JP2006059975A - Semiconductor laser element, manufacturing method therefor, optical disk device, and optical transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser element and a manufacturing method therefor which laser element is adapted to prevent oscillation laser beams from leaking out to an electrode formed above an active layer to offer high oscillation efficiency, to enable low power consumption (low threshold current) operation, and to reduce manufacturing costs. <P>SOLUTION: Semiconductor layers including an uppermost active layer 106 are formed on a first conductive board 101, which is followed by the formation of a group of second conductive semiconductor layers 107 to 114 including low-concentration semiconductor layers 110, 111 having a doping concentration of 1×10<SP>17</SP>cm<SP>-3</SP>or lower and a high-concentration semiconductor layer 114 having a doping concentration of 5×10<SP>18</SP>cm<SP>-3</SP>or higher. Then, a part of the second conductive semiconductor layer group, the layers 112 to 114, are eliminated to expose the low-concentration semiconductor layers to form a ridge portion 130 having the high-concentration semiconductor layer 114 on the top thereof. The ridge is then coated with an electrode 115 containing an Al layer 115a in such a way that the Al layer is in contact with the ridge upper face and with at least either of the ridge side faces and the exposed surface of the low-concentration semiconductor layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser element and a manufacturing method thereof, and typically relates to a semiconductor laser element suitably used for an optical transmission device, an optical transmission module portion of an optical transmission system, and the like and a manufacturing method thereof.

  The present invention also relates to an optical disc apparatus and an optical transmission system provided with such a semiconductor laser element.

  Semiconductor laser elements are widely used in optical disk devices and optical transmission systems. Among them, a semiconductor laser element called a ridge embedded type is known as a semiconductor laser element having high reliability and capable of operating with low power consumption (low threshold current). However, in the manufacturing process of the ridge buried type semiconductor laser device, in addition to the first crystal growth step performed for forming the semiconductor layer including the active layer and the cladding layer, the second time for forming the current confinement layer. And a third crystal growth step for forming a contact layer, and further, it must be manufactured through a complicated process. For this reason, there are problems in that the yield is poor and the manufacturing cost is high.

  Therefore, as a conventional semiconductor laser element that can be manufactured more easily and at low cost, there is a ridge waveguide type semiconductor laser element that has a ridge portion on an active layer and can be manufactured by a single crystal growth process (for example, Patent Documents). 1 (see JP-A-4-111375).

  FIG. 11 is a schematic cross-sectional view of this conventional semiconductor laser device. This conventional semiconductor laser device is manufactured as follows.

  First, an n-type InGaP cladding layer 402, an InGaAs / GaAs strained quantum well active layer 403, a p-type InGaP cladding layer 404, and a p-type InGaAs contact layer are formed on an n-type GaAs substrate 401 by MOCVD (metal organic chemical vapor deposition). 405 are sequentially stacked and etched halfway through the p-type InGaP clad layer 404 by a technique such as photolithography to form a mesa to be a ridge portion, and then Ti / Pt / Au is used as the p electrode 406 and n electrode 407 is used. As a result, Au-Ge-Ni / Au is sequentially deposited.

  When a current is passed through the device thus manufactured, a Schottky junction 408 is formed between the p-type InGaP cladding layer 404 and the p-electrode 406, and between the p-electrode 406 and the p-type InGaAs contact layer 405. Only current flows and current constriction is performed.

  As described above, the ridge-embedded semiconductor laser element requires a total of three crystal growth steps and a complicated manufacturing process. However, in this conventional semiconductor laser element, only one crystal growth step is required. . In addition, this conventional semiconductor laser device realizes current confinement using a Schottky junction, not a configuration using an inorganic insulating film for current confinement, which is generally called an air ridge type, among ridge waveguide semiconductor laser devices. Due to the configuration, the structure is further simpler and can be manufactured at an overwhelmingly low cost.

  However, it has been found that the conventional semiconductor laser element disclosed in Patent Document 1 described above has the following problems. That is, unlike the above-described ridge-embedded semiconductor laser element and air ridge type ridge waveguide semiconductor laser element, the conventional semiconductor laser element disclosed in Patent Document 1 has a side surface of the ridge portion and an outer side from the ridge portion. The electrode is in direct contact with the surface of the cladding layer extending to the surface. At this time, depending on the refractive index of the semiconductor material constituting the semiconductor laser element and the refractive index of the metal material constituting the electrode, the distribution of the oscillated laser beam was formed on the side surface of the ridge portion and the surface of the cladding layer near the ridge portion. The shape may easily leak to the electrode side.

  The refractive index of the electrode material on the ridge side used in the conventional semiconductor laser element disclosed in Patent Document 1 is about 3.0 to 3.6 when Ti in contact with the semiconductor layer is in the wavelength range of 650 nm to 1.5 μm. Pt provided on the upper side of Ti is 2.9 to 5.5 in the same wavelength range of 668 nm to 1.5 μm. On the other hand, the effective refractive index in the vertical direction outside the ridge portion is also about 3.2, for example, and the refractive indexes of Ti and Pt cannot be ignored.

  Thus, if the effective refractive index in the vertical direction outside the ridge is close to the refractive index of the electrode material directly formed on the semiconductor layer, the laser light oscillated in the electrode direction may easily leak. there were.

  In the ridge buried semiconductor laser device described above, there is a buried layer made of a semiconductor material and provided for current confinement on the p-type cladding layer excluding the ridge portion, and further on the ridge portion and the p-type cladding layer, Such a problem was not observed because a semiconductor layer to be a contact layer was formed. In the air ridge type ridge waveguide semiconductor laser element, electrodes are formed on the inorganic insulating film provided for current confinement on the side surface of the ridge portion and the surface of the cladding layer extending outward from the ridge portion. Therefore, such a problem did not need to be considered.

However, in the conventional semiconductor laser device disclosed in Patent Document 1 described above, light may leak to the electrode formed on the ridge side. In such a case, generally, the metal material constituting the electrode is smaller than the semiconductor material. Since the light absorption coefficient is as high as about 10 ⁴ to 10 ⁵ times, the metal material constituting the electrode becomes a very large absorption component of light, and the internal loss is greatly increased. As a result, it has been found that the above-described conventional semiconductor laser device has problems that the slope efficiency decreases and the oscillation threshold current value increases.
Japanese Patent Laid-Open No. 4-111375 (page 3, FIG. 1)

  Therefore, the object of the present invention is to prevent the oscillation laser light from leaking to the electrode provided above the active layer, thereby enabling high oscillation efficiency and low power consumption (low threshold current) operation. Furthermore, another object of the present invention is to provide a semiconductor laser device that can reduce the manufacturing cost even if it has a ridge structure, and a manufacturing method thereof.

  Another object of the present invention is to provide an optical disc apparatus and an optical transmission system using the semiconductor laser element.

In order to solve the above problems, a semiconductor laser device according to the present invention includes at least an active layer, a second conductivity type semiconductor layer group, and a second conductivity type semiconductor layer group on a first conductivity type substrate. In the semiconductor laser device having the electrode formed thereon, the second conductivity type doping concentration of the first semiconductor layer in contact with the electrode in the second conductivity type semiconductor layer group is 5 × 10 ¹⁸ cm ^{−. 3} or more, and the electrode includes at least an Al layer in contact with the first semiconductor layer.

  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.

  Further, throughout this specification, “upper” means a direction away from the substrate, and “lower” means a direction closer to the substrate. Crystal growth proceeds from “down” to “up”.

  In the semiconductor laser device of the present invention, an ohmic junction capable of obtaining a low contact resistance is formed between the first semiconductor layer and the electrode depending on the doping concentration of the first semiconductor layer.

  In addition, it is desirable that another electrode that forms an ohmic junction with this surface is provided on the surface of the first conductivity type substrate opposite to the surface on which the above layers are laminated. As a result, energization is easily performed between the two electrodes through the active layer, and laser oscillation is realized.

  At this time, Al used for the electrode has a refractive index that is generally sufficiently smaller than the refractive index of the semiconductor material used for the semiconductor layer group, and is approximately 2 or less in the practical wavelength range of the semiconductor laser device. Therefore, the oscillated laser light can be confined in the semiconductor layer without leaking to the electrodes. As a result, there is provided a semiconductor laser device capable of low power consumption operation having a low oscillation threshold current and a high slope efficiency without causing the electrode material to be an absorption component of the oscillation laser light and thus increasing the internal loss. It becomes possible to do.

  In one embodiment, the semiconductor laser device is a ridge waveguide semiconductor laser device in which a part of the upper side of the second conductivity type semiconductor layer group forms a striped ridge portion, The semiconductor layer constitutes the uppermost portion of the ridge portion, and the electrode has the Al layer formed on the upper surface of the uppermost portion of the ridge portion, the side surface of the ridge portion, or the second conductivity type. The semiconductor layer group is formed so as to be in contact with at least one of the surfaces in the vicinity of the ridge portion in the region excluding the ridge portion.

  Similar to the semiconductor laser element disclosed in Patent Document 1, this semiconductor laser element can complete the crystal growth process in the manufacturing stage once. Therefore, although the ridge structure is provided, the manufacturing process is significantly reduced and the manufacturing cost is low as compared with a semiconductor laser device having a general ridge embedded structure.

  In one embodiment, the uppermost portion of the ridge portion and the electrode form an ohmic junction, and the side surface of the ridge portion or the region of the second conductivity type semiconductor layer group excluding the ridge portion is formed. The at least one of the surfaces in the vicinity of the ridge portion and the electrode form a Schottky junction.

  In this embodiment, current confinement is realized by the Schottky junction.

  In one embodiment, the Al layer has a thickness of 30 nm or more.

  According to the semiconductor laser device of the above embodiment, the thickness of the electrode made of Al is set to 30 nm or more, and details will be described later using data, but the effect of using Al having a lower refractive index than the semiconductor material as the electrode. Is maximized. As a result, an increase in internal loss due to the electrode material provided on the ridge portion side can be minimized.

  In one embodiment of the semiconductor laser device, the electrode has a structure in which one or more metal thin films are further stacked on the Al layer.

  According to the semiconductor laser device of the above embodiment, the structure of the electrode is a laminated structure composed of a plurality of metal thin films with Al as the lowermost layer, so that an Al surface that is highly oxidizable can be prevented from being exposed. Therefore, the increase in resistance of the electrode due to the oxidation of Al can be avoided.

  In one embodiment, the electrode is composed of at least three layers, and is located between the lowermost Al layer and the uppermost metal thin film layer, and immediately above the Al layer. A diffusion preventing layer for preventing the material of the uppermost metal thin film layer from diffusing up to the Al layer is formed.

  In this specification, unless otherwise specified, a diffusion prevention layer means that a material formed above that layer (diffusion prevention layer) diffuses to a layer below that layer (diffusion prevention layer). It refers to a material layer provided to prevent this.

  According to the semiconductor laser device of the above-described embodiment, a plurality of stacked metal thin films diffuses to the Al layer that is the lowermost layer of the electrode, thereby changing the electrical and optical characteristics of the Al that is the lowermost layer of the electrode. Can be prevented. As a result, it becomes easy to form an electrode configuration as designed, and a semiconductor laser element that is stable in terms of reliability can be obtained.

  In the semiconductor laser device of one embodiment, the uppermost layer provided on the diffusion prevention layer of the electrode is an Au layer.

  According to the semiconductor laser device of the above embodiment, since the Au layer used as the uppermost layer of the electrode has a low resistance and there is no problem of oxidation, the device resistance can be reduced while facilitating wire bonding or the like by pressure contact. effective.

  When the uppermost layer of the electrode is an Au layer, the diffusion prevention layer is preferably made of Pt.

  According to the semiconductor laser device of the above embodiment, since Pt acts as a good diffusion prevention layer for Au, the uppermost Au layer of the electrode is not in direct contact with the lowermost Al layer, and has a very high resistance. An AlAu alloy layer is not formed in the electrode. From this, it is possible to provide a configuration that does not deteriorate the resistance of the electrode of the semiconductor laser element.

  If the thickness of the diffusion preventing layer made of Pt is 5 nm or more, it is possible to reliably prevent the uppermost electrode layer Au from diffusing up to the Al layer to form an AlAu alloy layer.

  As the diffusion preventing layer, platinum group elements (ruthenium, osmium, rhodium, iridium, palladium) other than Pt, nickel, titanium, molybdenum and the like can be used.

In one embodiment of the semiconductor laser device (ridge waveguide semiconductor laser device), the second conductivity type semiconductor layer group includes a second conductivity type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less. The surface of the second conductivity type semiconductor layer group excluding the ridge portion in the vicinity of the ridge portion is a surface of the second semiconductor layer, and the electrode is the outermost surface of the ridge portion. The upper surface of the first semiconductor layer constituting the upper portion, the side surface of the ridge portion, and the surface of the second semiconductor layer are continuously formed.

According to the semiconductor laser device of the above embodiment, the first semiconductor layer (high height) provided at the top of the ridge structure has a doping concentration of 5 × 10 ¹⁸ cm ⁻³ or more, preferably 1 × 10 ¹⁹ cm ⁻³ or more. In the ohmic junction between the concentration semiconductor layer) and the electrode, a low contact resistance can be obtained.

On the other hand, in a Schottky junction between a second semiconductor layer (low concentration semiconductor layer) having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less provided in a region other than the uppermost portion of the ridge structure and a good current confinement Can be realized. The current confinement property can be further improved as the doping concentration of the second semiconductor layer is decreased from 1 × 10 ¹⁷ cm ⁻³ within the range in which the conductivity type is not reversed. However, the lower limit of the doping concentration of the second conductivity type is about 1 × 10 ¹⁶ cm ⁻³ due to restrictions on crystal growth technology (problem of background impurities).

  Since both good ohmic junction and Schottky junction can be achieved in this way, the crystal regrowth process of the buried layer (current block layer) for current confinement and the crystal regrowth of the contact layer for low contact resistance are achieved. Even without a separate growth step, sufficient current confinement and low contact resistance can be realized, and thermal and electrical reliability can be improved.

In one embodiment of the semiconductor laser device, the second conductivity type having a doping concentration greater than 1 × 10 ¹⁷ cm ⁻³ between the second semiconductor layer (low concentration semiconductor layer) and the active layer. A third semiconductor layer is formed.

  According to the semiconductor laser device of the above embodiment, the third semiconductor layer can be used to change the layer thickness, composition, etc. according to the optical property specifications required for the device without being restricted in consideration of the Schottky junction characteristics. Can be performed freely. In addition, since the third semiconductor layer is doped at a higher concentration than the second semiconductor layer (low-concentration semiconductor layer), an increase in element resistance can be suppressed. The power consumption can be further reduced as compared with the case where it is not provided.

The method of manufacturing a semiconductor laser device according to the present invention includes a step of forming at least an active layer on a first conductivity type substrate, and a doping concentration of 5 × 10 ¹⁸ cm ⁻³ or more on the active layer. A step of forming a second conductivity type semiconductor layer group including a first semiconductor layer of two conductivity types so that a surface of the first semiconductor layer is exposed; and an electrode including an Al layer; Forming on the first semiconductor layer so as to be in contact with the surface of the first semiconductor layer.

  By using this manufacturing method, the above-described semiconductor laser device of the present invention can be realized.

In one embodiment, the second conductivity type semiconductor layer group further includes a second semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less, and the manufacturing method includes the second conductivity type semiconductor layer group. And removing the part of the second conductive type semiconductor layer group until the second semiconductor layer is exposed between the step of forming the electrode and the step of forming the electrode. A step of forming a ridge portion on the uppermost portion, wherein the Al layer is in contact with the upper surface of the ridge portion and at least one of the side surface of the ridge portion or the exposed surface of the second semiconductor layer. Is formed.

  According to the method of manufacturing a semiconductor laser device having the above configuration, an ohmic junction is formed between the first semiconductor layer and the electrode of the ridge portion, and a Schottky junction is formed between the second semiconductor layer and the electrode. It is formed.

  When this manufacturing method is used, the crystal growth process can be completed once, as in the method of manufacturing the semiconductor laser device of Patent Document 1. Therefore, although the ridge structure is provided, the number of steps can be greatly reduced as compared with the manufacturing of a general semiconductor laser device having a buried ridge structure, and the manufacturing cost of the semiconductor laser device can be reduced. That is, according to this embodiment, there is provided a method capable of manufacturing a semiconductor laser element capable of oscillating with a low threshold current without increasing internal loss at low cost.

  In one embodiment, in the step of forming the electrode, an Au film is formed after forming a diffusion prevention layer on the Al layer.

  In this embodiment, an electrode in which low resistance and non-oxidized Au is laminated is formed on Al in contact with the semiconductor layer via a diffusion prevention layer, so that the electrode resistance of the semiconductor laser element is kept low. be able to. At this time, since the diffusion preventing layer is inserted between Al and Au, an AlAu alloy layer is not formed in the electrode, and a lower resistance electrode can be formed.

  Moreover, the manufacturing method of the semiconductor laser element of one Embodiment performs the said electrode formation process, without exposing in the air on the way.

According to the method for manufacturing a semiconductor laser device of the above embodiment, when the electrode is formed, the Al deposition step to the Au deposition step is performed without being exposed to the atmosphere, so that in an atmosphere containing oxygen. Can coat the Al film with a diffusion prevention layer made of Pt or the like and an Au film without oxidizing the surface of Al which is very easily and rapidly oxidized. When the surface of the Al film is oxidized, the adhesion with the diffusion prevention layer which is an upper layer thereof is remarkably lowered, and an extremely high resistance aluminum oxide (Al ₂ O ₃ ) layer is formed at the interface with the diffusion prevention layer. According to the manufacturing method of the above-described embodiment, it is possible to prevent peeling of the stacked electrodes and increase in resistance caused by them.

Also, in one embodiment of the method for manufacturing a semiconductor laser device, in the step of forming the second conductive type semiconductor layer group, the first semiconductor layer (low-concentration semiconductor layer) and the active layer have a 1 A third semiconductor layer of the second conductivity type having a doping concentration greater than × 10 ¹⁷ cm ⁻³ is formed.

  According to the manufacturing method of the semiconductor laser device of the above embodiment, the second conductivity type third semiconductor layer can meet the optical property specification required for the device without being restricted in consideration of the Schottky junction characteristics. Thus, there is provided a method for manufacturing a semiconductor laser device, which can freely change the layer thickness, composition, etc., can suppress an increase in device resistance, and can achieve further reduction in power consumption.

  An optical disc apparatus according to the present invention includes any one of the above semiconductor laser elements.

  According to the above optical disk apparatus, it is possible to provide an optical disk apparatus which can be written with lower power consumption and is less expensive than an optical disk apparatus using the above-described conventional semiconductor laser element.

  An optical transmission system according to the present invention includes any one of the above semiconductor laser elements.

  According to the optical transmission system, it is possible to provide an optical transmission module that is less expensive than the conventional one and that can operate with low power consumption, and it is possible to reduce the price and improve the performance of the optical transmission system.

  As apparent from the above, according to the semiconductor laser device of the present invention, the electrode provided above the active layer (in the case of having a ridge portion, the electrode portion provided particularly in the region other than the uppermost portion of the ridge) Since it is possible to prevent the laser beam oscillated in the direction from leaking toward the electrode, it is possible to eliminate an increase in absorption loss. Accordingly, it is possible to provide a semiconductor laser device that can oscillate with a low threshold current and has high oscillation efficiency, can be operated with low power consumption and high output, and can be manufactured at low cost.

  In addition, according to the present invention, there is provided a method by which a semiconductor laser device capable of operating with high oscillation efficiency and low power consumption (low threshold current) can be easily manufactured at low cost.

  According to the optical disk apparatus of the present invention, by using the semiconductor laser element of the present invention, data can be written with low power consumption and more inexpensive than the conventional optical disk apparatus.

  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 be operated at lower cost and with lower power consumption. The transmission system can be reduced in price and performance.

  Hereinafter, a semiconductor laser device, a manufacturing method thereof, an optical disc apparatus, and an optical transmission system according to the present invention will be described in detail with reference to embodiments shown in the drawings.

  In the following description, “n−” represents the n-type as the first conductivity type, and “p−” represents the p-type as the second conductivity type. In the following description, an example in which the present invention is applied to a semiconductor laser device having a ridge structure is taken up, but the present invention is also applicable to a semiconductor laser device having no ridge structure.

[First embodiment]
FIG. 1 shows the structure of the semiconductor laser device according to the first embodiment of the present invention.

This semiconductor laser device includes an n-GaAs substrate 101, an n-GaAs buffer layer 102, an n-Al _0.5 Ga _0.5 As first lower cladding layer 103, an n-Al _0.422 Ga _0.578 As second lower cladding layer 104, an Al _0.25 Ga _0.75 As lower guide layer 105, multiple strained quantum well active layer 106, Al _0.25 Ga _0.75 As first upper guide layer 107, p-Al _0.4 Ga _0.6 As second upper guide layer as an example of the third semiconductor layer 108, p-Al _0.456 Ga _0.544 As first upper clad layer 109, p-Al _0.456 Ga _0.544 As second upper clad layer 110 as an example of the second semiconductor layer (low-concentration semiconductor layer), and p-In _0.1568 Ga _0.8432 As _0.4 P _0.6 semiconductor layers 111 are sequentially stacked.

A p-Al _0.5 Ga _0.5 As third upper cladding layer 112, a p-GaAs contact layer 113, and a first semiconductor layer (high-concentration semiconductor layer) are formed on the semiconductor layer 111 so as to form a ridge 130 having a forward mesa stripe shape. As an example, a p ⁺ -GaAs contact layer 114 is provided.

  A p-side electrode 115 made of a multilayer metal thin film formed by laminating an Al layer 115a, a Pt layer 115b, and an Au layer 115c in this order is provided on the top and side portions of the ridge 130 and on the semiconductor layer 111.

  An n-side electrode 116 made of a multilayer metal thin film of AuGe / Ni / Au is formed on the back surface of the substrate 101 as another electrode layer.

P-Al _0.4 Ga _0.6 As second upper guide layer 108, p-Al _0.456 Ga _0.544 As first upper cladding layer 109, p-Al _0.456 Ga _0.544 As second upper cladding layer 110, p-In _0.1568 Ga _0.8432 As _0.4 P _0.6 semiconductor layer 111, p-Al _0.5 Ga _0.5 As third upper cladding layer 112, p-GaAs contact layer 113 and p ⁺ -GaAs contact layer 114 constitute a second conductivity type semiconductor layer group is doing.

  Next, a method for manufacturing the semiconductor laser device will be described with reference to FIGS. FIG. 5 is an enlarged schematic view around the ridge structure of the semiconductor laser device.

First, as shown in FIG. 2, an n-GaAs buffer layer 102 (layer thickness: 0.5 μm, Si doping concentration: 7.2 × 10 ¹⁷ cm ⁻³ ) is formed on the (100) plane of the n-GaAs substrate 101. n-Al _0.5 Ga _0.5 As first lower cladding layer 103 (layer thickness: 2.0 μm, Si doping concentration: 5.4 × 10 ¹⁷ cm ⁻³ ), n-Al _0.422 Ga _0.578 As second lower cladding layer 104 ( Layer thickness: 0.1 μm, Si doping concentration: 5.4 × 10 ¹⁷ cm ⁻³ ), Al _0.25 Ga _0.75 As lower guide layer 105 (layer thickness: 3.0 nm), multiple strain quantum well active layer 106, Al _0.25 Ga _0.75 As first upper guide layer 107 (layer thickness: 3.0 nm), p-Al _0.4 Ga _0.6 As second upper guide layer 108 (layer thickness: 0.1 μm, Zn doping concentration: 1.35 × 10 ¹⁸ cm ^{− _{3), p-Al 0.456 Ga}} 0.544 As first Cladding layer 109 (thickness: 0.2 [mu] m, Zn doping ^{concentration: 1.35 × 10 18 cm -3)} , p-Al 0.456 Ga 0.544 As second upper cladding layer 110 (thickness: 0.2 [mu] m, Zn doping concentration 1 × 10 ¹⁷ cm ⁻³ ), In _0.1568 Ga _0.8432 As _0.4 P _0.6 semiconductor layer 111 (layer thickness: 15 nm, Zn doping concentration: 1 × 10 ¹⁷ m ⁻³ ), p-Al _0.5 Ga _0.5 As third Cladding layer 112 (layer thickness: 1.28 μm, Zn doping concentration: 2.4 × 10 ¹⁸ cm ⁻³ ), p-GaAs contact layer 113 (layer thickness: 0.2 μm, Zn doping concentration: 3 × 10 ¹⁸ cm ⁻⁾ at 1 × ¹⁰ 19 ^{cm -3)} in sequence, MOCVD method (metal organic chemical vapor deposition): ^3), p + -GaAs contact layer 114 (thickness: 0.3 [mu] m, Zn doping concentration To crystal growth.

The multiple strained quantum well active layer 106, In _0.1001 Ga _0.8999 As compressive strained quantum well layer (strain 0.7%, layer thickness: 4.6 nm, 2-layer) and In _0.238 Ga _0.762 As _0.5463 P _0.4537 tensile strain barrier layer (Strain 0.1%, band gap Eg≈1.60 eV, layer thickness from the substrate side: 21.5 nm, 7.9 nm, 21.5 nm, and the closest layer to the substrate 101 is the n-side barrier layer , The farthest is the p-side barrier layer).

  Next, as shown in FIG. 2, a resist mask 117 (mask width 3.5 μm) is formed on the region 117a (see FIG. 1) where the ridge 130 is to be formed by a photolithography process. The resist mask 117 is formed so as to extend in a stripe shape in the <0-11> direction corresponding to the direction in which the ridge 130 to be formed extends.

  Next, as shown in FIG. 3, by using this resist mask 117 as a mask, the ridge formation outside region 117b (see FIG. 1) corresponding to both sides of the resist mask 117 in the semiconductor layers 114, 113, and 112 is etched. By removing the ridge 130, a forward mesa stripe-like ridge 130 is formed immediately below the resist mask 117. This etching is performed up to the top of the semiconductor layer 111 using a mixed aqueous solution of sulfuric acid and hydrogen peroxide. Subsequently, overhang portions of the GaAs contact layers 113 and 114 are taken with a mixed aqueous solution of ammonia and hydrogen peroxide. The depth of etching is 1.78 μm, and the width of the lowermost portion of the ridge 130 is about 3.2 μm. After the etching is completed, the resist mask 117 is removed.

  Subsequently, as shown in FIG. 4, the electron beam evaporation method is used to form the Al layer 115a (layer thickness: 50 nm) / Pt layer 115b (layer thickness: 10 nm) / Au layer 115c (layer thickness: p-side electrode 115). A metal thin film is laminated and formed in the order of 300 nm).

  Thereafter, as shown in FIG. 1, the substrate 101 is ground from the back surface side to a desired thickness (here, about 100 μm) by a lapping method. Then, by using resistance heating vapor deposition from the back side, as the n-side electrode 116, AuGe alloy (alloy of Au 88% and Ge 12%, layer thickness: 100 nm), Ni (layer thickness: 15 nm), Au (layer thickness: 300 nm) ).

Thereafter, the electrode material is alloyed by heating at 450 ° C. for 1 minute in an N ₂ atmosphere.

  After dividing the substrate 101 into a plurality of bars having a desired resonator length (here, 800 μm), end coating is performed on the bars, and the bars are further divided into chips (800 μm × 250 μm). The chip after the division is fixed on a stem (not shown) using In glue. Then, an Au wire (not shown) for electrical connection with an external circuit is bonded on the p-side electrode 115. Thus, the semiconductor laser element is completed.

When a current is passed between the p-side electrode 115 and the n-side electrode 116 of the semiconductor laser device thus fabricated, a current is generated in a Schottky junction between the low-concentration semiconductor layer on the side of the ridge 130 and the p-side electrode 115. Is blocked, and a current flows only through an ohmic junction between the p ⁺ -GaAs contact layer 114, which is a high-concentration semiconductor layer provided on the top of the ridge 130, and the p-side electrode 115. Thereby, current confinement is performed.

  As described above, the semiconductor laser device according to the first embodiment can be manufactured much more than a semiconductor laser device having a general ridge buried structure because the crystal growth process in the manufacturing stage can be completed only once. The number of processes has been reduced, and it has become possible to produce at a low cost.

  In the semiconductor laser device of the first embodiment, the p-side electrode has an Al layer as the lowermost layer and an Au layer as the uppermost layer through a diffusion prevention layer made of Pt.

For the p ⁺ -GaAs contact layer 114 doped to 1 × 10 ¹⁹ cm ⁻³ at the top of the ridge, the p-side electrode 115 described above can realize a good ohmic junction having a low contact resistance. On the other hand, the p-Al _0.456 Ga _0.544 As second upper cladding layer 110, which is a low-concentration semiconductor layer doped to 1 × 10 ¹⁷ cm ⁻³ on the side of the ridge portion, and p-In _0.1568 Ga _0.8432 For the As _0.4 P _0.6 semiconductor layer 111, a Schottky junction having a sufficient current confinement property and stable against a long-term thermal and electrical stress could be obtained.

  This is because the Al material is very easily and rapidly oxidized in an oxygen-containing atmosphere, but the Al layer is formed in the lowest layer of the p-side electrode and further acts as a diffusion prevention layer. This is largely due to the fact that both of Pt and Au, which is the uppermost layer, are coated with a material layer that is very difficult to oxidize.

  As described above, by using the configuration of the p-side electrode in the first embodiment, it was possible to realize a semiconductor laser device having good electrical characteristics including reliability.

  Furthermore, in the semiconductor laser device of the first embodiment, by using Al for the lowermost layer of the p-side electrode provided on the ridge side, a semiconductor laser device having good optical characteristics is realized. Successful. Hereinafter, this point will be described in detail.

  In general, in a ridge waveguide type semiconductor laser element, Ti / Pt / Au that does not require alloying and does not worry about deep diffusion of the electrode material into the semiconductor layer as the electrode material formed on the ridge portion side. In many cases, an electrode configuration in which the layers are sequentially stacked is used.

  This is because an AuZn alloy frequently used in a ridge-embedded semiconductor laser element can obtain a good ohmic junction by performing an alloying process, while the diffusion of metal atoms constituting the electrode is rapid. In addition, there is a concern that it proceeds in a spike shape and increases internal scattering and absorption loss due to diffused metal atoms, and in addition, causes a decrease in reliability due to deterioration of crystallinity accompanying the progress of diffusion, This is because, in the ridge waveguide semiconductor laser element whose electrode position is close to the active layer, there is a high possibility that the effect is particularly noticeable, and this is avoided.

  However, when a Ti / Pt / Au electrode that does not require alloying is applied to a semiconductor laser device that performs current confinement using a Schottky junction as shown in the first embodiment, another problem occurs. I understand. That is, since the refractive index values of Ti and Pt are extremely close to the refractive index values of the semiconductor layers constituting the semiconductor laser element, the effect of confining the oscillation laser light in the semiconductor layer is reduced.

  For example, the refractive index of Ti is about 3.0 to 3.6 in the wavelength range of 650 nm to 1.5 μm, and Pt is 2.9 to 5.5 in the same wavelength range of 668 nm to 1.5 μm. On the other hand, the effective refractive index in the vertical direction outside the ridge is, for example, about 3 to 3.5, and the refractive index of the electrode material formed near the ridge is particularly large in the light distribution of the oscillating laser light. If the refractive index is close to the refractive index of the semiconductor layer, light tends to leak to the electrode side.

Since the absorption coefficient of a metal used as an electrode material is generally 10 ⁴ to 10 ⁵ times larger than that of a semiconductor, if light leaks to the electrode in this way, a very large absorption loss occurs. End up. It has been found that this significantly reduces the slope efficiency of the semiconductor laser element.

  On the other hand, Al used for the lowermost layer of the p-side electrode in the first embodiment has a refractive index of approximately 2 or less in a wavelength range of 100 nm to over 1 μm. The table below shows the refractive index values of the deposited Al film extracted from Chapter 6, pages 124-125 of AMERICA INSTITUTE OF PHYSICS HANDBOOK THIRD EDITION.

Table Refractive index of evaporated Al film

  As can be seen from the above table, the refractive index of the semiconductor material constituting the semiconductor laser element is about 3 to 3.5, so that the wavelength of 400 nm to 1. In light oscillating at 5 μm, the Al material has a sufficiently large refractive index difference (Δn ≧ 1) with respect to the semiconductor material. Therefore, if the Al material is used as an electrode formed on the ridge portion side, it is possible to increase the effect of confining the oscillated laser light in the semiconductor layer. For this reason, it was possible to suppress light from leaking to the electrode, and as a result, it was possible to realize a semiconductor laser device having high slope efficiency without absorption loss.

  Here, FIG. 6 shows the relationship between the thickness of the Al layer in the p-side electrode and the internal loss of the 0th-order mode. This graph assumes light with a wavelength of 900 nm (refractive index 1.96), and when an Al layer is further formed on the lowermost layer of a conventionally used Ti (50 nm) / Pt (50 nm) / Au (400 nm) electrode The amount of internal loss is simulated by calculation. As can be seen from FIG. 6, the internal loss starts to decrease when Al is inserted. Furthermore, until the thickness of the Al layer reaches about 30 nm, the internal loss rapidly decreases as the thickness of the Al layer increases. When the thickness of Al is set to 30 nm, the internal loss is reduced by 3 compared to when no Al is inserted. It can be reduced to less than 1 / minute. If the thickness of the Al layer is further increased, the internal loss is further reduced, but the degree thereof is moderate, and when the thickness is 50 nm or more, the reduction effect is lost.

Based on this result, in the first embodiment, a semiconductor laser device was fabricated with an Al layer thickness of 30 nm. In addition, when a semiconductor laser element having a conventional electrode configuration is fabricated and compared, the internal loss calculated from the actual elements having different resonator lengths of the semiconductor laser element in the present embodiment is 5 cm ^{−1, which} is a conventional Ti / Compared with 18 cm ⁻¹ , which is an actual measurement value when a Pt / Au electrode is used, it can be greatly reduced. As a result, the slope efficiency of the semiconductor laser device according to the first embodiment was more than 1.0 W / A despite the ridge waveguide type using a Schottky junction for current confinement.

  Further, in the semiconductor laser device of the first embodiment, not only Al is applied to the lowermost layer of the electrode formed on the ridge portion side, but also the uppermost Au layer is interposed through the Pt layer as the diffusion preventing layer. The electrode configuration is formed.

  In general, Au used for the electrode surface is frequently used because it has a low resistance and, in addition, has a merit that it can easily form a metal-to-metal joint using pressure welding by not oxidizing. However, if the Au layer is formed directly when Al is present in the lower layer as in the present invention, an AlAu alloy layer called purple gold is likely to be formed at the Al / Au interface. This AlAu alloy layer becomes a very high resistance interface layer, which greatly increases the series resistance of the semiconductor laser element.

  Therefore, in the electrode configuration in the first embodiment, 10 nm of Pt that acts as an Au diffusion prevention layer is formed on the Al layer. Pt has a good anti-diffusion effect for Au, and when the resistance of the electrode portion was evaluated, it was found that if a Pt layer of at least 5 nm or more is formed at the interface, the increase in resistance due to the formation of the AlAu alloy layer can be prevented. It was. In the first embodiment, the thickness of the Pt layer to be formed is determined to be 10 nm in consideration of the film thickness variation. By forming the Pt layer and the Au layer which are very difficult to oxidize on the Al layer, the oxidation of Al in the lowermost layer of the p-side electrode is prevented.

  In the step of forming the p-side electrode, a vacuum evaporation method such as an electron beam evaporation method, a sputtering method, or the like can be applied as in the manufacturing method of the first embodiment. At this time, the Al layer formed as the lowermost layer of the electrode is obtained by consistently performing the deposition from the deposition of the lowermost Al layer to the deposition of the uppermost Au layer without being exposed to the air in the middle. Oxidation during the electrode forming process is eliminated, and electrode resistance can be reduced.

In the semiconductor laser device of the first embodiment, the Zn doping concentration of the p-Al _0.456 Ga _0.544 As second upper cladding layer 110 and the In _0.1568 Ga _0.8432 As _0.4 P _0.6 semiconductor layer 111 is 1 × as described above. By setting it to 10 ¹⁷ cm ⁻³ , sufficient current confinement property could be obtained. Their total thickness is 0.215 μm. The total thickness of the semiconductor layer having the Zn doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less needs to be 0.2 μm or more in order to realize sufficient current confinement.

In the present embodiment, the semiconductor layer having a Zn doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less has a two-layer structure, but may of course have one layer or three or more layers. However, the uppermost layer is preferably InGaAsP as in the present embodiment. Since the InGaAsP semiconductor layer does not contain Al, the InGaAsP semiconductor layer is not easily oxidized, and has a great effect on maintaining (reliability) long-term current confinement. Further, since the etching characteristics are different from those of semiconductor materials such as GaAs and AlGaAs, there is an advantage that highly accurate ridge formation using selective etching is possible.

  Note that InGaP can also be used in that Al is not included in the semiconductor layer, but when applied to p-type as in this embodiment, InGaAsP has a lower barrier to holes than InGaP, and There is an effect that the hole injection efficiency can be improved.

In the semiconductor laser device of the first embodiment, the composition is the same as that of the second upper clad layer 110, but the p-Al _0.456 Ga _0.544 As first upper clad layer 109 (layer thickness: 0. 2 μm, Zn doping concentration: 1.35 × 10 ¹⁸ cm ⁻³ ) is provided between the second upper cladding layer 110 and the active layer 106, and desired optical characteristics can be obtained by changing the thickness of this layer. It is adjusted so that Of course, not only the thickness but also the composition may be changed.

As in the present embodiment, the doping concentration is increased further on the active layer side than the semiconductor layers 110 and 111 having a p-type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less provided for good current confinement. By adopting the configuration in which the semiconductor layers 108 and 109 are formed, the element resistance more than necessary can be suppressed and the deterioration of the element characteristics can be prevented.

  In the above description, the example in which the electrode configuration of the present invention is applied to an ohmic junction and a Schottky junction with respect to a p-type semiconductor layer has been shown, but the same effect can be obtained even with respect to an n-type semiconductor layer. Of course.

In the semiconductor laser device of the present embodiment, as described above, Al having a refractive index difference of 1 or more with respect to the semiconductor layer is the bottom layer, and the uppermost layer Au reacts with Al and has high resistance. It is characterized by having an electrode on the ridge side with Pt in between to prevent the formation of an interface layer. The electrode structure can obtain an ohmic junction having a low contact resistance with respect to a contact layer doped to 5 × 10 ¹⁸ cm ⁻³ or more, preferably 1 × 10 ¹⁹ cm ⁻³ or more. Sufficient current confinement can be achieved for a semiconductor layer doped to × 10 ¹⁷ cm ⁻³ or less. Furthermore, according to the above electrode configuration, the effect of confining the oscillated laser light in the semiconductor layer is great, and there is no increase in internal loss due to light leaking to the electrode.

  Therefore, sufficient current confinement can be achieved without separately performing the crystal regrowth process of the buried layer (current block layer) for current confinement and the crystal regrowth process of the contact layer for obtaining low contact resistance. It has become possible to provide a semiconductor laser device having a low contact resistance and a method for manufacturing the same.

  Further, by adopting the structure and the manufacturing method as described above, the semiconductor laser device in the first embodiment can be applied to an electrode provided on the ridge side (particularly an electrode provided in a region other than the uppermost portion of the ridge). Since the oscillation laser beam could be prevented from leaking out, it became possible to eliminate the increase in internal scattering and absorption loss. Therefore, a semiconductor laser element having high slope efficiency and capable of oscillating with a low threshold current and capable of low power consumption and high output operation can be manufactured at an overwhelmingly low cost as compared with the prior art.

  In the present embodiment, an SCH (Separate Confinement Heterostructure) structure having a guide layer between the active layer and the clad layer is used. However, the present invention is not limited to the structure described above. For example, it is a matter of course that each layer thickness, material change, and the like can be added without departing from the spirit of the present invention, such as adding an intermediate layer for smooth crystal growth.

[Second Embodiment]
FIG. 7 shows an example of the structure of the optical disc apparatus 200 according to the present invention. This is for writing data on the optical disc 201 or reproducing the written data, and the wavelength of 780 nm using the configuration of the first embodiment described above as the light emitting element used at that time. A semiconductor laser element 202 that oscillates in a band is provided.

  This optical disk device will be described in more detail. At the time of writing, the signal light L emitted from the semiconductor laser element 202 is converted into parallel light by the collimator lens 203, passes through the beam splitter 204, and 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. The recorded data signal is converted into an electric signal by the intensity of the laser beam incident in the signal detection light-receiving element 208, and is reproduced by the signal light reproducing circuit 209 to the original signal.

  In the optical disk device according to the second embodiment, since the semiconductor laser element 202 that can be manufactured at a low cost, operates with high oscillation efficiency, and has a low element resistance, the power consumption can be significantly reduced. It became. Accordingly, it is possible to provide an optical disc apparatus with less environmental load at a low cost.

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

[Third embodiment]
FIG. 8 is a cross-sectional view showing an optical transmission module 300 used in the optical transmission system according to the third embodiment of the present invention. FIG. 9 is a perspective view showing a light source portion, and FIG. 10 is a schematic diagram of an optical transmission system. In the third embodiment, the InGaAs semiconductor laser element (laser chip) 301 having the oscillation wavelength of 890 nm described in the first embodiment is used as the light source, and the silicon (Si) pin photodiode is used as the light receiving element 302. 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 optical signals between the two optical transmission modules 300 is configured. The

  In FIG. 8, a pattern of both positive and negative electrodes for driving a semiconductor laser is formed on a circuit board 306. As shown in the figure, a recess 306a having a depth of 300 μm is provided in a portion where the laser chip 301 is mounted. A laser mount (mounting material) 310 on which the laser chip 301 is mounted is fixed to the recess 306a with solder. The flat portion 313 (see FIG. 9) 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, an IC circuit 308 for laser driving / reception signal processing is mounted on the circuit board 306.

  Next, an appropriate amount of a liquid silicon resin 309 is dropped on the portion where the laser mount 310 is mounted. A filler that diffuses light is mixed in the silicon resin 309. 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 the 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 remains on the laser chip surface and its vicinity due to surface tension. 306a is not necessarily provided.

  Thereafter, it is heated at 80 ° C. for about 5 minutes to be cured until it forms a jelly. Next, it is covered with a transparent epoxy resin mold 303. Above the laser chip 301, a lens part 304 for controlling the radiation 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. As shown in FIG. 9, a laser chip 301 is die-bonded to an L-shaped heat sink 311 using In glue. The laser chip 301 is the InGaAs-based semiconductor laser element described in the first embodiment, and the 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. ing. 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 electrode region 301c provided on the Schottky junction on the surface of the laser chip 301 are connected by a gold wire 307c. As described above, the laser mount 310 is soldered to the negative electrode (not shown) of the circuit board 306 in FIG. 7, and the flat portion 313 on the upper side of the positive electrode 312 and the positive electrode portion (see FIG. (Not shown) with 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 can be manufactured at the low cost described above and uses a semiconductor laser element with high efficiency and low element resistance, the power consumption of the module is significantly lower than the conventional one. It can be suppressed and the unit price of the module can be lowered. Since the optical transmission system using the optical transmission module 300 operates with low power consumption, the load on the environment can be reduced, and the optical transmission system can be configured at a low price. Further, when this optical transmission system is mounted on a portable device, the battery driving time can be made longer than before, and the portable device can be used more comfortably.

  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. 10 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). ing. An optical signal emitted 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.

  Note that the semiconductor laser device, the optical disk device, and the optical transmission system of the present invention are not limited to the above illustrated examples. For example, various changes can be made without departing from the gist of the present invention, such as the layer thickness and the number of layers of the well layers and barrier layers.

1 is a schematic cross-sectional view of a semiconductor laser device according to a first embodiment of the present invention. It is a schematic diagram for demonstrating the manufacturing process of the semiconductor laser element of 1st embodiment of this invention, and represents the state which provided the photomask for ridge formation after crystal growth. It is a schematic diagram for demonstrating the manufacturing process of the semiconductor laser element of 1st embodiment of this invention, and represents the state after the etching process for ridge formation. It is a schematic diagram for demonstrating the manufacturing process of the semiconductor laser element of 1st embodiment of this invention, and represents the state after the vapor deposition process of a p side electrode. FIG. 3 is an enlarged schematic view around the ridge structure of the semiconductor laser device according to the first embodiment of the present invention. It is a graph which shows the relationship between the thickness of an Al electrode, and internal loss. It is the schematic of the optical disk apparatus of 2nd embodiment of this invention. It is the schematic of the optical transmission module used for the optical transmission system of 3rd embodiment of this invention. It is a perspective view of the light source concerning the optical transmission system of a third embodiment of the present invention. It is a perspective view which shows the structural example of the optical transmission system of 3rd embodiment of this invention. It is a cross-sectional schematic diagram for demonstrating the conventional semiconductor laser element and its manufacturing method.

Explanation 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 first upper guide layer 108 p -AlGaAs second upper guide layer 109 p-AlGaAs first upper cladding layer 110 p-AlGaAs second upper cladding layer 111 p-InGaAsP semiconductor layer 112 p-AlGaAs second upper cladding layer 113 p-GaAs contact layer 114 p ⁺ - GaAs contact layer 115 p-side electrode 115a Al layer 115b diffusion prevention layer 115b Au layer 116 n-side electrode 117 photoresist 117a ridge formation region 117b ridge formation outside region 130 ridge 200 optical disk device 201 Optical disk 202 Semiconductor laser element 203 Collimating lens 204 Beam splitter 205 λ / 4 polarizing plate 206 Objective lens 207 Objective lens for light receiving element 208 Signal detecting light receiving element 209 Signal light reproducing circuit 300, 300 ′ Optical transmission module 301 Semiconductor laser element (laser Chip)
301a Low reflection film 301b High reflection film 301c Schottky bonded electrode region 302 Light receiving element 303 Epoxy resin mold 304, 305 Lens part 306 Circuit board 306a Recessed part 307a, b, c Wire 308 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-type GaAs substrate 402 n-type InGaP clad layer 403 InGaAs / GaAs strained quantum well active layer 404 p-type InGaP clad layer 405 p-type InGaAs contact layer 406 p-electrode 407 n-electrode 408 Schottky junction

Claims (19)

In a semiconductor laser element having at least an active layer, a second conductivity type semiconductor layer group, and an electrode formed on the second conductivity type semiconductor layer group on a first conductivity type substrate,
The doping concentration of the second conductivity type of the first semiconductor layer in contact with the electrode in the second conductivity type semiconductor layer group is 5 × 10 ¹⁸ cm ⁻³ or more,
The semiconductor laser device, wherein the electrode includes at least an Al layer in contact with the first semiconductor layer. The semiconductor laser device according to claim 1,
The semiconductor laser device is a ridge waveguide semiconductor laser device in which a part of the upper side of the second conductivity type semiconductor layer group forms a striped ridge portion,
The first semiconductor layer constitutes the top of the ridge portion,
In the electrode, the Al layer is a surface in the vicinity of the ridge portion in a region excluding the top surface of the ridge portion and a side surface of the ridge portion, or the ridge portion of the second conductivity type semiconductor layer group. A semiconductor laser device, wherein the semiconductor laser device is formed so as to be in contact with at least one of the above. The semiconductor laser device according to claim 2,
The uppermost part of the ridge part and the electrode form an ohmic junction, and the side surface of the ridge part or the surface in the vicinity of the ridge part in the region excluding the ridge part of the semiconductor layer group of the second conductivity type A semiconductor laser element characterized in that at least one of the above and the electrode form a Schottky junction. The semiconductor laser device according to claim 1 or 2,
A semiconductor laser element, wherein the Al layer has a thickness of 30 nm or more. The semiconductor laser device according to claim 1 or 2,
The semiconductor laser device, wherein the electrode has a structure in which one or more metal thin films are further laminated on the Al layer. The semiconductor laser device according to claim 5, wherein
The electrode consists of at least three layers,
Diffusion prevention that prevents the material of at least the uppermost metal thin film layer from diffusing up to the Al layer between the lowermost Al layer and the uppermost metal thin film layer and immediately above the Al layer A semiconductor laser element, wherein a layer is formed. The semiconductor laser device according to claim 6, wherein
A semiconductor laser element, wherein the uppermost layer of the electrode is an Au layer. The semiconductor laser device according to claim 7, wherein
A semiconductor laser element, wherein the diffusion preventing layer is made of Pt. The semiconductor laser device according to claim 8, wherein
A semiconductor laser element, wherein a thickness of the diffusion preventing layer made of Pt is 5 nm or more. The semiconductor laser device according to claim 2,
The second conductivity type semiconductor layer group includes a second semiconductor layer having a second conductivity type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less,
The surface in the vicinity of the ridge portion in the region excluding the ridge portion of the semiconductor layer group of the second conductivity type is the surface of the second semiconductor layer,
The electrode is continuously formed so as to be in contact with the upper surface of the first semiconductor layer constituting the uppermost portion of the ridge portion, the side surface of the ridge portion, and the surface of the second semiconductor layer. A semiconductor laser device comprising: The semiconductor laser device according to claim 10, wherein
The semiconductor layer group of the second conductivity type includes a third semiconductor layer formed between the second semiconductor layer and the active layer and having a doping concentration greater than 1 × 10 ¹⁷ cm ⁻³ . A semiconductor laser device. Forming at least an active layer on the substrate of the first conductivity type;
On the active layer, a second conductive type semiconductor layer group including a second conductive type first semiconductor layer having a doping concentration of 5 × 10 ¹⁸ cm ⁻³ or more is exposed, and a surface of the first semiconductor layer is exposed. Forming to do,
Forming an electrode including an Al layer on the first semiconductor layer so that the Al layer is in contact with the surface of the first semiconductor layer. . In the manufacturing method of the semiconductor laser device according to claim 12,
The semiconductor layer group of the second conductivity type further includes a second semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less,
A part of the second conductivity type semiconductor layer group is removed between the step of forming the second conductivity type semiconductor layer group and the step of forming the electrode until the second semiconductor layer is exposed. A step of forming a ridge portion having the first semiconductor layer at the top,
A method of manufacturing a semiconductor laser device, comprising: forming the Al layer so as to be in contact with an upper surface of the ridge portion and at least one of a side surface of the ridge portion or an exposed surface of the second semiconductor layer. . In the manufacturing method of the semiconductor laser device according to claim 12 or 13,
In the step of forming the electrode, a method of manufacturing a semiconductor laser device, comprising forming an anti-diffusion layer on the Al layer and then forming an Au film. In the manufacturing method of the semiconductor laser device according to claim 14,
A method of manufacturing a semiconductor laser device, wherein the step of forming the electrode is performed without being exposed to the air in the middle. In the manufacturing method of the semiconductor laser device according to claim 14,
Pt is deposited as said diffusion prevention layer, The manufacturing method of the semiconductor laser element characterized by the above-mentioned. In the manufacturing method of the semiconductor laser device according to claim 12 or 13,
In the step of forming the second conductivity type semiconductor layer group, a second conductivity type third layer having a doping concentration greater than 1 × 10 ¹⁷ cm ⁻³ between the second semiconductor layer and the active layer. A method of manufacturing a semiconductor laser device, comprising forming a semiconductor layer.   An optical disc apparatus comprising the semiconductor laser element according to claim 1.   An optical transmission system comprising the semiconductor laser device according to claim 1.

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