JP2005167196A - Semiconductor laser device, its manufacturing method, optical disc, and photo transfer system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser device which is simple in structure, can operate in a high output with a threshold current, is high in reliability, and is low in cost, its manufacturing method, an optical disc, and a photo transfer system. <P>SOLUTION: A p site electrode 114 is formed on a p<SP>+</SP>-GaAs contact layer 113 of a doping concentration 1×10<SP>18</SP>cm<SP>-3</SP>or more and on a second p-AlGaAs upper clad layer 109 of a doping concentration 1×10<SP>17</SP>cm<SP>-3</SP>or more. A compound layer 115, where the material of the p site electrode 114 and the material of each semiconductor layer are alloyed, are formed on the interface of each semiconductor layer adjacent to the p site electrode 114. A low contact resistance can be obtained by ohmic junction through the compound layer 115 of a contact layer 113 and the p site electrode 114. The excellent current constriction can be obtained by Schottky junction through the compound layer 115 of the second upper clad layer 109 and the p site electrode 114. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a semiconductor laser element, a manufacturing method thereof, an optical disc apparatus, and an optical transmission system, and more particularly to a semiconductor laser element with high output and low power consumption used for an optical disc apparatus, an optical transmission system, and the like.

  In today's information society, the importance of optical disc devices, which are information recording media, and optical transmission systems for exchanging information is increasing, and the demand for them is increasing. The semiconductor laser element is a key device of these optical disk devices and optical transmission systems, and plays a very important role.

  In this semiconductor laser device, the laser oscillation output must be increased in order to write or transmit a larger amount of information on the optical disk faster. However, when a semiconductor laser element is oscillated at a high output, the deterioration generally proceeds quickly. Therefore, it is important to realize a high output while ensuring the reliability of the element. Furthermore, considering the mounting of optical disc devices and optical transmission systems on portable devices and the reduction of the load on the environment when the devices are used or manufactured as much as possible, the power consumption is smaller and the product can be manufactured at the lowest possible cost. Is also required.

As a conventional first semiconductor laser element that achieves both high reliability and low power consumption (low threshold current), there is a ridge embedded structure shown in FIG. 19 (for example, Japanese Patent Laid-Open No. 5-160503 (Patent Document 1). )reference). In this conventional first semiconductor laser element, an n-GaAs buffer layer 602, an n-Al _0.5 Ga _0.5 As lower clad layer 603, and an Al _0.15 Ga _0.85 As active layer 604 are sequentially laminated on an n-GaAs substrate 601. Further, the p-Al _0.5 Ga _0.5 As upper cladding layer 605 and the p-GaAs cap layer 606 form a ridge portion 608 while leaving a part of the p-Al _0.5 Ga _0.5 As upper cladding layer 605 in a region other than the ridge portion. ing. On both sides of the ridge portion 608, an n-AlGaAs current blocking layer 609 and an n-GaAs protective layer 610 are embedded and formed on the p-GaAs cap layer 606, the n-AlGaAs current blocking layer 609, and the n-GaAs protective layer 610. A p-GaAs contact layer 611 is provided.

  This semiconductor laser element is manufactured as follows.

(a) First, n-GaAs buffer layer 602 (layer thickness 0.5 μm), n-Al _0.5 Ga _0.5 As lower clad layer 603 (layer thickness) as the first semiconductor layer crystal growth on n-GaAs substrate 601 1.0 μm), Al _0.15 Ga _0.85 As active layer 604 (layer thickness 0.07 μm), p-Al _0.5 Ga _0.5 As upper clad layer 605 (layer thickness 1.0 μm), p-GaAs cap layer 606 (layer thickness 0) .2 μm) are successively grown by MOCVD (metal organic chemical vapor deposition) or MBE (molecular beam epitaxy) (see FIG. 20A).

  (b) Next, a dielectric film 607 such as silicon nitride or silicon oxide is formed in stripes on the p-GaAs cap layer 606, and the dielectric film 607 is used as a mask to form the p-GaAs cap layer 606 and the p-AlGaAs. A part of the upper cladding layer 605 is removed to form a ridge portion 608 (see FIG. 20B).

  (c) As the second crystal growth of the semiconductor layer, n − is selectively applied only on the side surface of the p-GaAs cap layer 606 and the p-AlGaAs upper cladding layer 605 by MOCVD growth technique using the dielectric film 607 as a mask. An AlGaAs current blocking layer 609 and an n-GaAs protective layer 610 are sequentially formed (see FIG. 20C).

  (d) Next, the dielectric film 607 is removed, and as a third crystal growth of the semiconductor layer, the p-GaAs cap layer 606, the n-AlGaAs current blocking layer 609 appearing on the surface, and the n-GaAs protection are performed. A p-GaAs contact layer 611 is formed so as to cover all of the layer 610 (see FIG. 20D).

  Finally, an electrode is formed on each of the n-GaAs substrate 601 and the p-GaAs contact layer 611 to complete the semiconductor laser device. This semiconductor laser element performs laser oscillation by confining light and current in a region immediately below the ridge portion 608 of the AlGaAs active layer 604.

  The conventional first semiconductor laser device uses a so-called ridge buried structure in which the p-AlGaAs upper cladding layer 605 has a ridge-shaped region. In this structure, the p-AlGaAs upper clad layer 605 containing Al that is easily oxidized is once exposed to the atmosphere in the step (b) after the formation of the ridge portion in the manufacturing process. In general, a portion once exposed to the atmosphere in the AlGaAs layer forms a deep level and causes light absorption, thereby reducing the reliability of the laser element. However, in this ridge embedded structure, the portion exposed to the atmosphere is away from the active region during laser oscillation, so that light absorption in this portion is suppressed to a low level and reliability can be ensured.

  In the first conventional semiconductor laser device, an n-AlGaAs current blocking layer 609 having a refractive index smaller than that of the p-AlGaAs upper cladding layer 605 is provided outside the ridge-shaped portion of the p-AlGaAs upper cladding layer 605. Therefore, the light is confined in the horizontal direction only by the current confinement and the actual refractive index. Since this so-called real refractive index guide type laser does not use light absorption for optical confinement in the horizontal direction, the waveguide loss during laser oscillation is small, and the power consumption can be kept low.

  Thus, in general, semiconductor laser elements having a ridge embedded structure are widely used as a structure that can achieve both high reliability and low power consumption. However, in the production of this structure, it is necessary to perform crystal (re) growth two more times on a semiconductor substrate on which an active layer or the like is previously laminated.

  Performing crystal regrowth twice is a significant cost increase factor in producing a semiconductor laser device. For this reason, a conventional second semiconductor laser element has been proposed in which the manufacturing process is simplified by laminating a clad layer and a Schottky junction and an ohmic junction with a contact layer (for example, Japanese Patent Laid-Open No. Hei 4- No. 111375 (see Patent Document 2).

  The conventional second semiconductor laser element will be described below. FIG. 21 is a schematic cross-sectional view of a conventional second semiconductor laser device. This conventional second semiconductor laser device is manufactured as follows.

  First, an n-InGaP clad layer 702, an InGaAs / GaAs strained quantum well active layer 703, a p-InGaP clad layer 704, and a p-InGaAs contact layer 705 are sequentially stacked on an n-GaAs substrate 701 by MOCVD. Etching is performed halfway through the p-InGaP cladding layer 704 by a method such as the above, and after forming a mesa, Ti / Pt / Au is used as the p-side electrode 706 and Au-Ge-Ni / Au is used as the n-side electrode 707 sequentially. Evaporate. When a current is passed through the device thus manufactured, a Schottky junction 708 is formed between the p-InGaP cladding layer 704 and the p-side electrode 706, and between the p-side electrode and the p-InGaAs contact layer 705. Current flows only through the current and current confinement is performed.

  By adopting a structure similar to that of the conventional second semiconductor laser element, a total of three crystal growth steps in the buried heterostructure such as the conventional first semiconductor laser element can be performed once. , Can greatly reduce the manufacturing process.

  Another conventional third semiconductor laser element that performs current confinement using this type of Schottky junction is shown in FIG. 22 (see, for example, Japanese Patent Laid-Open No. 62-281384 (Patent Document 3)). ). In FIG. 22, 801 is an n-GaAs substrate, 802 is an n-AlGaAs first cladding layer, 803 is a highly compensated Si-doped GaAs active layer, 804 is a p-AlGaAs second cladding layer, 805 is a p-GaAs layer, and 806 is A p-AlGaAs third cladding layer, 807 is a p-GaAs layer, and 808 and 809 are electrodes.

  As shown in FIG. 22, on the GaAs substrate 801, the p-AlGaAs second cladding layer 804 is exposed by using selective etching of AlGaAs and GaAs, and is then Schottky-bonded to the p-GaAs contact layer 807. Such a structure is disclosed. In the conventional third semiconductor laser device, the selective etching can be used to make the manufacturing process easy and have good controllability, and high output operation can be expected.

  As described above, the conventional ridge-embedded first semiconductor laser element has a problem of high manufacturing cost although it can achieve both high reliability and low power consumption. Further, in the second and third semiconductor laser devices that perform current confinement using a conventional Schottky junction, a low threshold current (for example, 30 mA or less), a high threshold current that is realized in a semiconductor laser device having a ridge buried structure, and the like. An output (for example, output exceeding 150 mW) operation could not be performed. Moreover, it has been difficult to design an element that meets the optical characteristic specifications required for various applications. Furthermore, the reliability of the Schottky junction is poor and long-term reliability cannot be realized.

  The reason why the low threshold current and the high output operation could not be realized is that the current confinement at the Schottky junction is insufficient, and the leakage current particularly when the fine stripe structure is used cannot be sufficiently reduced. is there.

  In addition, a configuration capable of achieving both low element resistance and current confinement is not disclosed, and as a result, element resistance increases, which is one factor that hinders high output operation.

  In order to ensure current confinement, a material system of InGaP having a large valence band energy difference ΔEv (lattice matching with GaAs) or highly mixed AlGaAs must be used for the cladding layer. The room for changing the refractive index of the cladding layer was small. For this reason, the degree of freedom in designing optical characteristics has been limited. Furthermore, the structure of the Schottky junction that is resistant to breakdown is not disclosed, and only a long-term reliability is lacking.

  In addition, for example, in the above-described conventional semiconductor laser device in the second and the manufacturing method thereof, the optical characteristics of the laser device are greatly affected by the change in the thickness of the p-InGaP cladding layer removed by etching halfway. In addition, there are problems that the horizontal far field pattern (FFP) varies and the stability of the transverse mode is deteriorated. Furthermore, when the InGaP layer thickness varies, the characteristics of the Schottky junction formed thereon also vary, and current confinement may not be sufficiently performed. Further, since the refractive index of the InGaP layer under the lattice matching condition with respect to GaAs is uniquely determined, the optical design can be adjusted only by changing the InGaP film thickness, and the degree of freedom is small. Furthermore, the use of InGaP on the p-cladding side increases ΔEv, and there are problems such as limiting the efficiency of hole injection into the active layer.

Further, in the conventional third semiconductor laser device, the controllability of the manufacturing process is improved by using selective etching of AlGaAs and GaAs. However, the shot having sufficient current confining ability to withstand high output operation with respect to AlGaAs. It was difficult to obtain a key joint, and there was a problem in terms of long-term reliability.
Japanese Patent Laid-Open No. 5-160503 JP-A-4-111375 JP-A-62-281384

  An object of the present invention is to provide a semiconductor laser device that overcomes the above-described problems, can operate at a high output with a low threshold current, has long-term reliability, and can reduce costs by simplifying the manufacturing process. In addition, an object of the present invention is to provide a semiconductor laser device that has a high degree of freedom in designing optical characteristics and can obtain stable optical characteristics.

  Another object of the present invention is to provide an optical disk device and an optical transmission system using the semiconductor laser element, a manufacturing method thereof, and the semiconductor laser element.

In order to achieve the above object, a semiconductor laser device of the present invention includes a first conductivity type substrate, an active layer formed on the first conductivity type substrate, and a second conductivity formed on the active layer. The semiconductor layer group of the second conductivity type includes at least a low-concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less and a doping concentration of 1 × 10 ¹⁸ cm. ^-3 or more high-concentration semiconductor layer, an electrode is formed on the second conductivity type semiconductor layer group, and the electrode material and the low-concentration semiconductor layer are formed at the interface between the electrode and the low-concentration semiconductor layer. A low-concentration compound layer is formed, and a high-concentration compound layer composed of the electrode material and the high-concentration semiconductor layer is formed at the interface between the electrode and the high-concentration semiconductor layer. It is characterized by being.

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 electrode, a lower contact resistance can be obtained by the high concentration side compound layer. In a Schottky junction between a low-concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less and an electrode, sufficient current confinement can be obtained by the low-concentration compound layer. Since the ohmic junction and Schottky junction are both strengthened in this way, the crystal regrowth process of the buried layer (current block layer) for current confinement and the crystal of the contact layer for low contact resistance Sufficient current constriction and low contact resistance can be realized without performing a separate regrowth process, improving thermal and electrical reliability. Therefore, low threshold current and high output operation are possible, long-term reliability can be obtained, cost can be reduced by simplifying the manufacturing process, and reliability and high output characteristics equivalent to or better than conventional semiconductor laser elements Can be realized with low power consumption.

In one embodiment, a semiconductor layer of the 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. It is preferable.

According to the semiconductor laser device of the embodiment, by further forming 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. Freedom of optical design because the thickness and composition of the second conductivity type semiconductor layer can be freely changed according to the required optical characteristic specifications without being restricted by considering Schottky junction characteristics As the degree increases, an increase in element resistance can be suppressed, and power consumption can be further reduced.

  In one embodiment, the high-concentration semiconductor layer is preferably provided on the uppermost portion of the ridge structure, and the low-concentration semiconductor layer is preferably provided on at least a region other than the uppermost portion of the ridge structure. .

  According to the semiconductor laser device of the embodiment, in the ridge structure in which the high-concentration semiconductor layer is provided at the top and the low-concentration semiconductor layer is provided in the region other than the top, the second conductivity type semiconductor layer group The same electrode formed on the high-concentration semiconductor layer and the low-concentration semiconductor layer can simultaneously form a Schottky junction part for current confinement and an ohmic junction part for current injection. A laser element can be provided.

  In one embodiment, the high-concentration semiconductor layer is preferably GaAs or InGaAs.

  According to the semiconductor laser device of the above embodiment, the device resistance is reduced without performing the step of forming the electrode contact layer by crystal regrowth by the ohmic junction between the high-concentration semiconductor layer of GaAs or InGaAs and the electrode. As a result, the cost of manufacturing the semiconductor laser device can be greatly reduced.

  In one embodiment, the low-concentration semiconductor layer is preferably AlGaAs.

  According to the semiconductor laser device of the above-described embodiment, the current blocking layer is sufficiently excellent in current confinement without making the current block layer regrown by a Schottky junction between the low-concentration semiconductor layer made of AlGaAs and the electrode. In addition, since the semiconductor laser device can be provided, the manufacturing cost can be greatly reduced.

  In one embodiment, the low-concentration semiconductor layer preferably contains at least In and P.

  According to the semiconductor laser device of the above embodiment, the current blocking layer is sufficiently confined without forming a structure in which the current blocking layer is regrown by a Schottky junction between the low-concentration semiconductor layer containing at least In and P and the electrode. Since a semiconductor laser element with excellent performance can be provided, the manufacturing cost can be greatly reduced.

  In one embodiment, the low-concentration semiconductor layer is preferably any one of InGaP, InGaAsP, InGaAlP, or InAlAsP.

  According to the semiconductor laser device of the embodiment, the low-concentration semiconductor layer is any one of InGaP, InGaAsP, InGaAlP, InAlAsP, so that selective etching can be used for the ridge formation process. Thereby, the manufacturing process can be simplified and the yield can be improved.

  In one embodiment, C, Mg, or Be is preferably used as a dopant for the second conductivity type semiconductor layer group.

  According to the semiconductor laser device of the embodiment, by using C, Mg, or Be as the dopant of the semiconductor layer group of the second conductivity type, a low concentration that forms a Schottky junction during crystal growth or device energization operation. Since the diffusion of the dopant from the upper and lower layers to the semiconductor layer is suppressed, it is possible to prevent the current confinement from being lowered due to the dopant diffusion. Therefore, it is possible to manufacture a semiconductor laser device having a good current confinement property with good controllability, and to reduce the variation during mass production and to improve the reliability during energization.

  In one embodiment, the thickness of the low concentration compound layer is preferably less than 0.2 μm.

  According to the semiconductor laser device of the embodiment, by making the thickness of the low-concentration compound layer less than 0.2 μm, an increase in the resistance of the device more than necessary due to an increase in the thickness of the low-concentration semiconductor layer is prevented. And has the effect of reducing power consumption.

  In one embodiment, the electrode is a multilayer metal thin film, and the lowermost layer of the multilayer metal thin film is preferably composed of a platinum group element or a platinum group element compound. Here, the platinum group element is a general term for ruthenium Ru, rhodium Rh, palladium Pd, osmium Os, iridium Ir, and platinum Pt, and the platinum group element compound includes Ru, Rh, Pd, Os, Ir, and Pt. It is a compound containing at least one of them.

  According to the semiconductor laser device of the embodiment, the lowermost layer of the electrode that is a multilayer metal thin film is made of a platinum group element or a platinum group element compound, so that an alloying reaction occurs between the platinum group element and the low concentration semiconductor layer. As a result, a stable Schottky junction can be obtained for the low-concentration semiconductor layer, so that it is possible to provide a semiconductor laser device having both sufficient current confinement properties and thermal and electrical reliability.

  In one embodiment, the low-concentration compound layer preferably contains a platinum group element.

  According to the semiconductor laser device of the embodiment, since the compound layer contains a platinum group element, a stable Schottky junction can be obtained for the low-concentration semiconductor layer. It is possible to provide a semiconductor laser device having both excellent reliability.

  In one embodiment, the electrode is preferably a multilayer metal thin film, and the lowermost layer of the multilayer metal thin film is preferably made of Ti.

  According to the semiconductor laser device of the embodiment, since the lowermost layer of the electrode is made of Ti, an alloying reaction is caused between Ti and the low-concentration semiconductor layer, which is stable with respect to the low-concentration semiconductor layer. Since a Schottky junction can be obtained, it is possible to provide a semiconductor laser device having both sufficient current confinement properties and thermal and electrical reliability.

  In one embodiment, the low-concentration compound layer preferably contains at least Ti.

  According to the semiconductor laser device of the embodiment, since the compound layer contains Ti, a stable Schottky junction can be obtained with respect to the low concentration semiconductor layer, so that sufficient current confinement property and thermal and electrical reliability can be obtained. It becomes possible to provide a semiconductor laser device having both properties.

  In one embodiment, the semiconductor laser device preferably has a stripe structure on both sides of the ridge structure, the uppermost portion being higher than the uppermost portion of the ridge structure.

  According to the semiconductor laser device of the embodiment, the stripe-shaped structure whose uppermost portion is higher than the uppermost portion of the ridge structure is formed on both sides of the ridge structure, and the stripe-shaped structure is a protective structure for the ridge structure. Since it acts as a body, damage to the ridge structure can be prevented and yield can be improved.

  In one embodiment, the semiconductor laser device has a stripe structure on the both sides of the ridge structure, and the uppermost side of the stripe structure is mounted on the upper side of the ridge structure. A surface is preferred. Here, the mounting surface refers to a surface on which the semiconductor laser chip comes into contact with a stem or a heat radiating body on which the semiconductor laser element is mounted.

  According to the semiconductor laser device of the above embodiment, since the top (top) side of the stripe-shaped structure whose top is higher than the top of the ridge structure is a mounting surface, the ridge structure of the semiconductor laser device Even when performing so-called junction down type mounting in which the electrode provided on the side is die-bonded to a stem or a heat radiator, there is an effect of preventing the ridge structure from being damaged.

  In one embodiment, the low-concentration semiconductor layer is preferably provided on the uppermost part of the stripe structure.

According to the semiconductor laser device of the embodiment, a separate insulator is provided for the low-concentration semiconductor layer having a second conductivity type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less formed on the top of the stripe structure. Without providing a film or the like, it is possible to create a structure capable of interrupting current at the interface between the electrode and the stripe structure by a consistent crystal growth process. Therefore, it is possible to provide a semiconductor laser device that can be manufactured at a low cost and can prevent damage to the ridge structure.

  In one embodiment, the low-concentration semiconductor layer provided on the top of the stripe structure is preferably made of InGaP or InGaAsP.

  According to the semiconductor laser device of the embodiment, by using InGaP or InGaAsP as the low-concentration semiconductor layer provided on the stripe structure, it is possible to perform sufficient current confinement without the need for providing an additional insulator film or the like. become. Furthermore, by using InGaP or InGaAsP, a favorable selective etching can be realized with the high-concentration semiconductor layer formed at the top of the ridge structure, and the manufacturing process is simplified, so that the semiconductor laser with improved yield is obtained. An element can be provided.

  In one embodiment, the stripe structure may be made of a conductor.

According to the semiconductor laser device of the embodiment, since the stripe structure is made of a conductor, when the junction down type mounting is performed, the electrode provided on the ridge structure via the stripe structure. On the contrary, there is an effect that heat generated in the active layer can be efficiently released to the outside through the stripe structure. Naturally, this heat dissipation effect is greater when the stripe structure is formed using a conductor having a higher thermal conductivity than the semiconductor layer. Furthermore, since it is not necessary to form an insulator film for interrupting current and a low-concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less on the stripe structure, the manufacturing process can be further simplified, It is possible to provide a semiconductor laser device with a good yield and low manufacturing cost.

  In one embodiment, it is preferable that the conductor is made of gold or an alloy containing gold.

  According to the semiconductor laser device of the embodiment, since the conductor is gold or an alloy containing gold, a stripe shape that achieves both low electrode resistance and good heat dissipation characteristics and is easy to perform the junction-down mounting described above. It becomes possible to provide the structure of the structure.

  In one embodiment, an insulator film may be formed so as to cover the stripe structure, and a part of the electrode may be formed on the insulator film.

  According to the semiconductor laser device of the embodiment, since an insulator film is inserted between the stripe structure and the electrode, current flows from the electrode to the active layer through the stripe structure. There is no flow. Therefore, it becomes possible to provide a semiconductor laser device having a low threshold current value without causing an excessive leakage current.

The method of manufacturing a semiconductor laser device according to the present invention includes a step of forming the active layer on a first conductivity type substrate, and a low doping concentration of at least 1 × 10 ¹⁷ cm ⁻³ on the active layer. Forming a second conductivity type semiconductor layer group including a concentration semiconductor layer and a high concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more, and forming an electrode on the second conductivity type semiconductor layer group And a step of forming a compound layer at an interface between the electrode and the second conductivity type semiconductor layer group by performing a heat treatment after the electrode is formed.

According to the method of manufacturing a semiconductor laser device of the embodiment, sufficient current confinement is obtained by the compound layer in a Schottky junction between a low concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less and an electrode. In the ohmic junction between the high concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more and the electrode, a lower contact resistance can be obtained by the compound layer. Since the Schottky junction and the ohmic junction are further strengthened in this way, a low threshold current and a high output operation can be performed without performing a current block layer burying regrowth process and an electrode contact layer crystal regrowth process. It is possible and long-term reliability can be obtained, and 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 reliability, and that can operate at high power with low power consumption.

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 ⁻³ between the low-concentration semiconductor layer and the active layer. It is preferable to form a semiconductor layer of the second conductivity type having the above doping concentration.

According to the method for manufacturing a semiconductor laser device of the embodiment, a second conductivity type semiconductor layer having a doping concentration of at least 1 × 10 ¹⁷ cm ⁻³ or more is further formed between the low-concentration semiconductor layer and the active layer. By doing so, the thickness and composition of the second conductivity type semiconductor layer can be freely changed according to the required optical characteristic specifications without being restricted in consideration of the Schottky junction characteristics. While the degree of freedom of design increases, an increase in element resistance can be suppressed, and further reduction in power consumption can be achieved.

  Also, in one embodiment of the method for manufacturing a semiconductor laser device, the step of forming the electrode comprises a platinum group element or a platinum group element compound which is the lowest layer of the electrode on the second conductivity type semiconductor layer group. It is preferable that the compound layer is made of a platinum group element or a platinum group element compound material of the lowermost layer of the electrode and a material of the second conductivity type semiconductor layer group.

  According to the method of manufacturing a semiconductor laser device of the embodiment, the lowermost layer of the electrode is made of a platinum group element or a platinum group element compound, so that an alloying reaction occurs between the platinum group element and the low concentration semiconductor layer. As a result, a stable Schottky junction can be obtained for the low-concentration semiconductor layer, so that a semiconductor laser device having both sufficient current confinement properties and thermal and electrical reliability can be manufactured.

  In one embodiment, when the lowermost layer of the electrode is composed of a platinum group element or a platinum group element compound, the heat treatment in the step of forming the compound layer is performed at 350 ° C. to 450 ° C. Are preferred.

  According to the method of manufacturing a semiconductor laser device of the embodiment, by performing a heat treatment at 350 ° C. to 450 ° C. in the step of forming the compound layer, a highly reliable Schottky junction and a sufficiently low resistance are achieved. An ohmic junction can be obtained. Therefore, it is possible to manufacture a semiconductor laser device having sufficient current confinement property, excellent device reliability, and capable of high output operation with low power consumption. Note that a sufficient alloying reaction does not occur at a heat treatment of 350 ° C. or lower, and the contact resistance of the ohmic junction increases at 450 ° C. or higher, and the Schottky bondability deteriorates.

  Also, in one embodiment of the method of manufacturing a semiconductor laser device, the step of forming the electrode includes a step of forming a layer made of Ti that is a lowermost layer of the electrode on the second conductive type semiconductor layer group. In addition, it is preferable that the compound layer contains at least Ti as a constituent element of the lowermost layer of the electrode.

  According to the method of manufacturing a semiconductor laser device of the embodiment, since the lowermost layer of the electrode is made of Ti, an alloying reaction is caused between Ti and the low concentration semiconductor layer, and Since a stable and stable Schottky junction can be obtained, it is possible to provide a semiconductor laser device having both sufficient current confinement properties and thermal and electrical reliability. Therefore, it has sufficient current confinement, excellent device reliability, and high output operation with low power consumption, without performing the current block layer burying regrowth process or electrode contact layer crystal regrowth process. It becomes possible to manufacture a simple semiconductor laser element.

  In one embodiment of the method of manufacturing a semiconductor laser device, when the lowermost layer of the electrode is made of Ti, the heat treatment in the step of forming the compound layer is preferably performed at 350 ° C. to 430 ° C.

  According to the manufacturing method of the semiconductor laser device of the embodiment, a highly reliable Schottky junction and a low-resistance ohmic junction can be obtained simultaneously. Therefore, it is possible to manufacture a semiconductor laser element that has sufficient current confinement, excellent element reliability, and low power consumption and high output operation. When the temperature is 350 ° C. or less, the reaction for forming the compound layer by alloying does not proceed sufficiently, and when the temperature exceeds 430 ° C., the contact resistance gradually deteriorates in the ohmic junction.

  In one embodiment, after the step of forming the second conductive type semiconductor layer group, the second conductive type semiconductor layer group is processed so that the high-concentration semiconductor layer is the highest. Preferably, the method includes a step of forming an upper ridge structure, and a step of forming a stripe-shaped structure having an uppermost portion higher than the uppermost portion of the ridge structure on both sides of the ridge structure.

  According to the method of manufacturing the semiconductor laser device of the embodiment, in order to form the stripe structure having the uppermost portion higher than the uppermost portion of the ridge structure on both sides of the ridge structure, Damage can be prevented.

  Also, in one embodiment of the method for manufacturing a semiconductor laser device, after the step of forming a compound layer at an interface between the electrode and the second conductivity type semiconductor layer group, the semiconductor laser device is formed on the stripe structure of the electrode. It is preferable to include the step of joining the region to the support.

  According to the method of manufacturing a semiconductor laser device of the above embodiment, when performing a so-called junction down type mounting process in which the electrode on the side on which the ridge structure is formed is joined to a support such as a stem or a radiator, Great effect to prevent damage.

In one embodiment, after the step of forming the second conductive type semiconductor layer group, a doping concentration of 1 × 10 ¹⁷ cm ⁻ is applied on the second conductive type semiconductor layer group. Forming a second low concentration semiconductor layer of ³ or less; partially removing the second low concentration semiconductor layer to expose the high concentration semiconductor layer; and exposing the high concentration semiconductor layer A portion of the region is removed until the low-concentration semiconductor layer is exposed to form a ridge structure, and after the step of forming the ridge structure, the second conductivity type including the second low-concentration semiconductor layer Forming an electrode on the semiconductor layer group.

According to the method of manufacturing a semiconductor laser device of the embodiment, as a series of crystal growth steps, the second low-concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less is used as the second conductivity type semiconductor layer. Since it can be formed on a group, there is no need to perform a crystal regrowth process or an insulating film formation process after the formation of the ridge structure, and a stripe structure in which current confinement is realized by a simple manufacturing process There is an effect that the body can be manufactured.

  In one embodiment, the second low-concentration semiconductor layer is made of InGaP or InGaAsP, and the second low-concentration semiconductor layer is partially removed to produce the high-concentration semiconductor. In the step of exposing the layer, it is preferable to perform wet etching using hydrochloric acid or a mixed solution containing hydrochloric acid.

  According to the method of manufacturing a semiconductor laser device of the embodiment, it is possible to realize a good current confinement by using a semiconductor layer made of InGaP or InGaAsP as the second low-concentration semiconductor layer. Further, in the step of removing the second low-concentration semiconductor layer, wet etching using hydrochloric acid or a mixed solution containing hydrochloric acid is performed, whereby the high-concentration semiconductor layer that is the uppermost portion of the ridge structure is subjected to the first step. The two low-concentration semiconductor layers can be selectively removed easily, and the manufacturing process can be simplified and the manufacturing variation can be reduced. Therefore, it becomes possible to manufacture a semiconductor laser device with reduced manufacturing costs.

At this time, as the mixed solution containing hydrochloric acid, a mixture of hydrochloric acid and phosphoric acid (H ₃ PO ₄ ) can be preferably used.

  Also, in one embodiment of the method for manufacturing a semiconductor laser device, in the step of forming the stripe structure, the electrode is used as a power supply metal in at least a region on the low concentration semiconductor layer of the electrode. It is preferable that the striped structure made of gold or an alloy containing gold is formed by plating.

  According to the method of manufacturing a semiconductor laser device of the embodiment, since the electrode provided on the ridge structure side is used as a power supply metal when performing electrolytic plating, there is no need to separately form and remove the power supply metal. The manufacturing process is simplified, and the manufacturing process can be performed at low cost. At this time, since the stripe structure is gold or an alloy containing gold, a semiconductor laser device having both low electrode resistance and good heat dissipation characteristics can be manufactured, and the yield of the junction-down mounting described above can be improved. It becomes possible.

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

  According to the optical disk apparatus, it is possible to provide an optical disk apparatus that is cheaper and can be written at a higher speed and is more reliable than a conventional optical disk apparatus.

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

  According to the optical transmission system, it is possible to provide an optical transmission module that is overwhelmingly cheaper and more reliable than the conventional one, and the cost of the optical transmission system can be reduced.

  As is clear from the above, according to the semiconductor laser device of the present invention, without separately performing the crystal regrowth process of the buried layer for current confinement and the crystal regrowth process of the contact layer for obtaining low contact resistance. It is possible to provide a semiconductor laser element capable of realizing reliability and high output characteristics equivalent to or higher than those of conventional semiconductor laser elements with low power consumption.

  The method of manufacturing a semiconductor laser device of the present invention has sufficient current confinement, excellent device reliability, without performing a current block layer burying regrowth step and a crystal regrowth step of an electrode contact layer, and It becomes possible to manufacture a semiconductor laser device capable of high power operation with low power consumption.

  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 that can be written at a lower cost and at a higher speed than the conventional optical disk apparatus and is excellent in reliability. .

  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 is overwhelmingly cheaper and more reliable than the conventional one. Therefore, the price of the optical transmission system can be reduced.

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

[First Embodiment]
FIG. 1 shows the structure of the 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 _0.5115 As first upper cladding layer 108, and low A p-Al _0.4885 Ga _0.5115 As second upper cladding layer 109 as an example of the concentration semiconductor layer is sequentially laminated. On this second upper clad layer 109, p _{+ -GaAs} etching stop layer 110, p-Al _0.4885 Ga _0.5115 As third upper clad layer 111, p-GaAs contact layer 112, and p ⁺ − as an example of a high-concentration semiconductor layer A GaAs contact layer 113 is provided. The p-GaAs etching stop layer 110, the p-Al _0.4885 Ga _0.5115 As third upper cladding layer 111, the p-GaAs contact layer 112, and the p ⁺ -GaAs contact layer 113 have a forward mesa stripe ridge structure (mesa stripe portion). 130 is formed. A p-side electrode 114 made of a multilayer metal thin film formed by stacking Pt / Ti / Pt / Au in this order is provided on the top and side surfaces of the ridge structure 130 and on the second upper cladding layer 109. Further, a compound layer 115 in which Pt and each semiconductor layer material are alloyed is formed at the interface between each semiconductor layer in contact with the p-side electrode 114. Further, an AuGe / Ni / Au multilayer metal thin film is formed on the back surface of the substrate 101 as the n-side electrode 116.

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 device will be described with reference to FIGS.

First, as shown in FIG. 2, an n-GaAs buffer layer 102 (layer thickness: 0.5 μm, Si doping: 8 × 10 ¹⁷ cm ⁻³ ), n on an n-GaAs substrate 101 having a (100) plane, -Al _0.453 Ga _0.547 As first lower cladding layer 103 (layer thickness: 3.0 μm, Si doping: 5 × 10 ¹⁷ cm ⁻³ ), n-Al _0.5 Ga _0.5 As second lower cladding layer 104 (layer thickness: 0) 0.24 μm, Si-doped: 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: 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: 1 × 10 17 cm -3)} , p-GaAs etching stop layer 110 (a layer 30 Å, ^{C-doped: 2 × 10 18 cm -3)} , p-Al 0.4885 Ga 0.5115 As third upper cladding layer 111 (layer thickness 1.28, C ^{doping: 2.7 × 10 18 cm -3)} , p- GaAs contact layer 112 (layer thickness: 0.2 μm, C dope: 3.3 × 10 ¹⁸ cm ⁻³ ), p ⁺ -GaAs contact layer 113 (layer thickness: 0.3 μm, C dope: 1 × 10 ²¹ cm ^{−) 3} ) Sequentially grow crystals by MOCVD. The multi-strain quantum well active layer 106 is composed of In _0.2655 Ga _0.7345 As _0.5914 P _0.4086 compression strain quantum well layer (strain 0.47%, layer thickness 50 _mm , two layers) and In _0.126 Ga _0.874 As _0.4071. P _0.5929 barrier layer (strain -1.2%, three layers from the substrate side, layer thickness 90 _mm , 50 _mm , 90 _mm , the closest to the substrate is the n side barrier layer, the farthest is the p side barrier layer Are arranged alternately.

  Next, in FIG. 2, a resist mask 117 (mask width 3.5 μm) is applied to the ridge structure forming region 118a where the ridge structure (mesa stripe portion) is to be formed, so that the stripe direction is the <0-11> direction. It is manufactured by a photolithography process.

  Next, portions other than the resist mask 117 are removed by etching to form a ridge structure 130. Etching is performed in two stages using a mixed aqueous solution of sulfuric acid and hydrogen peroxide and hydrofluoric acid, and is performed up to just above the etching stop layer 110. GaAs makes use of the fact that the etching rate by hydrofluoric acid is very slow, and makes it possible to flatten the etched surface and control the width of the mesa stripe. Finally, 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. At this time, the etching depth is 1.78 μm, and the width of the lowermost portion of the forward mesa stripe is about 3.2 μm (FIG. 3). After the etching, the resist mask 117 is removed.

  Subsequently, a metal thin film is laminated in the order of Pt (250 順 に) / Ti (500 () / Pt (500Å) / Au (4000Å) using an electron beam evaporation method to form the p-side electrode 114 (FIG. 4).

  Thereafter, the substrate 101 is ground from the back side to a desired thickness (about 100 μm in this case) by lapping, and from the back side by using resistance heating vapor deposition, AuGe alloy (Au: 88%, Ge: 12%) ) Is stacked with 1000 Ｎ, followed by Ni (150 Å) and Au (3000 Å) to form an n-side electrode 116.

Thereafter, heating is performed at 400 ° C. for 1 minute in an N ₂ atmosphere, and alloying treatment is performed on both the material of the p-side electrode 114 and the n-side electrode 116. As a result, a compound layer 115 in which Pt 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.

FIG. 5 is an enlarged schematic view for explaining a region where the compound layer 115 is formed. The thickness of the compound layer 115 is about 500 mm in the normal direction of the interface between the p-side electrode and the semiconductor layer. Therefore, in the p-Al _0.4885 Ga _0.5115 As second upper cladding layer 109, the area where the forward mesa stripe ridge structure 130 is not formed is approximately 500 mm thicker than the area immediately below the ridge structure 130. small.

  Next, the substrate 101 is divided into bars having a desired resonator length (here, 800 μm), end face coating is performed, and further, the chip is divided into chips (800 μm × 250 μm). A semiconductor laser device is completed (FIG. 1).

In the semiconductor laser device of the first embodiment, p-side electrodes 114 are formed on a plurality of semiconductor layers having different p-type doping concentrations. The p-side electrode 114 made of Pt / Ti / Pt / Au forms a compound layer 115 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. Utilizing this fact, in the semiconductor laser device of the first embodiment, p ⁺ as an example of a high concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more in the ridge structure (mesa stripe portion) 130. A compound layer on the high concentration side of Pt and GaAs that realizes a good ohmic junction is formed at the interface between the -GaAs contact layer 113 and the p-side electrode 114, and 1 × 10 ¹⁷ cm in the mesa stripe outer region 118b ^As an example of a low-concentration semiconductor layer having a doping concentration of ⁻³ or less, p-Al _0.4885 Ga _0.5115 As is an interface between the second upper cladding layer 109 and the p-side electrode 114 and exhibits a stable Schottky junction even when energized. A low concentration side compound layer of Pt and AlGaAs is formed. When the heat treatment is 350 ° C. or lower, a sufficient alloying reaction does not occur, and when the heat treatment is 450 ° C. or higher, the contact resistance of the ohmic junction increases and the Schottky bondability deteriorates. In the first embodiment, a heat treatment step at 400 ° C. for 1 minute is added in accordance with the optimum conditions for the alloying process of AuGe / Ni / Au as the n-side electrode.

As described above, by forming a high-concentration compound layer between a semiconductor layer having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more and an electrode as a high-concentration semiconductor layer, a practically sufficient contact resistance can be obtained. Can be obtained. At this time, like the semiconductor laser device of the first embodiment, by forming the high concentration semiconductor layer with a higher doping concentration, an ohmic junction having a lower contact resistance can be realized.

As will be described later, the low-concentration semiconductor layer is excellent in reliability by setting the doping concentration to 1 × 10 ¹⁷ cm ⁻³ or less and forming a low-concentration compound layer at the interface between the semiconductor layer and the electrode. Current confinement can be realized. The lower the doping concentration of the low-concentration semiconductor layer, the better the current confinement can be improved. However, when crystal growth using the usual MOCVD method or MBE (molecular beam epitaxy) method is performed, it is affected by the background impurities. The lower limit is limited to about 1 × 10 ¹⁶ cm ⁻³ . In addition, if the doping concentration is lowered too much, the device resistance increases, so that it is better not to reduce the doping concentration of the low-concentration semiconductor layer too much from that point. 1 × 10 ¹⁶ cm ⁻³ or more 1 × 10 ¹⁷ cm ⁻ A range of ³ or less is appropriate.

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 108 and the second upper cladding layer 109, it has succeeded in suppressing an increase in device resistance more than necessary. 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 500 mm (0.05 μm) with respect to the layer thickness of the second upper cladding layer 109 of 0.1 μm. In order to perform sufficient current confinement, since a semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less is required immediately below the compound layer 115, the compound layer 115 should not be so thick. According to the study by the inventors, the thickness of the compound layer 115 may be 0.2 μm at the maximum. Above this, the effect of increasing the device resistance due to the thick semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less becomes large.

  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.

  FIG. 6 shows a current-light output characteristic diagram of the semiconductor laser device of the first embodiment. In the first embodiment, an example of a semiconductor laser element of 780 nm band used for a CD-R or the like is given as an optical disk application. In the example of FIG. 6, the laser oscillation threshold current Ith = 27.3 mA, the slope efficiency SE is 0.93 W / A, and the operating current If when the optical output Po is 80 mW is 112 mA (at an ambient temperature of 25 ° C.). ). These values cannot be realized by a conventional semiconductor laser device using current confinement by a Schottky junction, and are comparable to the characteristics of a conventional ridge-embedded semiconductor laser device that requires regrowth. . When the semiconductor laser device of the first embodiment was subjected to a reliability test, stable operation for 3000 hours or more was confirmed with respect to pulse aging at 70 ° C. and 260 mW.

The optical characteristics were a vertical radiation angle of 17.5 degrees and a lateral radiation angle of 9 degrees, and a kink-free output up to 300 mW or more could be realized. The degree of freedom in this optical design is that the upper cladding layer is divided into a plurality of parts, the second upper cladding layer 109 mainly responsible for current confinement by Schottky junction, and the first upper cladding mainly used for adjustment of optical characteristics. This is because the layer 108 is separated. The doping concentration of the second upper cladding layer 109 mainly responsible for current confinement due to Schottky junction is 1 × 10 ¹⁷ cm ⁻³ or less, and the thickness is made as thin as possible within the range thicker than the compound layer 115, so that 1 The increase in element resistance due to the addition of a layer of × 10 ¹⁷ cm ^-3 or less is kept to the minimum necessary.

  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 optical disk applications that require high output characteristics, the current and voltage during operation increase, and the reliability is more severe than other applications. However, the p layer having a compound layer 115 formed by alloying Pt and an AlGaAs layer at the interface. The Schottky junction between the side electrode 114 and the second upper cladding layer 109 is very stable thermally and electrically, and is very effective for realizing long-term reliability.

  In the semiconductor laser device of the first embodiment, C is used as the p-type dopant instead of Zn, which is the most popular in the MOCVD method. By using C, dopant diffusion from the upper and lower layers to the second upper cladding layer 109 forming the Schottky junction can be reduced to an extremely low level, so that current confinement due to dopant diffusion is not lowered, and at the time of mass production This is a great merit for reducing the variation in power consumption and improving the reliability during energization. Similarly, Mg is a material that can lower the diffusion level in the MOCVD method. Of course, Zn may be used as in the prior art. In this first embodiment, since the crystal was grown by using the MOCVD method, C was applied as a dopant. However, when using Mg or MBE method as described above, the same effect can be obtained by using Be. can get.

  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. 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 ridge structure, but a dry etching method may be used as a matter of course. Furthermore, a ridge structure may be formed by combining dry etching and wet etching.

FIG. 23 shows the difference in current confinement due to the difference in doping concentration of the low concentration semiconductor layer. At this time, the semiconductor layer is a p-type AlGaAs layer, and the p-side electrode is a multilayer metal thin film formed by stacking Ti / Pt / Au in this order. A compound layer is formed at the interface between Ti and the p-type AlGaAs layer by the heat treatment after the formation of the p-side electrode. In FIG. 23, the leakage current of the semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ is almost zero in the voltage range of ⁻³ V to +3 V regardless of the number of energizations, whereas the doping concentration is 1 × 10 ^18. The leakage current of the cm ⁻³ semiconductor layer increases as the number of energizations increases. From this, if the doping concentration of the semiconductor layer bonded to the p-side electrode is 1 × 10 ¹⁷ cm ⁻³ , a good Schottky junction with no leakage current can be obtained.

FIG. 24 shows a comparison between when the InGaAs protective layer is provided on the semiconductor layer and when the semiconductor layer is exposed under the condition that the doping concentration of the semiconductor layer in FIG. 23 is 1 × 10 ¹⁷ cm ^−3. Although the leakage current is sufficiently small, it can be seen that the leakage current can be made smaller when the protective layer is provided.

[Second Embodiment]
FIG. 7 shows the structure of the semiconductor laser device according to the second embodiment of the present invention, and is a schematic cross-sectional view showing a preferred modification of the semiconductor laser device according to the first embodiment. The second embodiment is different from the semiconductor laser device of the first embodiment in that stripe structures 140 are formed on both sides of the ridge structure 130, and the p-type structure provided on the ridge structure 130 side. There is a feature that the junction down type mounting is performed in which the region on the stripe structure 140 in the side electrode 114 is die-bonded as a mounting surface.

  In the following, the configuration and manufacturing method of the stripe structure 140 formed on both sides of the ridge structure 130 will be described in particular, and description of components common to the first embodiment will be omitted.

As in the first embodiment, the semiconductor laser device of the second embodiment includes an n-GaAs buffer layer 102, an n-Al _0.453 Ga _0.547 As first lower cladding layer 103, and an n-Al _0.5 layer on an n-GaAs substrate 101. Ga _0.5 As second 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 _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. On this second upper cladding layer 109, a p-GaAs etching stop layer 110, a p-Al _0.4885 Ga _0.5115 As third upper cladding layer 111, so as to form a ridge structure (mesa stripe portion) 130 having a forward mesa stripe shape, A p ⁺ -GaAs contact layer 113 as an example of the p-GaAs contact layer 112 and the high-concentration semiconductor layer is provided. On the other hand, in addition to the p-GaAs etching stop layer 110, the p-Al _0.4885 Ga _0.5115 As third upper cladding layer 111, the p-GaAs contact layer 112, and the p ⁺ -GaAs contact layer 113, the stripe structure 140 A p-InGaP current blocking layer 119 is provided as an example of the two low-concentration semiconductor layers. Further, a multilayer formed by stacking Pt / Ti / Pt / Au in this order on the top portion, side surface portion of the ridge structure (mesa stripe portion) 130, the upper portion of the second upper cladding layer 109, and the surface of the stripe structure 140. A p-side electrode 114 made of a metal thin film is provided. Further, a compound layer 115 in which Pt and each semiconductor layer material are alloyed is formed at the interface of each semiconductor layer in contact with the p-side electrode 114, and is the same as the semiconductor laser device of the first embodiment. On the back surface of the substrate 101, a multilayer metal thin film of AuGe / Ni / Au is formed as the n-side electrode 116.

  The semiconductor laser device of the second embodiment is manufactured as follows.

First, an n-GaAs buffer layer 102, an n-Al _0.453 Ga _0.547 As first lower cladding layer 103, and an n-Al _0.5 Ga _0.5 As second lower cladding layer 104 are formed on an (100) _-plane n-GaAs substrate 101. 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 _0.5115 As first upper cladding layer 108, p-Al _0.4885 Ga _0.5115 As Second upper cladding layer 109 (layer thickness: 0.1 μm, C doping: 1 × 10 ¹⁷ cm ⁻³ ), p-GaAs etching stop layer 110 (layer thickness: 30 mm, C doping: 2 × 10 ¹⁸ cm ⁻³ ), p-Al _0.4885 Ga _0.5115 As third upper cladding layer 111 (layer thickness 1.28 μm, C doping: 2.7 × 10 ¹⁸ cm ⁻³ ), p-GaAs contact layer 112 (layer thickness: 0.2 μm, C doping) ^{: 3.3 × 10 18 cm -3)} , p + -GaAs Conta Coat layer 113 (thickness: 0.3 [mu] m, ^{C-doped: 1 × 10 21 cm -3)} , p-InGaP current blocking layer 119 (thickness 0.2 [mu] m, C-doped: 1 × 10 ¹⁷ cm ^-3) in sequence Then, the crystal is grown by the MOCVD method.

  Next, as shown in FIG. 8A, an etching resist mask 120 is formed on the stripe-shaped structure forming region 118c where the stripe-shaped structure 140 (shown in FIG. 7) is to be formed. The p-InGaP current blocking layer 119 in the other region is removed by etching using a 1: 3 mixed aqueous solution. At this time, selective etching can be similarly performed using hydrochloric acid alone without adding phosphoric acid.

  After the resist mask 120 is removed, as shown in FIG. 8B, a resist is formed on the ridge structure forming region 118a where the ridge structure 130 is to be formed and on the stripe structure forming region 118c where the stripe structure 140 is to be formed. A mask 121 is formed, and unnecessary semiconductor layers are removed by etching using a mixed aqueous solution of sulfuric acid and hydrogen peroxide water, a mixed aqueous solution of hydrofluoric acid and ammonia and hydrogen peroxide water.

  Thereafter, as shown in FIG. 8C, the top portion, the side surface portion, the second upper cladding layer 109 (118b) and the surface of the stripe structure 140 are continuously covered with the Pt / Ti / Pt / Au as shown in FIG. The p-side electrode 114 made of a multilayer metal thin film is laminated by using the electron beam evaporation method in this order.

  Next, after the substrate 101 has a desired thickness, an n-side electrode is formed in the same manner as in the first embodiment. Thereafter, after performing bar division, end face coating, and chip division, in the semiconductor laser device of the second embodiment, the top surface of the stripe structure 140 of the p-side electrode 114 is used as an example of a support. Junction down type mounting is performed for the stem (not shown).

  In the semiconductor laser device of the second embodiment, as described above, junction-down mounting is performed in which the ridge-side electrode 114 close to the active layer 106 where laser oscillation occurs is die-bonded to the stem. It is easy to dissipate the generated heat, which can improve device reliability. Also. In the second embodiment, since the stripe-shaped structure 140 whose top is higher than the ridge structure 130 by the amount of the current blocking layer 119 is provided on both sides of the ridge structure 130, the junction down type mounting is performed. When this is done, no extra stress is applied to the ridge structure 130, and the ridge structure 130 is not damaged.

In addition, since the current blocking layer 119 is formed subsequent to the contact layer 113 as a series of crystal growth steps, the manufacturing process is simplified compared to the case where a step of separately forming a current blocking insulator film or the like is performed. Can be The current blocking layer 119 is formed so as to have an impurity doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less, so that the Schottky formed at the interface even if the p-side electrode 114 is directly provided thereon. Sufficient current interruption for the barrier can be realized.

In the second embodiment, an example in which InGaP is used as the current blocking layer has been shown, but InGaAsP or AlGaAs can also be suitably used. Even when these are used, a sufficient current interruption can be realized by setting the doping concentration to 1 × 10 ¹⁷ cm ⁻³ or less. When InGaAsP is used, good selective etching can be realized even with a mixed aqueous solution of hydrochloric acid and phosphoric acid or hydrochloric acid alone, in the same manner as in the manufacturing method of the second embodiment. Further, when using AlGaAs as a current blocking layer, hydrofluoric acid is suitable as a selective etchant.

  In the second embodiment, since the p-side electrode 114 is formed on the stripe-shaped structure 140 whose uppermost portion is higher than the uppermost portion of the ridge structure 130, the stem in the junction down type mounting described above is used. In addition, with respect to the conductor of the heat radiating body, it is configured to establish electrical continuity between the p-side electrode 114 on the stripe structure 140 and current injection necessary for laser oscillation can be easily performed.

  As described above, by using the stripe structure 140, a junction-type mounting capable of improving heat dissipation and improving element reliability can be realized without damaging the ridge structure 130, and at a low manufacturing cost. A manufacturable semiconductor laser device and a manufacturing method thereof can be provided.

[Third Embodiment]
FIG. 9 shows the structure of a semiconductor laser device according to the third embodiment of the present invention. In the third embodiment, the first conductivity type is n-type, and the second conductivity type is p-type.

As shown in FIG. 9, this semiconductor laser device includes an n-GaAs buffer layer 202, an n-Al _0.5 Ga _0.5 As first lower cladding layer 203, an n-Al _0.422 Ga _0.578 As-thin film on an n-GaAs substrate 201. 2 lower cladding layer 204, Al _0.25 Ga _0.75 As lower guide layer 205, multiple strain quantum well active layer 206, Al _0.25 Ga _0.75 As first upper guide layer 207, p-Al _0.4 Ga _0.6 As second upper guide layer 208, p-Al _0.456 Ga _0.544 As first upper cladding layer 209, p-Al _0.456 Ga _0.544 As second upper cladding layer 210, and p-In _0.1568 Ga _0.8432 As _0.4 P _0.6 semiconductor layer 211 as an example of a low-concentration semiconductor layer. Laminated sequentially. On this semiconductor layer 211, a p-Al _0.5 Ga _0.5 As third upper cladding layer 212, a p-GaAs contact layer 213, a p ⁺ -In _x Ga _1-x As graded layer 214 (x = 0 → 0.5) and A p ⁺ -In _0.5 Ga _0.5 As contact layer 215 is provided as an example of the high concentration semiconductor layer. The p-Al _0.5 Ga _0.5 As third upper cladding layer 212, the p-GaAs contact layer 213, the p ⁺ -In _x Ga _1-x As graded layer 214, and the p ⁺ -In _0.5 Ga _0.5 As contact layer 215 are arranged in this order. A mesa stripe ridge structure (mesa stripe portion) 230 is formed. A p-side electrode 216 made of a multilayer metal thin film formed by stacking Ti / Pt / Au in this order is formed on the top and side surfaces of the ridge structure 230 and on the semiconductor layer 211. Further, a compound layer 217 in which Ti and each semiconductor material are alloyed is formed at the interface of each semiconductor layer in contact with the p-side electrode 216. Specifically, in the ridge structure (mesa stripe portion) 230, p ⁺ -In _0.5 Ga _0.5 As contact layer 215 and p-side electrode 216 as an example of a high-concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more. A low concentration of Ti and InGaAs as a high concentration side compound layer that realizes a good ohmic junction and having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less in the mesa stripe outer region 220b As an example of the semiconductor layer, p-In _0.1568 Ga _0.8432 As _0.4 P _0.6 A compound layer on the low concentration side of Ti and InGaAsP that exhibits stable Schottky junction even when energized at the interface between the semiconductor layer 211 and the p-side electrode 216 Is forming. Further, an AuGe / Ni / Au multilayer metal thin film is formed on the back surface of the substrate 201 as the n-side electrode 218.

P-AlGaAs second upper guide layer 208, p-AlGaAs first upper cladding layer 209, p-AlGaAs second upper cladding layer 210, p-InGaAsP semiconductor layer 211, p-AlGaAs third upper cladding layer 212, p- The GaAs contact layer 213, the p ⁺ -InGaAs graded layer 214 and the p ⁺ -InGaAs contact layer 215 constitute a second conductivity type semiconductor layer group.

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

First, as shown in FIG. 10, an n-GaAs buffer layer 202 (film thickness: 0.5 μm, Si doping: 7.2 × 10 ¹⁷ cm ⁻³ ) is formed on an (100) plane n-GaAs substrate 201. N-Al _0.5 Ga _0.5 As first lower cladding layer 203 (film thickness: 2 μm, Si doping: 5.4 × 10 ¹⁷ cm ⁻³ ), n-Al _0.422 Ga _0.578 As second lower cladding layer 204 (film thickness) : 0.1 μm, Si doping: 5.4 × 10 ¹⁷ cm ⁻³ ), Al _0.25 Ga _0.75 As lower guide layer 205 (film thickness: 30 mm), multi-strain quantum well active layer 206, Al _0.25 Ga _0.75 As first Upper guide layer 207 (film thickness: 30 mm), p-Al _0.4 Ga _0.6 As second upper guide layer 208 (film thickness: 0.1 μm, Mg doped: 1.35 × 10 ¹⁸ cm ⁻³ ), p-Al _0.456 Ga _0.544 As first upper cladding layer 209 (film thickness: 0.4 μm, Mg doped: 1.35 × 10 ¹⁸ cm ⁻³ ), p-Al _0.456 Ga _0.544 As second upper cladding layer 210 ( _Layer thickness: 0.1 μm, Mg doped: 1 × 10 ¹⁷ cm ⁻³ ), p-In _0.1568 Ga _0.8432 As _0.4 P _0.6 semiconductor layer 211 (layer thickness: 150 μm, Mg doped: 1 × 10 ¹⁷ cm ⁻³ ) P-Al _0.4885 Ga _0.5115 As third upper cladding layer 212 (layer thickness 1.28 μm, Mg doped: 2.4 × 10 ¹⁸ cm ⁻³ ), p-GaAs contact layer 213 (layer thickness: 0.2 μm, Mg Dope: 3 × 10 ¹⁸ cm ⁻³ ), p ⁺ -In _x Ga _1-x As graded layer 214 (layer thickness: 500 mm, x = 0 → 0.5, Mg dope: 1 × 10 ²⁰ cm ⁻³ ) and p ⁺ -In _0.5 Ga _0.5 As contact layer 215 (layer thickness: 0.1 μm, Mg doped: 1 × 10 ²⁰ cm ⁻³ ) is successively grown by MOCVD. The multiple strained quantum well active layer 206, In _0.1001 Ga _0.8999 As compressive strained quantum well layer (strain 0.7%, layer thickness: 46 Å, 2-layer) and In _0.238 Ga _0.762 As _0.5463 P _0.4537 barrier layer (strain 0. 1%, Eg≈1.60 Ev, layer thickness from the substrate side: 215 mm, 79 mm, and 215 mm, the layer closest to the substrate 201 is the n-side barrier layer, and the farthest is the p-side barrier layer) They are arranged alternately.

  Next, in FIG. 10, a resist mask 219 (mask width 4.5 μm) is applied to the ridge structure formation region 220a where the ridge structure (mesa stripe portion) 230 is to be formed, so that the stripe direction is the <0-11> direction. It is manufactured by a photolithography process.

  Next, as shown in FIG. 11, portions other than the resist mask 219 are removed by etching to form a ridge structure (mesa stripe portion) 230. Etching is performed with a mixed aqueous solution of sulfuric acid and hydrogen peroxide solution until the p-InGaAsP semiconductor layer 211 is exposed, and the GaAs contact layer 213 and the InGaAs graded layers 214 and 215 are mixed with a mixed aqueous solution of hydrofluoric acid, ammonia and hydrogen peroxide solution. The p-AlGaAs third upper clad layer 212 is arranged in a normal mesa shape so as not to have an overhang shape. The depth of etching is 1.63 μm, and the width of the lowermost portion of the ridge structure 230 having a forward mesa stripe shape is about 3.5 μm. After the etching, the resist mask 219 is removed.

  Next, as shown in FIG. 12, a metal thin film is laminated in the order of Ti (1000 Å) / Pt (500 Å) / Au (4000 Å) using an electron beam evaporation method to form a p-side electrode 216.

Thereafter, the substrate 201 is ground from the back surface side to a desired thickness (about 100 μm in this case) by lapping, and from the back surface side, resistance heating vapor deposition is used to form an AuGe as an n-side electrode 218 (shown in FIG. 9). An alloy (Au: 88%, Ge: 12%) is formed in a thickness of 1000%, followed by Ni (150%) and Au (3000%). Thereafter, heating is performed at 390 ° C. for 1 minute in an N ₂ atmosphere, and alloying treatment of Ti and AuGe / Ni materials is performed.

  Subsequently, after the substrate 201 is divided into bars having a desired resonator length (here, 500 μm), end face coating is performed and further divided into chips (500 μm × 200 μm), whereby the third embodiment of the present invention. The semiconductor laser device shown in FIG. 9 is completed.

  The third embodiment is an infrared communication semiconductor laser element having a wavelength of 890 nm. A description of the same configuration as that of the first embodiment will be omitted, and differences will be described below.

In this third embodiment, a Ti / Pt / Au multilayer metal thin film is used as the p-side electrode 216, and an alloying reaction is caused between Ti and the semiconductor layer by applying heat treatment after the electrode formation. Yes. When Ti is deposited on the semiconductor layer and heated to about 400 ° C., the oxide layer formed on the surface of the semiconductor layer is removed during the manufacturing process, and a low-doped semiconductor layer of 1 × 10 ¹⁷ cm ⁻³ or less is removed. Thus, a stable Schottky junction can be obtained. When Ti is formed and appropriately heated for the InGaAsAs layer of the third embodiment or the AlGaAs layer of the first embodiment, a particularly thermally and electrically stable Schottky junction can be obtained. This is presumably because a very thin Ti alloyed layer is formed at the interface between the electrode and the semiconductor layer, and the effect of obtaining such a stable Schottky junction is not seen unless heat treatment is performed.

In addition to the oxide layer removing effect described above, a TiAs layer can be formed for a GaAs or InGaAs layer doped to 1 × 10 ¹⁸ cm ⁻³ or more, thereby realizing a low contact resistance.

The heat treatment temperature suitable for these reactions is 350 ° C. or higher and 430 ° C. or lower. When the temperature is 350 ° C. or lower, the reaction of forming the compound layer by alloying does not proceed sufficiently, and when the temperature exceeds 430 ° C., the contact resistance gradually deteriorates in the ohmic junction. It is considered that the resistance deterioration at 430 ° C. or more is caused by the generation of the Ti ₁ Ga _1-x layer and the mixing of the metal material above the Ti. Also in the third embodiment, in consideration of the optimum heat treatment condition of the AuGe / Ni / Au electrode material on the back surface side, a heat treatment was performed at 390 ° C. for 1 minute.

  As in the third embodiment, a semiconductor layer 211 containing at least In and P is formed on the AlGaAs second upper cladding layer 210, and the semiconductor layer 211 is used as an etching stop layer at the time of ridge formation. Manufacturing variations during manufacturing are reduced, and a semiconductor laser device having stable device characteristics can be easily obtained.

  In particular, the AlGaAs second upper cladding layer 210 is not exposed, and the surface is made of InGaAsP layer that does not contain Al, so that there is no formation of deep levels as seen in AlGaAs exposed to the atmosphere, and surface recombination is also prevented. Since it is suppressed, there is an effect that the reliability at the time of element operation is greatly improved. This effect can also be obtained with InGaP that does not contain Al. However, when InGaP is used, there is no room for composition change because the In mixed crystal ratio lattice-matched to GaAs is uniquely determined, and the barrier on the hole side Since ΔEv is large, there is a demerit that hole injection efficiency into the active layer is reduced. When InGaAsP is used, the degree of freedom in composition selection is large, and the hole injection efficiency can be improved as compared with InGaP.

  The semiconductor laser device according to the third embodiment has an oscillation threshold current Ith = 10.0 mA, a slope efficiency SE = 0.85 W / A, and an operating current at an optical output of 150 mW is 186.5 mA (at an ambient temperature of 25 ° C. ). The COD (end face breakdown) level is 200 mW or more, and a semiconductor laser device having a low threshold and high output comparable to that of a semiconductor laser having a ridge embedded structure can be realized. Furthermore, in a reliability test at 85 ° C. and 120 mW using the semiconductor laser device of the third embodiment, it was confirmed that stable operation for 1000 hours or more was confirmed, and the reliability was sufficient for infrared communication applications.

[Fourth Embodiment]
FIG. 13 shows the structure of the semiconductor laser device according to the fourth embodiment of the present invention, and shows a preferred modification (No. 1) of the semiconductor laser device according to the third embodiment.

  In the semiconductor laser device of the fourth embodiment shown in FIG. 13, in addition to the structure of the semiconductor laser device of the third embodiment described above, the stripe structure forming regions 220c on both sides of the ridge structure 230 are formed by a gold plating method. It is characterized by having a stripe-shaped structure 240 made of the formed conductor.

  The manufacturing method of the semiconductor laser device of the fourth embodiment is the same up to the step of forming the p-side electrode 216 of the semiconductor laser device of the third embodiment. Thereafter, as shown in FIG. 14, the ridge structure is formed by gold electroplating using the p-side electrode 216 as a power supply metal, with the exception of the stripe structure formation region 220c masked by the photoresist 222 prior to the substrate etching step. A stripe-shaped structure 240 whose uppermost portion is higher than the uppermost portion of 130 is formed. At this time, the height of the uppermost portion of the stripe structure 240 is set to 2.5 μm, which is higher than the height of the uppermost portion of the ridge structure 130 (1.63 μm). After the plating is finished, the photoresist 222 is removed.

  Thereafter, substrate etching, n-side electrode deposition / alloy are performed, and the chip is divided into a desired chip size.

  In the following manufacturing process of the fourth embodiment, wire bonding is not performed on a semiconductor laser device in a normal chip state, and instead, the uppermost part (top) of the stripe structure 240 is applied to a stem as an example of a support. Junction down type mounting as the mounting surface is performed.

  Also in the semiconductor laser device of the fourth embodiment, as described above, junction down type mounting is performed in which the stripe structure 240 made of a conductor formed on the active layer 206 side where laser oscillation occurs is die-bonded to the stem. Therefore, it is easy to dissipate the heat generated in the active layer 206, and the device reliability can be improved. At this time, since the stripe structure 240 is formed so that the uppermost portion of the ridge structure 230 is higher than the uppermost portion of the ridge structure 230, extra stress is applied to the ridge structure 230 even when the junction down type mounting is performed. In other words, the ridge structure 230 is not damaged.

  Further, in the semiconductor laser device of the fourth embodiment, the stripe structure 240 formed in the heat dissipation path between the active layer 206 and the stem or the heat dissipator is made of a conductor excellent in heat conduction. It has a good effect on improving reliability.

  Further, according to the configuration of the fourth embodiment, there is an effect that the step of forming the current blocking layer or the insulating film in place of the current blocking layer in the second embodiment described above becomes unnecessary.

  In the semiconductor laser device of the fourth embodiment, the stripe-shaped structure 240 is formed using gold plating, but it is of course not limited thereto. From the viewpoint of electrical continuity to the stem and heat radiating body and heat radiating, any conductive material may be used.

  However, gold or an alloy containing gold is preferable because it is difficult to oxidize and the contact resistance with other metals can be lowered. When gold or an alloy containing gold is used as the material of the stripe structure, the height is easily reduced by deformation due to its soft material property, and the height difference with respect to the ridge structure is about 0.5 μm or more. Better.

  In the semiconductor laser device of the third embodiment, the ridge structure is divided so as to be offset from the center of the chip so as to facilitate wire bonding. In the fourth embodiment, both sides of the ridge structure 230 are provided. Since the wire bonding is not performed, it is not necessary to offset the ridge structure, and conversely, the center of the chip is applied so that force is applied evenly to each of the two stripe structures on both sides of the ridge structure. It is preferable that a ridge structure is formed on the substrate.

[Fifth Embodiment]
FIG. 15 shows the structure of the semiconductor laser device according to the fifth embodiment of the present invention. A modified example (part 2) suitable for the junction-down mounting of the semiconductor laser device according to the third embodiment is shown. It is shown.

The semiconductor laser device according to the fifth embodiment has the same semiconductor layer as that of the ridge structure 230 (p-Al _0.5 Ga _0.5 As third upper cladding layer 212, p-GaAs contact layer 213, p ⁺ -In _x Ga _1-x As graded layer 214 (x = 0 → 0.5) and p ⁺ -In _0.5 Ga _0.5 As contact layer 215). Further, an insulator film 223 made of silicon nitride (SiNx) is formed on the surface of the semiconductor layer with a thickness of 2000 mm, and a p-side electrode 216 is provided on the insulator film 223. Thus, the stripe structure 240 is formed in the stripe structure formation regions 220c on both sides of the ridge structure 230. The stripe structure 240 is higher than the top of the ridge structure 230 because the insulator film 223 is formed as compared with the ridge structure 230.

  At the time of junction down type mounting, the uppermost (top) side of the stripe structure 240 is a mounting surface, and instead of performing wire bonding, it is die-bonded to a heat dissipating member called a submount as an example of a support. did. The semiconductor laser device of the fifth embodiment is completed by further mounting a chip mounted on the submount on the stem and mounting it on the stem. By providing the striped structure 240 on both sides of the ridge structure 230, the ridge structure 230 can be prevented from being damaged by providing the stripe-shaped structures 240 whose uppermost part is higher than the uppermost part of the ridge structure 230.

  In the fifth embodiment, since the insulator film 223 is inserted at the interface between the semiconductor layer constituting the stripe structure 240 and the p-side electrode 216, the stripe-like structure 240 is interposed from the p-side electrode 216. Thus, no current flows to the active layer 206 side. Therefore, it is possible to provide a semiconductor laser device that does not cause an excessive leakage current, and thus has a low threshold current value, and can perform junction-down mounting without damaging the ridge structure 230. .

  In the fifth embodiment, a silicon nitride film is used as the insulator film 223, but a silicon oxide film can also be used as an alternative. In contrast to organic insulating film materials, these insulating films can be formed relatively easily, have an advantage of being easy to process after film formation and having excellent reliability.

  The thickness of the insulator film 223 formed on the stripe structure 240 is preferably at least 1000 mm in order to ensure a difference in height from the ridge structure 230 and sufficient insulation. However, there is a tradeoff between the film formation time and the stress generation when the film is thickened, and the upper limit is preferably set to 2500 mm or less. In this fifth embodiment, the thickness is 2000 mm, but the insulation against current leakage and the ridge protection at the time of junction down type mounting are sufficient.

  In the semiconductor laser device of the third embodiment, the ridge structure is divided into chips so as to facilitate wire bonding, but in this fifth embodiment, both sides of the ridge structure 230 are arranged. Since the wire bonding is not performed, it is not necessary to offset the ridge structure, and conversely, the center of the chip is applied so that force is applied evenly to each of the two stripe structures on both sides of the ridge structure. It is preferable that a ridge structure is formed on the substrate.

  Moreover, it is a matter of course that the constituent elements of the respective embodiments described above are interchanged with each other.

[Sixth Embodiment]
FIG. 16 shows an example of the structure of an optical disc apparatus 300 according to the sixth embodiment of the present invention. This is for writing data on the optical disc 301 or reproducing the written data. As the light emitting element used at that time, the semiconductor according to the first or second embodiment of the present invention described above is used. A laser element 302 is provided.

  This optical disk device will be described in more detail. At the time of writing, the signal light emitted from the semiconductor laser element 302 is converted into parallel light by the collimator lens 303, passes through the beam splitter 304, the polarization state is adjusted by the λ / 4 polarizing plate 305, and then the objective lens 306. Is condensed and irradiated onto the optical disc 301.

  At the time of reading, the optical disc 301 is irradiated with a laser beam carrying no data signal along the same path as at the time of writing. This laser beam is reflected on the surface of the optical disc 301 on which data is recorded, passes through the laser beam irradiation objective lens 306 and the λ / 4 polarizing plate 305, and then is reflected by the beam splitter 304 to change the angle by 90 °. The light is condensed by the light receiving element objective lens 307 and is incident on the signal detecting light receiving element 308. The recorded data signal is converted into an electric signal by the intensity of the laser light incident in the signal detecting light receiving element, and is reproduced by the signal light reproducing circuit 309 to the original signal.

  Since the optical disk apparatus according to the sixth embodiment uses a semiconductor laser element that can be produced at a lower cost than the conventional one and operates at a high optical output, data can be read and written even if the rotational speed of the disk is further increased. Became possible. Therefore, the access time to the disk, which has been a problem particularly at the time of writing, is significantly shorter than that of a conventional apparatus using a semiconductor laser element, and an optical disk apparatus that can be operated more comfortably can be provided at a low cost.

  Here, an example in which the semiconductor laser device of the present invention is applied to a recording / reproducing optical disc apparatus has been described. However, an optical disc recording apparatus, an optical disc reproducing apparatus using the same wavelength band of 780 nm, and other wavelength bands (for example, 650 nm band). It goes without saying that the present invention can also be applied to other optical disc apparatuses.

[Seventh Embodiment]
FIG. 17 is a cross-sectional view showing an optical transmission module 400 of the optical transmission system in the seventh embodiment of the present invention. FIG. 18 is a perspective view showing a light source portion. In the seventh embodiment, an InGaAs semiconductor laser element (laser chip 401) having an oscillation wavelength of 890 nm described in the third embodiment is used as a light source, and a silicon (Si) pin photodiode is used as the light receiving element 402. . In this optical transmission system, it is assumed that the other party that transmits and receives signals also includes the same optical transmission module as described above.

  In FIG. 17, a pattern of both positive and negative electrodes for driving a semiconductor laser is formed on a circuit board 406. As shown in the figure, a recess 406a having a depth of 300 μm is provided in a portion where a laser chip is mounted. A laser mount (mounting material) 410 on which the laser chip 401 is mounted is fixed to the recess 406a with solder. The flat portion 413 of the positive electrode 412 of the laser mount 410 is electrically connected to a laser driving positive electrode portion (not shown) on the circuit board 406 by a wire 407a. The concave portion 406a 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 402 is also mounted on the circuit board 406, and an electric signal is taken out by the wire 407b. In addition to this, an IC (integrated circuit) 408 for laser driving / reception signal processing is mounted on the circuit board 406.

  Next, an appropriate amount of a liquid silicon resin 409 is dropped on a portion where the laser mount 410 fixed to the concave portion 406a is mounted with solder. A filler that diffuses light is mixed in the silicon resin 409. The silicon resin 409 stays in the recess due to the surface tension, covers the laser mount 410 and fixes it to the recess 406a. In the seventh embodiment, a recess is provided on the circuit board 406 and the laser mount 410 is mounted. However, as described above, the silicon resin 409 stays on the laser chip surface and its vicinity due to surface tension. It is not always necessary to provide it.

  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 403. A lens portion 404 for controlling the radiation angle is formed on the upper surface of the laser chip, and a lens portion 405 for condensing the signal light is integrally formed on the upper surface of the light receiving element as a molded lens.

  Next, the laser mount 410 will be described with reference to FIG. As shown in FIG. 18, a laser chip 401 is die-bonded to an L-shaped heat sink 411 using In glue. The laser chip 401 is the InGaAs-based semiconductor laser element described in the third embodiment, and the laser chip lower surface 401b is coated with a high reflection film, while the laser chip upper surface 401a is coated with a low reflection film. Has been. These reflective films also serve as protection for the end face of the laser chip.

  A positive electrode 412 is fixed to the base 411 b of the heat sink 411 with an insulator so as not to be electrically connected to the heat sink 411. The positive electrode 412 and the electrode region 401c provided on the Schottky junction on the surface of the laser chip 401 are connected by a gold wire 407c. As described above, the laser mount 410 is fixed to the negative electrode (not shown) of the circuit board 406 of FIG. 17 by soldering, and the flat part 413 on the upper side of the positive electrode 412 and the positive electrode part of the circuit board 406 (see FIG. (Not shown) with a wire 407c. By forming such wiring, the optical transmission module 400 that can obtain the laser beam 414 by oscillation is completed.

  As the light source (laser chip) of the optical transmission module 400, not only the semiconductor laser element of the third embodiment described above but also the semiconductor laser element of the fourth or fifth embodiment can be used. In that case, since the laser chip 401 is mounted on the heat sink 411 in a junction down type, the pattern of both positive and negative electrodes on the circuit board 406 is changed, and the positive electrode and the negative electrode are connected in reverse to the case of the above embodiment. Such a configuration may be adopted.

  By using the semiconductor laser device of the fourth or fifth embodiment, the heat generated during laser oscillation can be radiated more effectively, so that an optical transmission module with higher reliability can be realized.

  As described above, in this optical transmission system, it is assumed that the other party holds another optical transmission module and transmits and receives an optical signal. The optical signal emitted from the light source with information is received by the light receiving element of the counterpart optical transmission module, and the optical signal transmitted from the counterpart is received by the light receiving element.

  An example of an optical transmission system using the optical transmission module 400 is shown in FIG. This optical transmission system includes the above-described optical transmission module 400 in both the personal computer 415 and the base station 416 installed on the ceiling of the room, and uses them as a terminal and a server, respectively, to realize data communication using light (infrared rays). It is.

  Since the optical transmission module 400 of the seventh embodiment uses the single growth type semiconductor laser element 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.

  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, and depart from the gist of the present invention, such as the layer thickness and the number of layers of the well layers and barrier layers. Of course, various modifications can be made within the range not to be performed. For example, although Pt / Ti / Pt / Au is used as the p-side electrode in the first or second embodiment and Ti / Pt / Au is used in the third to fifth embodiments, these may be switched. .

  In the first to fifth embodiments, the first conductivity type is n-type and the second conductivity type is p-type. However, the first conductivity type may be p-type and the second conductivity type may be n-type.

FIG. 1 is a schematic cross-sectional view of a plane perpendicular to the stripe direction of the semiconductor laser device according to the first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a plane perpendicular to the stripe direction after completion of the stripe formation mask process of the semiconductor laser device. FIG. 3 is a schematic cross-sectional view of a plane perpendicular to the stripe direction after completion of the mesa stripe formation etching process of the semiconductor laser device. FIG. 4 is a schematic cross-sectional view of a plane perpendicular to the stripe direction after the formation of the p-side electrode of the semiconductor laser element. FIG. 5 is a schematic cross-sectional view illustrating a Pt alloyed compound layer. FIG. 6 is a graph showing current-light output characteristics of the semiconductor laser device. FIG. 7 is a schematic cross-sectional view of a plane perpendicular to the stripe direction of the semiconductor laser device according to the second embodiment of the present invention. FIG. 8A is a diagram illustrating a manufacturing process of a modified example of the semiconductor laser element. FIG. 8B is a diagram for explaining the manufacturing process of the semiconductor laser element following FIG. 8A. FIG. 8C is a view for explaining the manufacturing process of the semiconductor laser element following FIG. 8B. FIG. 9 is a schematic cross-sectional view of a plane perpendicular to the stripe direction of the semiconductor laser device according to the third embodiment of the present invention. FIG. 10 is a schematic cross-sectional view of a plane perpendicular to the stripe direction after completion of the stripe formation mask process of the semiconductor laser device. FIG. 11 is a schematic cross-sectional view of a plane perpendicular to the stripe direction after the mesa stripe formation etching process of the semiconductor laser device is completed. FIG. 12 is a schematic cross-sectional view of a plane perpendicular to the stripe direction after forming the p-side electrode and the n-side electrode of the semiconductor laser element. FIG. 13 is a schematic cross-sectional view of a plane perpendicular to the stripe direction of the semiconductor laser device according to the fourth embodiment of the present invention. FIG. 14 is a schematic cross-sectional view illustrating the manufacturing process of the semiconductor laser device. FIG. 15 is a schematic cross-sectional view of a plane perpendicular to the stripe direction of the semiconductor laser device according to the fifth embodiment of the present invention. FIG. 16 is a schematic view of an optical disc apparatus according to the sixth embodiment of the present invention. FIG. 17 is a schematic view of an optical transmission module used in the optical transmission system according to the seventh embodiment of the present invention. FIG. 18 is a perspective view of a laser mount of the optical transmission system. FIG. 19 is a schematic cross-sectional view showing a ridge embedding structure of a conventional first semiconductor laser device. FIG. 20A is a diagram for explaining a manufacturing process of the conventional first semiconductor laser device. 20B is a diagram for explaining the manufacturing process of the ridge-embedded semiconductor laser device subsequent to FIG. 20A. FIG. 20C is a diagram for explaining the manufacturing process of the ridge-embedded semiconductor laser device subsequent to FIG. 20B. FIG. 20D is a diagram for explaining the manufacturing process for the ridge-embedded semiconductor laser device subsequent to FIG. 20C. FIG. 21 is a schematic cross-sectional view of a conventional second semiconductor laser device. FIG. 22 is a schematic cross-sectional view of a conventional third semiconductor laser device. FIG. 23 is a diagram showing the relationship between voltage and leakage current. FIG. 24 is a diagram illustrating the relationship between voltage and leakage current. FIG. 25 is a schematic diagram showing an embodiment of the optical transmission system according to the seventh embodiment of the present invention.

Explanation of symbols

101, 201 ... n-GaAs substrate 102, 202 ... n-GaAs buffer layer 103, 203 ... n-AlGaAs first lower cladding layer 104, 204 ... n-AlGaAs second lower cladding layer 105, 205 ... AlGaAs lower guide layer 106 , 206 ... Multi-strain quantum well active layer 107 ... AlGaAs upper guide layer 108, 209 ... p-AlGaAs first upper clad layer 109, 210 ... p-AlGaAs second upper clad layer 110 ... p-GaAs etching stop layer 111, 212 ... p-AlGaAs third upper cladding layer 112,213 ... p-GaAs contact layer 113 ... p ⁺ -GaAs contact layer 114,216 ... p-side electrode 115,217 ... compound layer 116,218 ... n-side electrode 117,219 ... Resist mask 118a, 220a ... Ridge structure formation region 118b, 220b ... Mesa stripe outer region 118c, 220c ... Stripe structure formation region Area 119 ... p-InGaP current blocking layer 120, 121 ... resist mask 130,230 ... ridge structure 140,240 ... stripe structure 207 ... AlGaAs first upper guide layer 208 ... p-AlGaAs second upper guide layer 211 ... p -InGaAsP semiconductor layer 214 ... ^p.sup . ⁺ -InGaAs graded layer 215 ... ^p.sup . ⁺ -InGaAs contact layer 222 ... resist mask 223 ... insulator film 300 ... optical disc apparatus 301 ... optical disc 302 ... semiconductor laser element 303 ... collimator lens 304 ... beam splitter 305 ... λ / 4 polarizing plate 306 ... objective lens 307 ... light receiving element objective lens 308 ... signal detection light receiving element 309 ... signal light reproducing circuit 400 ... light transmission module 401 ... laser chip 401a ... laser chip upper surface 401b ... laser chip lower surface 401c ... Electrode region 402 ... Light receiving element 03 ... epoxy resin mold 404, 405 ... lens 406 ... circuit board 406a ... recess 407a, 407b, 407c ... Wire 408 ... IC
409 ... Silicon resin 410 ... Laser mount 411 ... Heat sink 411b ... Base 412 ... Positive electrode 413 ... Flat part 414 ... Laser beam 415 ... Personal computer 416 ... Base station 601 ... n-GaAs substrate 602 ... n-GaAs buffer layer 603 ... n -AlGaAs lower clad layer 604 ... AlGaAs active layer 605 ... p-AlGaAs upper clad layer 606 ... p-GaAs cap layer 607 ... dielectric film 608 ... ridge portion 609 ... n-AlGaAs current blocking layer 610 ... n-GaAs protective layer 611 ... p-GaAs contact layer 701 ... n-GaAs substrate 702 ... n-InGaP clad layer 703 ... InGaAs / GaAs strained quantum well active layer 704 ... p-InGaP clad layer 705 ... p-InGaAs contact layer 706 ... p-side electrode 707 ... n-side electrode 708 ... Schottky junction 801 ... n-GaAs substrate 8 02 ... n-type AlGaAs first cladding layer 803 ... highly compensated Si-doped GaAs active layer 804 ... p-AlGaAs second cladding layer 805 ... p-GaAs layer 806 ... p-AlGaAs third cladding layer 807 ... p-GaAs layer 808 ... Electrode 809 ... Electrode

Claims (33)

In a semiconductor laser device having a first conductivity type substrate, an active layer formed on the first conductivity type substrate, and a second conductivity type semiconductor layer group formed on the active layer,
The semiconductor layer group of the second conductivity type includes at least a low concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less and a high concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more,
An electrode is formed on the semiconductor layer group of the second conductivity type,
At the interface between the electrode and the low-concentration semiconductor layer, a low-concentration compound layer made of the electrode material and the low-concentration semiconductor layer material is formed,
A semiconductor laser device, wherein a compound layer on a high concentration side made of the material of the electrode and the material of the high concentration semiconductor layer is formed at an interface between the electrode and the high concentration semiconductor layer. The semiconductor laser device according to claim 1,
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. The semiconductor laser device according to claim 1 or 2,
The high-concentration semiconductor layer is provided on the top of the ridge structure;
The semiconductor laser device, wherein the low-concentration semiconductor layer is provided at least in a region other than the uppermost portion of the ridge structure. The semiconductor laser device according to any one of claims 1 to 3,
A semiconductor laser element, wherein the high-concentration semiconductor layer is GaAs or InGaAs. The semiconductor laser device according to any one of claims 1 to 4, wherein
A semiconductor laser device, wherein the low concentration semiconductor layer is AlGaAs. The semiconductor laser device according to any one of claims 1 to 4, wherein
A semiconductor laser element, wherein the low-concentration semiconductor layer contains at least In and P. The semiconductor laser device according to claim 6, wherein
2. The semiconductor laser device according to claim 1, wherein the low concentration semiconductor layer is any one of InGaP, InGaAsP, InGaAlP, or InAlAsP. The semiconductor laser device according to any one of claims 1 to 7,
A semiconductor laser element, wherein C, Mg, or Be is used as a dopant of the second conductivity type semiconductor layer group. The semiconductor laser device according to any one of claims 1 to 8,
The semiconductor laser device according to claim 1, wherein the thickness of the low concentration compound layer is less than 0.2 μm. The semiconductor laser device according to any one of claims 1 to 9,
A semiconductor laser device, wherein the electrode is a multilayer metal thin film, and a lowermost layer of the multilayer metal thin film is made of a platinum group element or a platinum group element compound. The semiconductor laser device according to any one of claims 1 to 9,
The semiconductor laser device, wherein the low concentration compound layer contains a platinum group element. The semiconductor laser device according to any one of claims 1 to 9,
A semiconductor laser element, wherein the electrode is a multilayer metal thin film, and the lowermost layer of the multilayer metal thin film is made of Ti. The semiconductor laser device according to any one of claims 1 to 9,
The semiconductor laser device, wherein the low concentration compound layer contains at least Ti. The semiconductor laser device according to claim 3,
2. A semiconductor laser device according to claim 1, wherein a stripe structure is provided on both sides of the ridge structure, the uppermost portion being higher than the uppermost portion of the ridge structure. The semiconductor laser device according to claim 14, wherein
A semiconductor laser device, wherein the uppermost side of the stripe structure is a mounting surface. The semiconductor laser device according to claim 14, wherein
The semiconductor laser device, wherein the low-concentration semiconductor layer is provided on an uppermost portion of the stripe structure. The semiconductor laser device according to claim 16, wherein
A semiconductor laser device, wherein the low-concentration semiconductor layer provided on the uppermost portion of the stripe structure is made of InGaP or InGaAsP. The semiconductor laser device according to claim 14, wherein
A semiconductor laser element, wherein the stripe structure is made of a conductor. The semiconductor laser device according to claim 18, wherein
A semiconductor laser device, wherein the conductor is made of gold or an alloy containing gold. The semiconductor laser device according to claim 14, wherein
An insulator film is formed so as to cover the stripe structure,
A semiconductor laser element, wherein a part of the electrode is formed on the insulator film. Forming the active layer on a first conductivity type substrate;
A semiconductor layer of a second conductivity type including at least a low concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less and a high concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more on the active layer. Forming a group;
Forming an electrode on the semiconductor layer group of the second conductivity type;
A method of manufacturing a semiconductor laser device, comprising: forming a compound layer at an interface between the electrode and the second conductivity type semiconductor layer group by performing a heat treatment after forming the electrode. In the manufacturing method of the semiconductor laser device according to claim 21,
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 is provided between the low concentration semiconductor layer and the active layer. A method of manufacturing a semiconductor laser device, comprising: forming a semiconductor laser device. In the manufacturing method of the semiconductor laser device according to claim 21 or 22,
The step of forming the electrode includes a step of forming a layer made of a platinum group element or a platinum group element compound which is a lowermost layer of the electrode on the semiconductor layer group of the second conductivity type,
The method for manufacturing a semiconductor laser device, wherein the compound layer is made of a material of a platinum group element or a platinum group element compound in a lowermost layer of the electrode and a material of the semiconductor layer group of the second conductivity type. In the manufacturing method of the semiconductor laser device according to claim 23,
A method of manufacturing a semiconductor laser device, wherein the heat treatment in the step of forming the compound layer is performed at 350 ° C. to 450 ° C. In the manufacturing method of the semiconductor laser device according to claim 21 or 22,
The step of forming the electrode includes a step of forming a layer made of Ti which is the lowermost layer of the electrode on the semiconductor layer group of the second conductivity type,
The method of manufacturing a semiconductor laser device, wherein the compound layer includes at least Ti as a constituent element of the lowermost layer of the electrode. A method of manufacturing a semiconductor laser device according to claim 25,
A method of manufacturing a semiconductor laser device, wherein the heat treatment in the step of forming the compound layer is performed at 350 ° C. to 430 ° C. In the manufacturing method of the semiconductor laser device according to claim 21,
After the step of forming the second conductivity type semiconductor layer group, processing the second conductivity type semiconductor layer group to form a ridge structure having the high-concentration semiconductor layer at the top;
Forming a stripe structure on both sides of the ridge structure, the uppermost portion of the ridge structure being higher than the uppermost portion of the ridge structure. In the manufacturing method of the semiconductor laser device according to claim 27,
A step of forming a compound layer at an interface between the electrode and the semiconductor layer group of the second conductivity type, and a step of bonding a region of the electrode on the stripe structure to a support. A method for manufacturing a semiconductor laser device. In the manufacturing method of the semiconductor laser device according to claim 21,
After the step of forming the second conductivity type semiconductor layer group, a step of forming a second low concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less on the second conductivity type semiconductor layer group. When,
Partially removing the second low concentration semiconductor layer to expose the high concentration semiconductor layer;
Removing a part of the exposed region of the high-concentration semiconductor layer until the low-concentration semiconductor layer is exposed to form a ridge structure;
And a step of forming an electrode on the second conductive type semiconductor layer group including the second low-concentration semiconductor layer after the step of forming the ridge structure. The method of manufacturing a semiconductor laser device according to claim 29,
The second low-concentration semiconductor layer is made of InGaP or InGaAsP,
Manufacturing of a semiconductor laser device, wherein wet etching is performed using hydrochloric acid or a mixed solution containing hydrochloric acid in the step of partially removing the second low-concentration semiconductor layer to expose the high-concentration semiconductor layer. Method. In the manufacturing method of the semiconductor laser device according to claim 27,
In the step of forming the stripe structure, the stripe structure made of gold or an alloy containing gold by electrolytic plating using the electrode as a power supply metal in at least a region on the low concentration semiconductor layer of the electrode. A method of manufacturing a semiconductor laser device, wherein a body is formed.   21. An optical disc apparatus using the semiconductor laser element according to claim 1.   21. An optical transmission system using the semiconductor laser device according to claim 1.

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