JP2005203746A - Semiconductor laser device and manufacturing method thereof and optical disk device and light transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser device that has an excellent heat dissipation property and a handling property and can prevent dielectric breakdown and whose ridge is not easily broken, and to provide a manufacturing method of the same. <P>SOLUTION: When the shortest distance between an active layer 106 and upper electrodes (114, 116) is Hc, the height of the ridge 100 is Hr, the film thickness of each upper electrode (114, 116) on both sides of an upper clad lower layer 109 in the ridge 100 is He, and a distance in a direction moving away from the ridge 100 in parallel with a substrate with a lower ridge on the inclined plane in the ridge 100 as an origin is x, a relationship He>Hr is satisfied within a range of x≤(Hc+He)tan45°. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a semiconductor laser device, a manufacturing method thereof, an optical disc apparatus, and an optical transmission system.

  Conventionally, as a semiconductor laser device, there is a ridge waveguide type device having a ridge portion on an active layer and manufactured by a single crystal growth. This semiconductor laser device has an advantage that the semiconductor laser device can be manufactured at low cost because the manufacturing process is simpler than that of the ridge embedded semiconductor laser device that requires three crystal growth steps.

  FIG. 9 shows a cross-sectional view of a ridge waveguide type semiconductor laser device that performs current confinement using a Schottky junction without using an insulator film for current confinement (for example, Japanese Patent Laid-Open No. 4-111375 (Patent Document). 1)). This semiconductor laser device is manufactured as follows.

  First, as shown in FIG. 9, an n-InGaP cladding layer 402, an InGaAs / GaAs strained quantum well active layer 403, and a p-type substrate are formed on an n-GaAs substrate 401 by metal organic chemical vapor deposition (MOCVD). After the InGaP cladding layer 404 and the p-InGaAs contact layer 405 are sequentially stacked and etched to the middle of the p-InGaP cladding layer 404 by a technique such as photolithography, a mesa is formed. Au-Ge-Ni / Au is sequentially deposited as Pt / Au as the n-side electrode 407. When a current is passed through the device thus fabricated, a Schottky junction 408 is formed between the p-InGaP cladding layer 404 and the p-side electrode 406, and the p-side electrode and the p-InGaAs contact layer 405 are connected. Current flows only between them, and current confinement is performed.

  By adopting such a ridge waveguide type semiconductor laser element structure, a crystal growth process of one time is required in which a total of three crystal growth steps are required in the manufacturing process of a conventional semiconductor laser element with a ridge buried structure. It becomes possible to manufacture in the process, and the manufacturing process can be greatly reduced.

  However, the conventional ridge waveguide type semiconductor laser device has the following problems. That is, in a semiconductor laser device, heat generated in the vicinity of an active layer during laser oscillation operation is generally dissipated to a metal package or stem through a substrate, but as described above, a ridge waveguide semiconductor In the laser element, the active layer is formed near the extreme surface layer on the side opposite to the substrate, so that heat dissipation is poor. This is due to the poor thermal conductivity of the semiconductor substrate material. Due to the poor heat dissipation characteristics, the temperature of the element rises during high output operation, and as a result, the threshold current increases and sufficient high output operation cannot be performed, or long-term element reliability decreases. There was a problem.

  Furthermore, since the ridge structure is not embedded by the regrowth process and is exposed, there is a problem that the ridge portion is easily damaged unless care is taken in handling.

The former problem of heat dissipation is generally taken by reducing the thickness of the substrate. However, if the substrate is made thinner, the mechanical strength is lowered, so that a new problem arises that handling becomes difficult. Furthermore, in the ridge waveguide semiconductor laser device that performs current confinement using the conventional Schottky junction described above, the insulation of the Schottky junction is reduced when the substrate thickness is reduced and the distance between the upper electrode and the lower electrode is reduced. There is a problem that a destructive failure mode occurs.
Japanese Patent Laid-Open No. 4-111375 (page 3, FIG. 1)

  The present invention overcomes these problems, has good heat dissipation characteristics and handling properties, and can prevent dielectric breakdown in a configuration in which current confinement is performed using a Schottky junction, and the ridge portion is not easily damaged. It is an object of the present invention to obtain a waveguide type semiconductor laser device and a manufacturing method thereof. That is, an object of the present invention is to provide a semiconductor laser device that can be manufactured at a low cost and a high yield, and that is capable of low threshold current oscillation and high output operation, and has excellent long-term reliability, and a manufacturing method thereof.

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

  The semiconductor laser device of the present invention includes an active layer formed on a first conductivity type substrate and a second conductivity type semiconductor layer group formed on the active layer. A semiconductor laser element in which a part of the upper side of the semiconductor layer group forms a striped ridge portion, and an upper electrode is formed so as to cover the second conductivity type semiconductor layer group including the ridge portion, At least the surface of the upper electrode in a region wider than the area of the upper surface of the ridge portion is a mounting surface.

  According to the semiconductor laser device having the above configuration, the heat generated in the active layer during operation can be efficiently dissipated to the upper electrode side without passing through the substrate side having relatively poor thermal conductivity, so that the high power operation is achieved. It is possible to provide a semiconductor laser device suitable for the above and having long-term reliability. Further, since the heat is radiated without passing through the substrate as described above, it is not necessary to make the thickness of the substrate thinner than the conventional one, and as a result, the mechanical strength is not lowered, so that good handling properties can be obtained. Here, the mounting surface refers to a bonding surface when the semiconductor laser device is mounted on an external package, a heat radiator such as a stem or a heat sink.

  In one embodiment of the present invention, the semiconductor laser device includes a dummy ridge portion that is part of the upper side of the second conductivity type semiconductor layer group and is higher than the height of the ridge portion on both sides of the striped ridge portion. The upper electrode is formed so as to cover the semiconductor layer group of the second conductivity type including the ridge portion and the dummy ridge portion.

  According to the semiconductor laser device of the embodiment, the dummy ridge portion formed on both sides of the ridge structure acts as a protective structure for the ridge structure because its height is higher than the ridge portion, In combination with the upper electrode covering the second conductivity type layer including the ridge portion and the dummy ridge portion, damage to the ridge structure can be prevented and the yield can be improved.

  In one embodiment, the dummy ridge portion includes the same semiconductor layer group as the ridge portion and an insulator film provided on the surface of the semiconductor layer group constituting the dummy ridge portion. Features.

  According to the semiconductor laser device of the above embodiment, the semiconductor layer constituting the dummy ridge portion is made the same as the ridge portion, and an insulator film is formed on the surface of the dummy ridge portion, so that the height is higher than that of the ridge portion. By providing dummy ridges on both sides of the ridge that are higher than the ridge, it is possible to prevent damage to the ridge even when the upper electrode side is the mounting surface. Become.

  In one embodiment, the dummy ridge portion has a current blocking layer that forms a Schottky junction with the upper electrode formed on the dummy ridge portion on the same semiconductor layer group as the ridge portion. It is characterized by having.

  In one embodiment of the present invention, the dummy ridge portion includes a current blocking layer made of a first conductivity type semiconductor layer on the same semiconductor layer group as the ridge portion.

  According to the semiconductor laser device of the above-described embodiment, a semiconductor layer group structure capable of blocking current injection into the dummy ridge portion can be obtained without providing a separate insulator film. Since this semiconductor layer group can be produced by a consistent crystal growth process, it can be manufactured at a low cost. On the other hand, the dummy ridge portion has a current blocking layer and is higher than the ridge portion. Even in the configuration in which the side is the mounting surface, the ridge portion is not damaged.

In one embodiment, the shortest distance in the thickness direction from the active layer to the upper electrode is Hc, the height in the thickness direction of the ridge portion is Hr, and both sides of the ridge portion are When the film thickness of the upper electrode is He, and the distance in the direction parallel to the plane of the substrate and away from the ridge portion is x, with the lower edge of the inclined surface of the ridge portion as a base point, at least x Within the range of ≦ (Hc + He),
He> Hr
It is preferable to satisfy the following conditions.

  According to the semiconductor laser device of the above embodiment, the heat generated in the active layer during the operation of the semiconductor laser device is efficiently radiated to the upper electrode provided on the surface on the upper cladding layer side. At this time, from the distribution of heat radiation on the surface of the upper electrode, the thickness He of the upper electrode is set to the height of the ridge when the distance x from the lower edge of the inclined surface of the ridge is at least (Hc + He) tan 45 ° or less. By making it larger than Hr, the heat radiation characteristic to the upper electrode can be optimized. As a result, the temperature characteristics of the semiconductor laser device are improved, and an increase in the threshold current can be suppressed even when operating at a higher temperature. Further, since both sides of the ridge portion are covered with the upper electrode higher than the ridge portion, there is an effect that physical damage of the ridge portion can be prevented.

  In the semiconductor laser device of one embodiment, a heat radiator may be connected to the region of the upper electrode that satisfies at least the condition of He> Hr.

  According to the semiconductor laser device of the above embodiment, the heat generated from the active layer can be effectively diffused to the external heat sink through the upper electrode, and the temperature characteristics of the semiconductor laser device can be further improved. .

  In one embodiment, the upper electrode is a multilayer metal film, and the uppermost layer in the region of the multilayer metal film that satisfies at least the condition of He> Hr is made of gold or a gold alloy. Also good.

  According to the semiconductor laser device of the above embodiment, the use of gold or a gold alloy for the uppermost layer in the region of the multilayer metal film improves the heat conduction characteristics and further promotes heat dissipation during operation.

  In one embodiment, the ratio of the thickness of the uppermost layer made of gold or a gold alloy to the total thickness of the multilayer metal film in a region satisfying at least the condition of He> Hr is 9/10. The above is desirable.

  According to the semiconductor laser device of the above embodiment, when a thick upper electrode exceeding the height Hr of the ridge portion is formed, the ratio of the thickness of the gold or gold alloy having a good thermal conductivity to the total thickness is 9 By using / 10 or more, heat generation in the upper electrode structure can be minimized. At the same time, the stress applied to the semiconductor laser element can be further reduced by using gold having a low hardness as compared with the case where the thick upper electrode is formed using another metal.

In the semiconductor laser device of one embodiment, within the range of x ≦ (Hc + He),
He> 3Hr
It is desirable to satisfy the following conditions.

  According to the semiconductor laser of the above embodiment, the upper electrode can be a good protector for the ridge portion, and the ridge portion is also damaged when the upper electrode is connected to the heat sink by thermocompression bonding. Can be avoided.

  In one embodiment, the thickness of the region in the vicinity of the chip end of the upper electrode may be smaller than the thickness of the other region of the upper electrode.

  According to the semiconductor laser device of the above-described embodiment, a structure is provided that can be more easily divided into chips while favorably dissipating heat generated during operation of the semiconductor laser device.

  In the semiconductor laser device of one embodiment, current confinement may be performed on the ridge portion using a Schottky junction between the upper electrode and the semiconductor layer group on both sides of the ridge portion.

According to the semiconductor laser device of the above embodiment, current confinement can be performed without providing an insulating layer between the upper electrode and the semiconductor layer group, and good heat dissipation can be achieved with respect to the semiconductor laser device that can be manufactured at low cost. An electrode structure having characteristics can be added. Here, even in a general air ridge structure, it is possible to sufficiently increase the heat dissipation effect by applying this electrode structure, and silicon nitride (SiN _x ) or silicon oxide is used as an insulating layer of the air ridge structure. (SiO ₂ ) can be used.

In one embodiment, 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. The above-mentioned high concentration semiconductor layer, and at the interface between the upper electrode and the low concentration semiconductor layer, on the low concentration side comprising at least one of the constituent elements of the upper electrode and at least one of the constituent elements of the low concentration semiconductor layer A compound layer is formed, and a high-concentration compound layer comprising at least one of the constituent elements of the upper electrode and at least one of the constituent elements of the high-concentration semiconductor layer is formed at the interface between the upper electrode and the high-concentration semiconductor layer. Preferably it is formed.

According to the semiconductor laser device of the above embodiment, in the ohmic junction between the high concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more and the upper electrode, a lower contact resistance is obtained by the high concentration side compound layer. In addition, in the Schottky junction between the low concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less and the upper electrode, a sufficient current confinement can be obtained by the low concentration side 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, and thermal and electrical reliability is improved. In this way, the manufacturing process is simplified, and the upper electrode having better heat dissipation characteristics is provided, so that it oscillates at a low threshold current, enables high output operation, and provides long-term reliability. By simplifying the process, the cost can be reduced, and a semiconductor laser device capable of realizing reliability and high output characteristics equivalent to or higher than those of a semiconductor laser device having a conventional structure with low power consumption can be provided.

In one embodiment, 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. Preferably it is.

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

  In one embodiment, the high-concentration semiconductor layer is provided at the top of the ridge portion, and the low-concentration semiconductor layer is provided at least in a region other than the top of the ridge portion. preferable.

  According to the semiconductor laser device of the above embodiment, in the structure in which the high concentration semiconductor layer is provided at the uppermost portion of the ridge portion and the low concentration semiconductor layer is provided in the region other than the uppermost portion, the semiconductor layer of the second conductivity type The same upper electrode formed on the high-concentration semiconductor layer and the low-concentration semiconductor layer of the group can simultaneously form a Schottky junction portion for current confinement and an ohmic junction portion for current injection, greatly increasing the manufacturing cost. A semiconductor laser device that can be reduced can be provided.

  In one embodiment, the thickness of the substrate may be 80 μm or more.

  According to the semiconductor laser device of the above embodiment, it is possible to suppress an increase in electric field strength due to the approach of the distance between the upper electrode and the lower electrode, and dielectric breakdown during operation in the semiconductor laser device that performs current confinement using a Schottky junction. Failure due to can be suppressed.

  The method of manufacturing a semiconductor laser device of the present invention includes a step of forming an active layer on a first conductivity type substrate, a step of forming a second conductivity type semiconductor layer group on the active layer, A step of removing a part of the upper side of the two-conductivity-type semiconductor layer group to form a striped ridge portion, and a thin-film electrode so as to cover the second-conductivity-type semiconductor layer group including the ridge portion Forming a thick film electrode on at least the regions on both sides of the ridge portion of the thin film electrode, and forming an upper electrode whose surface is a mounting surface by the thin film electrode and the thick film electrode. It is said.

  According to the method of manufacturing the semiconductor laser device of the above embodiment, the thin film electrode is formed so as to cover the second conductivity type semiconductor layer group including the ridge portion, and at least on both sides of the ridge portion of the thin film electrode. A method of forming a thick film electrode is provided, and a semiconductor laser device having a configuration in which heat generated in the active layer is efficiently radiated to the upper electrode side can be manufactured.

  In one embodiment of the method for manufacturing a semiconductor laser device, in the step of forming the thin film electrode, a multilayer metal film made of gold or a gold alloy is formed as an uppermost layer, and the thin film electrode is formed in the step of forming the thin film electrode. It is desirable to form the thick film electrode by plating using the electrode as a power supply metal.

  According to the method of manufacturing a semiconductor laser device of the above embodiment, the thin film electrode formed on the entire substrate surface on the side where the ridge structure is formed is used as a power supply metal for the thick film electrode formed later by plating. Since it can be made to act, it is not necessary to perform a separate power supply metal process, and the manufacturing cost is reduced. At this time, the uppermost layer of the thin film electrode is made of gold (Au), so that the resistance of the feeding metal can be reduced and the plating current can be lowered.

  Further, in the above plating, the region near the chip end is covered with a resist mask, and after forming a thick film electrode made of gold, the gold layer on the uppermost layer of the thin film electrode in the region near the chip end is not used without using a mask such as a separate resist. By lightly etching to such an extent that is removed, gold on the uppermost layer of the thin-film electrode in the divided area at the time of end face coating or chip division can be removed. If gold remains, because it is rich in ductility and malleability, division defects are likely to occur. However, the above configuration can prevent defects during chip division.

  In one embodiment of the method of manufacturing a semiconductor laser device, the thick film electrode is made of gold or a gold alloy, and includes a step of thermocompression bonding a radiator to at least the thick film electrode regions on both sides of the ridge portion. May be.

  According to the manufacturing method of the semiconductor laser device of the above embodiment, it is not necessary to separately provide a substance serving as a paste material between the electrode and the heat radiating body, so that the heat dissipation is not deteriorated. Further, there is an effect that it is possible to prevent a mounting defect such that the paste material rises on the side surface of the semiconductor laser element and is electrically short-circuited.

In the method of manufacturing a semiconductor laser device according to one embodiment, in the step of forming the second conductivity type semiconductor layer group, a low concentration of at least a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less is formed on the active layer. Forming a second conductive type semiconductor layer group comprising a semiconductor layer and a high-concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more, and performing a heat treatment after the formation of the thin-film electrode; It is preferable to include a step of forming a compound layer at the interface with the second conductivity type semiconductor layer group.

According to the method for manufacturing the semiconductor laser device of the above embodiment, sufficient current confinement can be obtained by the compound layer in the Schottky junction between the low concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less and the thin film electrode. At the same time, a lower contact resistance can be obtained by the compound layer in the ohmic junction between the high-concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more and the thin film electrode. Since the Schottky junction and ohmic junction are further strengthened in this way, low threshold current oscillation and high output operation can be achieved without performing the burying regrowth process of the current blocking layer and the crystal regrowth process of the electrode contact layer. There is provided a method for manufacturing a semiconductor laser device that is capable of providing long-term reliability and having excellent heat dissipation characteristics that can reduce costs 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 the method of manufacturing a semiconductor laser device according to one embodiment, in the step of forming the second conductivity type semiconductor layer group, at least 1 × 10 ¹⁷ cm ⁻ between the low concentration semiconductor layer and the active layer. It is preferable to form a second conductivity type semiconductor layer having a doping concentration of ³ or more.

According to the method of manufacturing a semiconductor laser device of the above embodiment, a second conductivity type semiconductor layer having at least a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or more is further provided between the low concentration semiconductor layer and the active layer. By forming, the thickness, composition, etc. of the second conductivity type semiconductor layer can be freely changed according to the required optical characteristic specification without being restricted in consideration of the Schottky junction characteristics. Therefore, it is possible to manufacture a semiconductor laser element having a high degree of freedom in optical design, and to suppress an increase in element resistance, and thus it is possible to manufacture a semiconductor laser element capable of further lower power consumption operation. Become.

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

  According to the above optical disk apparatus, it is possible to provide an optical disk apparatus excellent in reliability that can be written at a lower cost and at a higher speed than a conventional optical disk apparatus.

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

  According to the above 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 apparent from the above, according to the semiconductor laser device of the present invention, the heat generated in the active layer during the operation of the ridge waveguide type semiconductor laser device is efficiently provided on the surface on the semiconductor layer group side. It becomes possible to radiate heat to the electrode. That is, from the heat radiation distribution on the surface of the upper electrode, the thickness He of the upper electrode is made larger than the height Hr of the ridge in the range where the distance x from the lower edge of the inclined surface of the ridge is at least (Hc + He). By increasing the size, the heat dissipation characteristics to the upper electrode can be optimized. As a result, a semiconductor laser element having improved long-term reliability that can improve the temperature characteristics of the semiconductor laser element, has a low threshold current oscillation in which an increase in the threshold current is suppressed even when operating at a higher temperature, and can operate at a high output. be able to.

  Furthermore, since both sides of the ridge portion are covered with the upper electrode higher than the ridge portion, physical damage of the ridge portion can be prevented. As a result, damage during handling of the semiconductor laser element can be reduced, and the manufacturing yield can be improved.

  In addition, in a ridge waveguide semiconductor laser device that performs current confinement using a Schottky junction, it is possible to provide a device structure that prevents breakdown due to dielectric breakdown and has excellent heat dissipation characteristics. As a result, the manufacturing cost can be further reduced.

  According to the method of manufacturing a semiconductor laser device of the present invention, a semiconductor having excellent heat dissipation characteristics as described above, low-cost and high-yield manufacturing, low threshold current oscillation, and high-output operation and excellent long-term reliability. It is possible to provide a method for manufacturing a laser element.

  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 disc apparatus, and an optical transmission system according to the present invention will be described in detail with reference to embodiments shown in the drawings.

(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. However, the first conductivity type may be p-type and the second conductivity type may be n-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 As an example of the concentration semiconductor layer, a p-Al _0.4885 Ga _0.5115 As second upper clad lower layer 109 is sequentially laminated.

On the second upper cladding lower layer 109, a p-GaAs etching stop layer 110, a p-Al _0.4885 Ga _0.5115 As second upper cladding upper layer 111, a p-GaAs contact layer 112, and a high-concentration semiconductor constituting the ridge portion 100. A p ⁺ -GaAs contact layer 113 as an example of the layer is provided to form a striped ridge portion 100. A p-side electrode 114 as a base of an upper electrode made of a multilayer metal film formed by stacking Ti / Pt / Au in the order of Ti / Pt / Au on the top and side surfaces of the ridge portion 100 and the second upper clad lower layer 109; Have

  Further, a compound layer (shown in FIG. 10) in which Ti and at least one of the constituent elements of each semiconductor layer are alloyed is formed at the interface between each semiconductor layer in contact with the p-side electrode 114. On the back surface of the n-GaAs substrate 101, an Au-Ge-Ni / Au multilayer metal thin film is formed as the n-side electrode 115. Further, a bump electrode 116 as an example of a thick film electrode made of Au is provided on the p-side electrode 114 so as to cover the ridge portion 100. The upper surface of the bump electrode 116 becomes a mounting surface to be joined to a heat radiator (not shown) provided outside.

P-Al _0.4885 Ga _0.5115 As first upper cladding layer 108, p-Al _0.4885 Ga _0.5115 As second upper cladding lower layer 109, p-GaAs etching stop layer 110, p-Al _0.4885 Ga _0.5115 As second upper cladding upper portion The layer 111, the p-GaAs contact layer 112, and the p ⁺ -GaAs contact layer 113 constitute a second conductivity type semiconductor layer group.

In the first embodiment, the shortest distance Hc from the active layer 106 to the upper electrodes on both sides of the ridge portion 100 is Al _0.4278 Ga _0.5722 As upper guide layer 107 and p-Al _0.4885 Ga _0.5115 As first upper cladding layer. 108 and p-Al _0.4885 Ga _0.5115 As second upper clad lower layer 109. The height Hr of the ridge portion 100 is determined by the p-GaAs etching stop layer 110, the p-Al _0.4885 Ga _0.5115 As second upper clad upper layer 111, the p-GaAs contact layer 112, and the p ⁺ -GaAs contact layer 113. Total thickness. The film thickness He of the upper electrode is the film thickness of the p-side electrode 114 + the height of the bump electrode 116 in the formation area of the bump electrode 116, and the area of the p-side electrode 114 in the area where the bump electrode 116 is not formed. The film thickness. The bump electrode 116 has He> Hr within a range satisfying at least x ≦ (Hc + He), where x is a distance in a direction away from the ridge portion 100 with the lower edge of the inclined surface of the ridge portion 100 as a base point. It is formed at a height that satisfies the conditions. Further, only the Ti film and the Pt film among the Ti film, the Pt film, and the Au film constituting the p-side electrode 114 are formed at the chip end portion 117 of the semiconductor laser element.

  Next, a manufacturing method of the semiconductor laser element will be described with reference to FIGS. 2A to 2D.

First, as shown in FIG. 2A, an n-GaAs buffer layer 102 (layer thickness: 0.5 μm, Si doping: 8 × 10 ¹⁷ cm ⁻³ ), n on an (100) plane n-GaAs substrate 101. -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, Zn doped: 1 × 10 ¹⁸ cm ⁻³ ), p-Al _0.4885 Ga _0.5115 As second upper cladding sublayer 109 (thickness: 0.1 [mu] m, ^{Zn-doped: 1 × 10 17 cm -3)} , p-GaAs etching stop layer 11 (Layer thickness 30 Å, ^{Zn-doped: 2 × 10 18 cm -3)} , p-Al 0.4885 Ga 0.5115 As second upper cladding upper layer 111 (layer thickness 1.28, Zn-doped: 2.7 × 10 ¹⁸ cm ^-3 P-GaAs contact layer 112 (layer thickness: 0.2 μm, Zn doping: 3.3 × 10 ¹⁸ cm ⁻³ ), p ⁺ -GaAs contact layer 113 (layer thickness: 0.3 μm, Zn doping: 1 ×) 10 ²¹ cm ⁻³ ) are successively grown by MOCVD. The multi-strain quantum well active layer 106 includes an In _0.2655 Ga _0.7345 As _0.5914 P _0.4086 compression strain quantum well layer (strain 0.47%, layer thickness 50 _mm , two layers) and an In _0.126 Ga _0.874 As _0.4071 P _0.5929 barrier layer (strain -1.2%, 3 layers from the substrate side with a layer thickness of 90 mm, 50 mm, and 90 mm, the closest layer to the substrate being the n side barrier layer and the farthest layer being the p side barrier layer) Is formed.

  Next, in FIG. 2A, a resist mask 118 (mask width 3.5 μm) is formed in a region 119a where a ridge (mesa stripe) portion is formed by a photolithography process so that the stripe direction has a <0-11> direction.

  Next, the region 119b where the ridge portion other than the resist mask portion 118 is not formed is removed by etching to form the ridge portion 100 as shown in FIG. 2B. The etching at this time is performed in two steps 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. The depth of etching is 1.78 μm, and the width of the lowermost portion of the ridge portion 100 having a forward mesa stripe shape is about 3.2 μm. After the etching, the resist mask 118 is removed.

  Subsequently, as shown in FIG. 2C, Ti (500 Å) / Pt (500 Å) / Au (4000 Å) are stacked in this order as the p-side electrode 114 serving as the base of the upper electrode by using an electron beam evaporation method. Form.

  Thereafter, a photoresist (not shown) for defining a formation region of the bump electrode 116 (shown in FIG. 2D) is formed. The photoresist is provided so as to cover at least the chip end portion 117 (shown in FIG. 1) of the semiconductor laser element.

  Then, as shown in FIG. 2D, the thin film electrode is used as a power supply metal in the plating process, and a thick film (bump) electrode 116 made of gold having a thickness of 10 μm is formed in the photoresist opening. After the plating process, the photoresist is removed, and the upper electrode (thin film electrode + bump electrode) is removed to the extent that the gold of the uppermost layer of the thin film electrode in the region where the bump electrode 116 is not formed is removed using an iodine-based gold etchant. Etching away the gold on the surface.

Thereafter, the substrate 101 is ground from the back side to a desired thickness (about 100 μm in this case) by a lapping method, and an AuGe alloy (Au: 88%) is used as the n-side electrode 115 by using a resistance heating vapor deposition method from the back side. , Ge: 12%) is 1000 Å followed by Ni (150 Å) and Au (3000 Å). Thereafter, heating is performed at 390 ° C. for 1 minute in an N ₂ atmosphere to perform an alloying process on the electrode material. As a result, at the interface between the p-side electrode 114 and each semiconductor layer in contact with the p-side electrode 114, a compound layer (shown in FIG. 10) in which Ti and at least one of the constituent elements of each semiconductor layer are alloyed. It is formed. Thereafter, the substrate 101 is divided into bars having a desired resonator length (here, 800 μm), end face coating is performed, and the chips are further divided into chips (800 μm × 250 μm). The cleavage area for bar division and chip division is made to be the same as the gold etching area described above. Through the above steps, the semiconductor laser device according to the first embodiment of the present invention shown in FIG. 1 is completed.

  FIG. 10 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 20 to 30 mm in depth in the normal direction of the interface between the p-side electrode and the semiconductor layer. Therefore, in the second upper clad lower layer 109, a region where the forward mesastrip-shaped ridge portion 100 is not formed thereon has a thickness of about 20 to 30 mm smaller than a region immediately below the ridge portion 100.

  In the semiconductor laser device according to the first embodiment of the present invention, as shown in FIG. 3, the shortest distance in the thickness direction from the active layer to the upper electrodes (114, 116) on both sides of the striped ridge portion 100 is Hc, The height of the ridge portion 100 is Hr, the film thickness of the upper electrode (114, 116) is He, the distance from the ridge portion 100 in the direction away from the lower edge of the ridge portion 100 as a base point is x. In this case, at least in the range satisfying x ≦ (Hc + He), it is formed so as to satisfy the condition of “upper electrode film thickness He”> “ridge portion 100 height Hr”.

  The region where the heat generated from the light emitting region at the time of laser oscillation in the active layer immediately below the ridge portion 100 is effectively diffused at the interface between the upper clad layer side semiconductor layer surface and the upper electrode of this configuration is the inclined surface of the ridge portion 100. The lower edge is in a range of 0 ≦ x ≦ Hc · tan 45 ° where x = 0. Considering the thickness of the upper electrode, 0 ≦ x ≦ (Hc + He) tan 45 ° is similarly obtained on the surface of the upper electrode (from the theory of approximating 45 ° to a region effective for spreading of heat from the heating point). By forming the upper electrode thicker than the ridge portion 100 in the range of 0 ≦ x ≦ (Hc + He) tan 45 °, that is, in the range of 0 ≦ x ≦ (Hc + He) since tan 45 ° = 1, laser oscillation is achieved. Most of the heat generated sometimes can be radiated to the upper surface of the upper electrode without being radiated into the atmosphere. At this time, the heat radiation effect of the present invention is maximized by connecting a heat radiator (not shown) to the upper electrode. This is because the thermal conductivity of the atmosphere is generally smaller than 1/1000 of the thermal conductivity of metal materials (the thermal conductivity of dry air at 0 ° C. is 0.0241 W / m · K, while metal The thermal conductivity of the material is generally several 10 to 400 W / m · K).

  In general, the ridge waveguide type semiconductor laser element is exposed to a structure of the ridge portion, and therefore, when the chip is mounted on a package or wire bonding, a part of the ridge portion is easily chipped or damaged. There was a problem. Such breakage of the ridge portion is extremely undesirable because it deteriorates desired optical characteristics. However, according to the semiconductor laser device of the present invention, by providing an electrode structure having a thickness equal to or higher than the ridge height on both sides of the ridge portion 100, the thick film (bump) electrode serves as a protector for the ridge portion. It becomes possible to protect the physical damage of the ridge portion.

  In the semiconductor laser device of the present invention, the uppermost layer of the upper electrode which is a multilayer metal film is gold. This is because gold is difficult to oxidize, so that good electrical connection can be made to the outside, and since gold is softer than the materials that make up the semiconductor layer, unnecessary stress on the semiconductor layer (stress ), And may be easily connected to an external radiator by thermocompression bonding. In addition, in the semiconductor laser device of the present invention, the gold film thickness is 9/10 or more with respect to the total film thickness of the upper electrode. As a result, the heat conduction characteristics in the upper electrode can be improved. The reason for this is that the thermal conductivity of gold (for example, 319 W / m · K at 0 ° C.) is larger than most other metals. Incidentally, as metals having a higher thermal conductivity than gold, there are silver and copper (428 W / m · K and 403 W / m · K at 0 ° C., respectively), but silver has a drawback that it is easily oxidized, When copper diffuses into a semiconductor, it has a drawback of causing element deterioration. Therefore, copper is not preferred, and gold is most preferred. In the first embodiment, titanium / platinum is used as a gold base, but a metal layer having a lower thermal conductivity than gold is inserted by setting the film thickness to 1/10 or less of the total film thickness. The adverse effect of being present can be reduced.

  When the thick film (bump) electrode of the semiconductor laser element having the above-described structure is used for thermocompression bonding and connected to the heat radiator, the thickness He of the upper electrode is more preferably at least three times the height Hr of the ridge. Is preferably 5 times or more. This is because the gold in the thick film (bump) electrode is slightly crushed and joined to the heat sink during thermocompression bonding, and damage is applied to the ridge if the upper electrode thickness is not larger than the height of the ridge. . According to the examination, it was found that if He> 3Hr, the damage of the ridge portion is suppressed to about 1% or less, and if He> 5Hr, about 0.01% or less.

  In the semiconductor laser device of the first embodiment, a thick film (bump) electrode is provided directly above the ridge portion, but it is not always necessary to have a thick film (bump) electrode directly above the ridge portion. If a thick film (bump) electrode is not provided directly above the ridge, no stress is applied to the ridge when thermocompression bonding with the heat sink, reducing ridge damage or reliability during operation. Concerns are even smaller. In order not to form the thick film electrode immediately above the ridge portion, a plating resist pattern may be formed also on the flat portion directly above the ridge portion. However, as a matter of course, it is necessary to provide the thin film electrode also directly above the ridge portion for current injection.

  Further, in the semiconductor laser device of the present invention, the thickness of the upper electrode at the chip end is made smaller than the thickness of the upper electrode in other regions. As a result, cleaving at the time of bar division and chip division became smooth, and the yield was improved. Although the electrode is left at the end of the chip even though it is thin, there is an advantage that current can be easily injected near the reflection end face of the laser beam.

The semiconductor laser device in the first embodiment described above performs current confinement to the ridge portion using a Schottky junction. In the case of such a semiconductor laser element, since the upper electrode is directly formed on the semiconductor layer other than the ridge portion, the electrode structure using the heat dissipation mechanism as in the present invention is particularly effective. Of course, even in a more general air ridge structure through an insulator film (for example, silicon oxide (SiO ₂ ) or silicon nitride (SiN _x )), the heat dissipation effect can be sufficiently increased by applying the electrode structure of the present invention. Is possible.

  When current confinement is performed using a Schottky junction as described above, a compound layer (FIG. 10) is formed at the interface between the lowermost electrode material of the thin film electrode and the semiconductor layer by performing heat treatment after the thin film electrode is formed. Forming a ridge waveguide semiconductor laser device in which the Schottky junction property in the current confinement region and the ohmic junction property in the contact layer are further enhanced, and current is injected into the ridge portion with low resistance. it can.

  In the semiconductor laser device of the first embodiment, the configuration using the Ti film as the lowermost layer of the thin film electrode is exemplified, but the present invention is not limited to this. For example, various metals such as a Pt film, a Mo (molybdenum) film, and a Cr (chromium) film can be preferably used.

  In the case of a semiconductor laser element that performs current confinement using a Schottky junction, the thickness of the substrate is preferably 80 μm or more, more preferably 100 μm or more. This is because, when the voltage applied during the oscillation operation is about 2 to 5 V, if the thickness of the substrate is reduced and the distance between the upper and lower electrodes is reduced, breakdown breakdown Schottky junction is likely to occur. It is. Assuming the above operating voltage, it was found that the breakdown of the Schottky junction can be sufficiently suppressed if the substrate thickness is 80 μm or more. In consideration of long-term reliability, the thickness of the substrate is more preferably about 100 μm or more.

  As in the method of manufacturing a semiconductor laser device of the present invention, after a thin film electrode serving as a base of the upper electrode is provided on the entire surface of the upper clad side semiconductor, a thick film (bump) electrode formation portion is formed using a photolithography method. By using this method, a thick film (bump) electrode can be formed only in a necessary region, so that the semiconductor laser device structure of the present invention can be easily manufactured.

  In addition, since the thin film electrode is formed on the entire surface of the semiconductor layer surface on the upper cladding layer side, it can be diverted to a power supply metal for an electric field plating process, and when using a plating method for forming a thick film (bump) electrode, There is an advantage that it is not necessary to newly form a power supply metal.

  In addition, after forming gold or a gold alloy as the uppermost layer of the thin film electrode and further performing gold plating, the gold base metal (platinum and titanium) of the thin film electrode is used as an etching stopper to perform gold etching, so that a thick film ( The uppermost gold layer in the upper electrode region other than the (bump) electrode forming region can be easily removed. As a result, the opening operation at the time of the subsequent bar division and chip division can be carried out smoothly.

  Further, the iodine-based gold etchant used in the first embodiment damages the GaAs material, but in the present invention, the semiconductor surface remains covered with titanium and platinum as the base metals. No problems arise.

  Further, in the method of manufacturing a semiconductor laser device of the present invention, the thick film (bump) electrode made of gold is connected to the heat radiator by thermocompression bonding, so that the paste on the side surface of the chip when a paste such as indium is used. There is no problem such as a short circuit due to the bulging of the metal, and there is an advantage that a good thermal bond can be obtained because no extra substance is interposed in the electrode / heat sink interface.

  In the semiconductor laser device of the first embodiment, a GaAs semiconductor laser device using GaAs as a substrate has been described as an example. However, the present invention is not limited to this. Needless to say, the present invention can be applied to, for example, an InP semiconductor laser element or a GaN semiconductor laser element.

  In addition, the configuration of the active layer, the guide layer, the clad layer, and the like can be changed without departing from the present invention. Of course, the interface between the semiconductor layers having different material systems is not clearly shown in the first embodiment. A semiconductor layer similar to the interface protective layer may be provided. In the first embodiment, the case where the wet etching method is used for forming the ridge is disclosed, but the 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.

  In the first embodiment, the bump electrode 116 is also provided on the ridge portion. However, by forming the bump electrode after providing the resist mask on the ridge portion, the bump electrode (thickness) is formed on the ridge portion. It may not be covered with the membrane electrode). In this case, since the stress is not applied to the ridge portion when the radiator is pressure-bonded to the bump electrode, the reliability can be improved.

(Second embodiment)
FIG. 4 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 dummy ridge portions 120 are formed on both sides of the ridge portion 100.

  Hereinafter, the configuration and manufacturing method of the dummy ridge portion 120 formed on both sides of the ridge portion 100 will be described in particular, and the description of the 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 clad lower layer 109 as an example of a low-concentration semiconductor layer are sequentially stacked.

On this second upper cladding lower layer 109, a p-GaAs etching stop layer 110, a p-Al _0.4885 Ga _0.5115 As second upper cladding upper layer 111, a p-GaAs contact layer 112, and a stripe-shaped ridge portion 100, and A p ⁺ -GaAs contact layer 113 is provided as an example of the high concentration semiconductor layer.

On the other hand, in addition to the p-GaAs etching stop layer 110, the p-Al _0.4885 Ga _0.5115 As second upper cladding upper layer 111, the p-GaAs contact layer 112 and the p ⁺ -GaAs contact layer 113, the dummy ridge portion 120 is at least p ⁺ -GaAs top and p ⁺ -GaAs contact layer 113 and the insulating film 121 made of SiO ₂ having a thickness of 1000Å so as to cover the side surface portion of the p-GaAs contact layer 112 of the contact layer 113 is provided.

  Further, the top electrode of the multilayer metal film formed in the order of Ti / Pt / Au on the top of the ridge structure 100, the side surface, the upper portion of the second upper clad lower layer 109, and the surface of the dummy ridge portion 120 is formed. A p-side electrode 114 is provided as a base.

  Furthermore, a compound layer (shown in FIG. 10) in which Ti and at least one of the constituent elements of each semiconductor layer are alloyed is formed at the interface between each semiconductor layer in contact with the p-side electrode 114. A bump electrode 116 as an example of a thick film electrode made of Au is provided on the p-side electrode 114 so as to cover the ridge portion 100 and the dummy ridge portion 120. The upper surface of the bump electrode 116 becomes a mounting surface to be joined to a heat radiator (not shown) provided outside.

  On the back surface of the n-GaAs substrate 101, an Au-Ge-Ni / Au multilayer metal thin film is formed as the n-side electrode 115.

  As in the first embodiment, the bump electrode 116 has at least x ≦ (Hc + He) tan 45 when the distance in the direction away from the ridge portion 100 is x, with the lower edge of the inclined surface of the ridge portion 100 as a base point. Within a range satisfying the angle, the height satisfies the condition of He> Hr. Further, only the Ti film and the Pt film among the Ti film, the Pt film, and the Au film constituting the p-side electrode 114 are formed at the chip end portion 117 of the semiconductor laser element.

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

First, an n-GaAs buffer layer 102 (layer thickness: 0.5 μm, Si doping: 8 × 10 ¹⁷ cm ⁻³ ), n-Al _0.453 Ga _0.547 As No. on an (100) plane n-GaAs substrate 101. 1 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: 0.24 μm, Si doping: 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, Zn doped: 1 × 10 ¹⁸ cm ⁻³ ), p-Al _0.4885 Ga _0.5115 As second upper cladding lower layer 109 (layer thickness: 0.1 [mu] m, ^{Zn-doped: 1 × 10 17 cm -3)} , p-GaAs etching stop layer 110 (layer thickness 30 Å, Zn dough ^{: 2 × 10 18 cm -3)} , p-Al 0.4885 Ga 0.5115 As second upper cladding upper layer 111 (layer thickness 1.28, ^{Zn-doped: 2.7 × 10 18 cm -3)} , p-GaAs contact layer 112 (layer thickness: 0.2 μm, Zn doping: 3.3 × 10 ¹⁸ cm ⁻³ ), p ⁺ -GaAs contact layer 113 (layer thickness: 0.3 μm, Zn doping: 1 × 10 ²¹ cm ⁻³ ) Sequentially, crystals are grown by MOCVD.

  Next, a resist mask is formed at a portion where the ridge portion 100 and the dummy ridge portion 120 are formed by a photolithography process so that the stripe direction has the <0-11> direction.

  Next, portions other than the resist mask are removed by etching to form a ridge portion 100 and a dummy ridge portion 120. After the etching, the resist mask is removed.

Thereafter, a SiO ₂ film is formed on the top and side portions of the ridge portion 100, the upper portion of the second upper clad lower layer 109, and the surface of the dummy ridge portion 120 using a plasma CVD method, and then a photolithography method is used. Then, the SiO ₂ film is selectively left only on the dummy ridge portion 120.

  Subsequently, Ti (500 ビ ー ム) / Pt (500Å) / Au (4000Å) are stacked in this order as the p-side electrode 114 serving as the base of the upper electrode by using an electron beam evaporation method to form a thin film electrode.

  Next, a photoresist for defining the formation region of the bump electrode 116 is formed. The photoresist is provided so as to cover at least the chip end portion 117 (shown in FIG. 4) of the semiconductor laser element.

  Thereafter, the thin film electrode is used as a power supply metal in the plating process, and a thick film (bump) electrode 116 made of gold having a thickness of 10 μm is formed in the photoresist opening. After the plating process, the photoresist is removed, and the upper electrode (thin film electrode + bump electrode) is removed to the extent that the uppermost gold layer of the thin film electrode in the region where the bump electrode 116 is not formed is removed using an iodine-based gold etchant. ) Etch away the gold on the surface.

Subsequently, the substrate 101 is ground by a lapping method from the back surface side to a desired thickness (here, about 100 μm), and an AuGe alloy (Au: 88) is used as the n-side electrode 115 by resistance heating evaporation from the back surface side. %, Ge: 12%) is 1000 Å followed by Ni (150 Å) and Au (3000 Å). Thereafter, heating is performed at 390 ° C. for 1 minute in an N ₂ atmosphere to perform an alloying process on the electrode material. As a result, at the interface between the p-side electrode 114 and each semiconductor layer in contact with the p-side electrode 114, a compound layer in which Ti and at least one of the constituent elements of each semiconductor layer are alloyed is formed. Thereafter, the substrate 101 is divided into bars having a desired resonator length (here, 800 μm), end face coating is performed, and the chips are further divided into chips (800 μm × 250 μm). The cleavage area for bar division and chip division is made to be the same as the gold etching area described above. The semiconductor laser device according to the second embodiment of the present invention is completed through the above steps.

  In the semiconductor laser device of the second embodiment, in addition to the semiconductor laser device of the first embodiment provided with a thick film (bump) electrode having a thickness equal to or greater than the height of the ridge portion, both sides of the ridge portion 100 are further provided. Since the dummy ridge portion 120 is provided on the ridge portion, damage to the ridge portion in a later process can be further prevented. In particular, it is effective in avoiding physical damage of the ridge portion when the bump electrode 116 is thermocompression bonded to the heat radiating body, and the manufacturing yield of the semiconductor laser device can be greatly improved.

In the semiconductor laser device of the second embodiment, by forming the insulator film 121 made of the SiO ₂ film on the surface of the dummy ridge portion 120, current injection from the upper electrodes (114, 116) to the dummy ridge portion 120 is performed. It is preventing. The semiconductor layer constituting the dummy ridge portion 120 has the same composition and thickness as the ridge portion 100, but the dummy ridge portion 120 is compared to the ridge portion 100 by the amount of the insulating film 121 provided on the surface thereof. high. This can reduce damage to the ridge portion 100 particularly when the upper electrode side is thermocompression bonded to a radiator (such as a stem or submount).

Here, as the insulator film, in addition to the above-described SiO ₂ film (silicon oxide film), a thin film of an inorganic insulator such as a SiN _x film (silicon nitride film), an organic resin (for example, a polyimide resin), or the like. It can be suitably applied.

In the semiconductor laser device of the second embodiment described above, the insulator film 121 is formed on the surface of the dummy ridge portion 120 in order to avoid current injection from the upper electrode to the dummy ridge portion 120. In addition, a low-concentration semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less like the p-Al _0.4885 Ga _0.5115 As second upper cladding lower layer 109 may be provided in the uppermost layer of the dummy ridge portion. In this case, in the step of crystal growth on the n-GaAs substrate, the p ⁺ -GaAs contact layer 113 which is the uppermost layer of the ridge portion is followed by, for example, a p-Al _0.5 Ga _0.5 As current blocking layer (layer thickness: 0.00). 2 μm, Zn doping: 1 × 10 ¹⁷ cm ⁻³ ), and prior to the subsequent formation of the ridge portion and dummy ridge portion, an etching process is performed to leave the current blocking layer only on the dummy ridge portion formation region. Add it.

  With such a configuration, a good Schottky junction is formed between the current blocking layer and the upper electrode, and current confinement to the dummy ridge is realized without forming an insulator film. can do.

  As the current blocking layer, in addition to the AlGaAs semiconductor layer described above, an InGaAs semiconductor layer, an InGaAsAs semiconductor layer, or the like can be preferably used. Furthermore, these InGaP semiconductor layers and InGaAsP semiconductor layers may be formed at the interface between the upper electrode and the second upper cladding lower layer so as to cover the surface of the second upper cladding lower layer. With such a configuration, there is an effect of further strengthening current confinement between the upper electrode and the second upper cladding lower layer.

  In addition to using the Schottky junction described above, the current blocking layer is configured to block current by forming a semiconductor layer having a conductivity type opposite to the dummy ridge portion (here, n-type). It can also be used. Also in this case, as a material for forming the semiconductor layer, InGaAs or InGaAsP can be suitably used in addition to AlGaAs.

(Third embodiment)
FIG. 5 shows an example of the structure of the optical disc apparatus 200 according to the present invention. This is for writing data on the optical disc 201 or reproducing the written data. As the light emitting element used at that time, the semiconductor laser of the first or second embodiment of the present invention described above is used. An element 202 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 202 is converted into parallel light by the collimator lens 203, passes through the beam splitter 204, the polarization state is adjusted by the λ / 4 polarizing plate 205, and then the objective lens 206 The light is condensed and irradiated onto the optical disc 201.

  On the other hand, at the time of reading, the optical disc 201 is irradiated with a laser beam carrying no data signal along the same path as at the time of writing. After this laser beam is reflected by the surface of the optical disc 201 on which data is recorded, after passing through the laser beam irradiation objective lens 206 and the λ / 4 polarizing plate 205, the laser beam is reflected by the beam splitter 204 and the angle is changed by 90 °. The light is collected by the light receiving element objective lens 207 and enters the signal detecting light receiving element 208. The recorded data signal is converted into an electric signal by the intensity of the laser beam incident in the signal detecting light receiving element 208 and is reproduced by the signal light reproducing circuit 209 to the original signal.

  The optical disk apparatus according to the third embodiment can improve the output of the semiconductor laser device as compared with the conventional one by using the semiconductor laser device with improved heat dissipation characteristics and reduced manufacturing steps than before. An optical disk device capable of high-speed writing can be provided at 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.

(Fourth embodiment)
FIG. 6 is a cross-sectional view showing an optical transmission module 300 of the optical transmission system according to the fourth embodiment of the present invention. FIG. 7 is a perspective view showing a light source portion. In the fourth embodiment, an InGaAs semiconductor laser element (laser chip 301) that oscillates in the 890 nm band using the configuration and manufacturing method described in the first or second embodiment is used as a light source, and silicon is used as a light receiving element 302. A (Si) pin photodiode is used. 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. 6, a pattern of both positive and negative electrodes for driving a semiconductor laser is formed on a circuit board 306. As shown in the drawing, a recess 306a having a depth of 300 μm is provided in a portion on which a laser chip is mounted. A laser mount (mounting material) 310 as an example of a heat radiating body on which the laser chip 301 is mounted is fixed to the recess 306a with solder. At this time, the flat portion 313 of the negative electrode 312 of the laser mount 310 is electrically connected to the laser driving negative electrode portion (not shown) on the circuit board 306 by the wire 307a. The recess 306a has a depth that does not hinder the emission of laser light, and the roughness of the surface does not affect the emission angle.

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

  Next, an appropriate amount of a liquid silicon resin 309 is dropped onto a portion on which the laser mount 310 fixed to the concave portion 306a is mounted with solder. The silicon resin 309 stays in the recess 306a due to surface tension, covers the laser mount 310, and is fixed to the recess 306a. In the fourth embodiment, the recess 306a is provided on the circuit board 306 and the laser mount 310 is mounted. However, as described above, the silicon resin 309 remains on the surface of the laser chip 301 and its vicinity due to surface tension. Is not necessarily provided.

  Thereafter, it is heated at 80 ° C. for about 5 minutes to be cured until it forms a jelly. Next, it is covered with a transparent epoxy resin mold 303. A lens portion 304 for controlling the radiation angle is formed on the upper surface of the laser chip 301, and a lens portion 305 for condensing signal light is integrally formed on the upper surface of the light receiving element 302 as a molded lens.

  Next, the laser mount 310 will be described with reference to FIG. As shown in FIG. 7, a laser chip 301 is die-bonded to a L-shaped heat sink 311 by thermocompression bonding of bump electrodes (not shown). The laser chip 301 is the InGaAs-based semiconductor laser element described in the first or second embodiment, and the chip lower surface 301b is coated with a high reflection film, while the laser chip upper surface 301a is a low reflection film. Is coated. These reflective films also serve as protection for the end face of the laser chip.

  A negative electrode 312 is fixed to the base 311 b of the heat sink 311 with an insulator so as not to be electrically connected to the heat sink 311. The negative electrode 312 and the n-type electrode 301c on the surface of the laser chip 301 are connected by a gold wire 307c. As described above, the laser mount 310 is soldered to the positive electrode (not shown) of the circuit board 306 in FIG. 6, and the flat part 313 on the upper side of the negative electrode 312 and the negative electrode part (see FIG. (Not shown) with a wire 307c. By forming such wiring, the optical transmission module 300 that can obtain the laser beam 314 by oscillation is completed.

  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 300 is shown in FIG. This optical transmission system includes the above-described optical transmission module 300 in both the personal computer 315 and the base station 316 installed on the ceiling of the room, and uses it as a terminal and a server, respectively, to realize data communication using light (infrared rays). It is.

  Since the optical transmission module 300 of the fourth embodiment can be manufactured at a low cost as described above and uses a semiconductor laser element having excellent temperature characteristics and excellent heat dissipation characteristics, it is used in a wider temperature range than before. An optical transmission system that can be provided can be provided at a low price.

  The semiconductor laser device, the optical transmission system, and the optical disc apparatus 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.

FIG. 1 is a schematic sectional view of a semiconductor laser device according to a first embodiment of the present invention. FIG. 2A is a schematic cross-sectional view illustrating the manufacturing process of the semiconductor laser element. FIG. 2B is a schematic cross-sectional view illustrating the manufacturing process of the semiconductor laser element following FIG. 2A. FIG. 2C is a schematic cross-sectional view for explaining the manufacturing process of the semiconductor laser element following FIG. 2B. FIG. 2D is a schematic cross-sectional view for explaining the manufacturing process of the semiconductor laser element following FIG. 2C. FIG. 3 is a schematic diagram for explaining the upper electrode of the semiconductor laser element. FIG. 4 is a schematic sectional view of a semiconductor laser device according to the second embodiment of the present invention. FIG. 5 is a schematic diagram of an optical disc apparatus according to the third embodiment of the present invention. FIG. 6 is a schematic diagram illustrating an optical transmission module used in the optical transmission system according to the fourth embodiment of the present invention. FIG. 7 is a perspective view of a light source portion of the light transmission module. FIG. 8 is a schematic diagram showing an embodiment of an optical transmission system using the optical transmission module of the fourth embodiment. FIG. 9 is a schematic sectional view of a conventional semiconductor laser device. FIG. 10 is a schematic cross-sectional view illustrating a compound layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Ridge part 101 ... n-GaAs substrate 102 ... n-GaAs buffer layer 103 ... n-AlGaAs first lower cladding layer 104 ... n-AlGaAs second lower cladding layer 105 ... AlGaAs lower guide layer 106 ... multiple strain quantum well activity Layer 107 ... AlGaAs upper guide layer 108 ... p-AlGaAs first upper cladding layer 109 ... p-AlGaAs second upper cladding lower layer 110 ... p-GaAs etching stop layer 111 ... p-AlGaAs second upper cladding upper layer 112 ... p -GaAs contact layer 113 ... p ⁺ -GaAs contact layer 114 ... p-side electrode 115 ... n-side electrode 116 ... bump electrode 117 ... chip edge 118 ... resist mask 119a ... region for forming a ridge portion 119b ... no ridge portion formed Area 120 ... Dummy ridge 121 ... Insulator film 200 ... Optical disc device 201 ... Optical disc 2 DESCRIPTION OF SYMBOLS 02 ... Semiconductor laser element 203 ... Collimating lens 204 ... Beam splitter 205 ... (lambda) / 4 polarizing plate 206 ... Objective lens 207 ... Light receiving element objective lens 208 ... Signal detection light receiving element 209 ... Signal light reproduction circuit 300 ... Optical transmission module 301 ... Semiconductor laser element 301a ... Low reflection film 301b ... High reflection film 301c ... N-side electrode 302 ... Light receiving element 303 ... Epoxy resin mold 304 ... Lens part 305 ... Lens part 306 ... Circuit board 306a ... Recesses 307a, 307b, 307c ... Wire 308... IC circuit 309. Silicon resin 310. Laser mount 311. Heat sink 311 b. Base 312. Negative electrode 313. Layer 40 ... strained quantum well active layer 404 ... p-InGaP cladding layer 405 ... p-InGaAs contact layer 406 ... p-side electrode 407 ... n-side electrode 408 ... Schottky junction

Claims (23)

An active layer formed on a substrate of the first conductivity type and a second conductivity type semiconductor layer group formed on the active layer, and a part on the upper side of the second conductivity type semiconductor layer group Is a semiconductor laser element forming a stripe-shaped ridge portion,
An upper electrode is formed so as to cover the second conductive type semiconductor layer group including the ridge portion,
A semiconductor laser device characterized in that at least the surface of the upper electrode in a region wider than the area of the upper surface of the ridge portion is a mounting surface. The semiconductor laser device according to claim 1,
Dummy ridge portions that are part of the upper side of the second conductivity type semiconductor layer group and are higher than the height of the ridge portion are provided on both sides of the striped ridge portion,
A semiconductor laser device, wherein the upper electrode is formed so as to cover the second conductive type semiconductor layer group including the ridge portion and the dummy ridge portion. The semiconductor laser device according to claim 2,
2. The semiconductor laser device according to claim 1, wherein the dummy ridge portion includes the same semiconductor layer group as the ridge portion and an insulator film provided on a surface of the semiconductor layer group constituting the dummy ridge portion. The semiconductor laser device according to claim 2,
The semiconductor laser device, wherein the dummy ridge portion has a current blocking layer which forms a Schottky junction with the upper electrode formed thereon on the same semiconductor layer group as the ridge portion. The semiconductor laser device according to claim 2,
The dummy ridge portion has a current blocking layer made of a first conductivity type semiconductor layer on the same semiconductor layer group as the ridge portion. The semiconductor laser device according to claim 1,
The shortest distance in the thickness direction from the active layer to the upper electrode is Hc, the height in the thickness direction of the ridge is Hr, the thickness of the upper electrode on both sides of the ridge is He, When the distance in the direction parallel to the plane of the substrate and away from the ridge portion is defined as x with the lower edge of the inclined surface of the ridge portion as a base point,
At least in the range of x ≦ (Hc + He),
He> Hr
A semiconductor laser device satisfying the following conditions: The semiconductor laser device according to claim 6, wherein
A semiconductor laser element, wherein a heat radiator is connected to a region of the upper electrode that satisfies at least the condition of He> Hr. The semiconductor laser device according to claim 6, wherein
The upper electrode is a multilayer metal film,
A semiconductor laser device, wherein the uppermost layer in the region of the multilayer metal film satisfying at least the condition of He> Hr is made of gold or a gold alloy. The semiconductor laser device according to claim 8, wherein
A ratio of the film thickness of the uppermost layer made of gold or a gold alloy to the total film thickness in a region where the multilayer metal film satisfies at least the condition of He> Hr is 9/10 or more. . The semiconductor laser device according to claim 6, wherein
Within the range of x ≦ (Hc + He),
He> 3Hr
A semiconductor laser device satisfying the following conditions: The semiconductor laser device according to claim 1,
2. A semiconductor laser device according to claim 1, wherein a film thickness of a region in the vicinity of the chip end of the upper electrode is smaller than a film thickness of another region of the upper electrode. The semiconductor laser device according to claim 1,
A semiconductor laser element, wherein current confinement is performed on the ridge portion by using a Schottky junction between the upper electrode and the semiconductor layer group on both sides of the ridge portion. The semiconductor laser device according to claim 12, wherein
The second conductivity type semiconductor layer group 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.
At the interface between the upper electrode and the low-concentration semiconductor layer, a low-concentration compound layer comprising at least one constituent element of the upper electrode and at least one constituent element of the low-concentration semiconductor layer is formed,
A high-concentration compound layer comprising at least one constituent element of the upper electrode and at least one constituent element of the high-concentration semiconductor layer is formed at the interface between the upper electrode and the high-concentration semiconductor layer. A semiconductor laser device. The semiconductor laser device according to claim 13, wherein
A semiconductor laser element, wherein a second conductivity type semiconductor layer having a doping concentration of at least 1 × 10 ¹⁷ cm ⁻³ or more is formed between the low-concentration semiconductor layer and the active layer. The semiconductor laser device according to claim 13, wherein
The semiconductor laser device, wherein the high-concentration semiconductor layer is provided on the uppermost portion of the ridge portion, and the low-concentration semiconductor layer is provided on at least a region other than the uppermost portion of the ridge portion. The semiconductor laser device according to claim 12, wherein
A semiconductor laser element, wherein the substrate has a thickness of 80 μm or more. A semiconductor laser device manufacturing method for manufacturing the semiconductor laser device according to claim 1,
Forming an active layer on a substrate of a first conductivity type;
Forming a second conductivity type semiconductor layer group on the active layer;
Removing a part of the upper side of the semiconductor layer group of the second conductivity type to form a striped ridge portion;
Forming a thin film electrode so as to cover the second conductivity type semiconductor layer group including the ridge portion;
Forming a thick film electrode on at least regions on both sides of the ridge portion of the thin film electrode, and forming an upper electrode having a surface as a mounting surface by the thin film electrode and the thick film electrode A method for manufacturing a laser element. In the manufacturing method of the semiconductor laser device according to claim 17,
In the step of forming the thin film electrode, a multilayer metal film made of gold or a gold alloy is formed as the uppermost layer,
A method of manufacturing a semiconductor laser device, wherein the thin film electrode is used as a power supply metal and the thick film electrode is formed by plating. In the manufacturing method of the semiconductor laser device according to claim 17,
The thick film electrode is made of gold or a gold alloy,
A method of manufacturing a semiconductor laser device, comprising a step of thermocompression bonding a radiator to at least regions of the thick film electrodes on both sides of the ridge portion. In the manufacturing method of the semiconductor laser device according to claim 17,
In the step of forming the second conductivity type semiconductor layer group, 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 are formed on the active layer. Forming a second conductivity type semiconductor layer group composed of a high concentration semiconductor layer of
A method of manufacturing a semiconductor laser device, comprising: forming a compound layer at an interface between the thin film electrode and the second conductivity type semiconductor layer group by performing a heat treatment after the formation of the thin film electrode. In the manufacturing method of the semiconductor laser device according to claim 20,
In the step of forming the second conductivity type semiconductor layer group, a second conductivity type semiconductor layer having a doping concentration of at least 1 × 10 ¹⁷ cm ⁻³ or more between the low concentration semiconductor layer and the active layer. Forming a semiconductor laser element.   17. An optical disc apparatus using the semiconductor laser element according to claim 1. 17. An optical transmission system using the semiconductor laser device according to claim 1.

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