and the active layer. Forming an active layer on a substrate of a first conductivity type;
Forming a second conductivity type semiconductor layer group on the active layer;
Removing a part of the second conductivity type semiconductor layer group to form a ridge portion;
Forming a top electrode on the second conductivity type semiconductor layer group using a metal material having a refractive index with respect to the oscillation laser light of 1.0 or less as a lowermost layer. Manufacturing method. In the manufacturing method of the semiconductor laser device according to claim 8,
In the step of forming the second conductivity type semiconductor layer group, a high concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more is formed as an uppermost portion of the ridge portion, and at least in a region other than the ridge portion. Forming a low-concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less,
A method of manufacturing a semiconductor laser device comprising a step of forming a compound layer at an interface between the second conductive type semiconductor layer group and the upper electrode by performing a heat treatment after the step of forming the upper electrode. . In the manufacturing method of the semiconductor laser device according to claim 9,
In the step of forming the second conductivity type semiconductor layer group, a second conductivity type semiconductor layer having a doping concentration of at least 1 × 10 ¹⁷ cm ⁻³ or more between the low concentration semiconductor layer and the active layer. Forming a semiconductor laser element.   8. An optical disc apparatus using the semiconductor laser element according to claim 1. 8. An optical transmission system using the semiconductor laser device according to claim 1.

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