JP2004071808A - Semiconductor laser equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser equipment capable of oscillating with a basic mode as designed without coming under influence of the thermal stress on assembling. <P>SOLUTION: The semiconductor laser equipment 10 is equipped with a metallic stem 2 and a ridge type semiconductor laser chip 1 joined to one side of the stem. The ridge type semiconductor laser chip is equipped with a first electrode layer 11 joined to the stem, a first conductive type substrate 12 laminated orderly on the first electrode layer, a first conductive type first clad layer 13, an active layer 14, a second conductive type second clad layer 15 including at least a portion with two stages of a layer thickness, an insulating layer 17 for covering a portion that is relatively thin in the layer thickness between the two stages of the second clad layer, and a second electrode 18 electrically connected in a portion that is relatively thick in the layer thickness between the two stages of the second clad layer. Then, the ridge type semiconductor laser chip oscillates laser beams with a lateral basic mode. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor laser device provided with a semiconductor laser chip.
[0002]
[Prior art]
2. Description of the Related Art A semiconductor laser device for writing on an optical disk is generally constituted by arranging a semiconductor laser chip directly or indirectly on a metal stem. FIG. 9 shows a configuration example of an AlGaInP-based red high-power laser device as an example of a high-power laser for optical disk writing. The semiconductor laser device 60 includes a stem 52 made of iron or the like, and a semiconductor laser chip 51 disposed on the stem 52 via a submount 53. The submount 53 is inserted to reduce a thermal stress generated due to a difference in linear thermal expansion coefficient between the semiconductor laser chip 51 and the stem 52. For bonding between the semiconductor laser chip 51 and the submount 53 and between the submount 53 and the stem 52, a gold-tin (Au-Sn) alloy solder having a high melting point is usually used. Further, when a high output operation of several tens of mW or more is required, such as for writing on an optical disk, it is necessary to suppress a rise in the temperature of the laser emission region 54. For this purpose, as shown in FIG. 10, the waveguide portion 65 continuous with the laser emission region 54 on the end face is mounted on the submount 53 so as to have a distance shorter than の of the entire thickness of the semiconductor laser chip 51. Join. Such a structure of the semiconductor laser chip 51 and the submount 53 is called a so-called junction down structure.
[0003]
FIG. 10 is an enlarged view of the semiconductor laser chip 51 of FIG. The semiconductor laser chip 51 includes an n-type (hereinafter abbreviated as n −) GaAs substrate 62, an n-AlGaInP clad layer 63, and a multiple quantum well (MQW) active layer 64, which are sequentially stacked on one surface of an n-side electrode 61. , A p-type (hereinafter abbreviated as p −) AlGaInP cladding layer 65, a p-GaAs contact layer 66, a SiN insulating film 67, and a p-side electrode 68. The p-AlGaInP cladding layer 65 has a stripe-shaped projection 64. In the SiN insulating film 67 covering the cladding layer 65, a hole is formed to allow current to flow only in the stripe-shaped convex portion 64. The p-side electrode 68 is formed of a metal for ohmic contact and a gold (Au) plating layer. Note that a high-melting Au-Sn-based alloy solder 55 is used to bond the semiconductor laser chip 51 to the submount 52 by die bonding.
[0004]
By the way, for optical disc applications, it is necessary to focus laser light on a small spot. In order to converge on such a small spot, it is necessary to oscillate the laser beam in the transverse fundamental mode. In the semiconductor laser device 60 shown in FIGS. 9 and 10, the laser beam is confined in the direction perpendicular to the optical axis and parallel to the active layer 64, that is, in the so-called left-right direction, and guided within the range of the stripe width W. That is, the difference (Δn = n1−n2) between the vertical equivalent refractive index (n1) of the stripe-shaped protrusion 70 and the vertical equivalent refractive index (n2) on both sides of the stripe-shaped protrusion 70 is determined. Value. As a result, the laser light is confined and guided within the range of the stripe width W corresponding to the stripe-shaped protrusion 70.
[0005]
In the three-layer stripe waveguide including the n-AlGaInP cladding layer 63, the multiple quantum well active layer 64, and the p-AlGaInP cladding layer 65, in order to oscillate laser light from the laser emission region 54 of the active layer 64 in a fundamental mode. Needs to satisfy the cutoff condition of the higher-order mode in FIG. The refractive indexes of the three layers are n2, n1, and n2, respectively. In FIG. 11, a solid line shows a cutoff curve of a higher-order mode when the stripe width W and the thickness d of the p-AlGaInP clad layer 9 on both sides of the stripe-shaped protrusion 64 are used as parameters. A region where the thickness of the cladding layer 65 is thicker than the cutoff curve is a region where only the fundamental mode is allowed. In order to cause the laser light to oscillate in the fundamental mode, for example, as shown in FIG. 11, the design point is set to a range in which the fundamental mode oscillates above the cutoff curve.
[0006]
[Problems to be solved by the invention]
In the semiconductor laser device 60, the solder 55 reacts with the electrode 68 of the semiconductor laser chip 51 during die bonding when the semiconductor laser chip 51 is assembled on the stem 52. This reaction causes an assembly stress due to thermal stress, and the assembly stress shifts the cutoff condition of the higher-order mode. Therefore, the preset design point deviates from the cutoff condition, and the fundamental mode cannot be oscillated.
[0007]
First, a mechanism in which the p-side electrode 68 reacts with the solder 55 to generate thermal stress will be described with reference to FIGS. FIG. 12 is a binary phase diagram of a gold-tin alloy at atmospheric pressure, and FIG. 13 is an enlarged view of the vicinity of the eutectic composition (Au: Sn = 71: 29) in FIG. In the semiconductor laser device 60, as described above, a gold-based material is used for the p-side electrode 18, and a high melting point gold-tin alloy-based eutectic solder (Au: Sn = 71: 29) is used for the solder 5. In this case, when the semiconductor laser chip 51 is die-bonded to the submount, when the temperature of the solder 55 having the eutectic composition is increased, the liquid phase becomes a liquid phase at the eutectic point A in FIG. On the other hand, since gold is excessive at the interface between the p-side electrode 68 and the solder 55, as shown in FIG. 13, gold is taken into the liquid-phase solder 55 from the p-side electrode 68 and the composition is gold: The transition from the point B of tin = 7: 3 to the composition C on the gold-rich side occurs, and thereafter, a solid phase ζ phase and β phase are generated. For this reason, at the die bonding temperature of about 350 ° C., almost all of the p-side electrode 68 often changes to the ζ phase or the β phase. At higher temperatures, the path from point D to point E is followed. As described above, when assembling the semiconductor laser device 60, the laser light emitting region 54 relatively close to the bonding surface is formed by the heat treatment process at the time of bonding using the solder 55 for die bonding the semiconductor laser chip 51 and the submount 53. The nearby waveguide portion 65 is susceptible to thermal stress.
[0008]
Next, a mechanism for shifting the cutoff condition of the higher-order mode will be described with reference to FIG. As shown in FIG. 9, the semiconductor laser device 60 employs a structure in which the surface (epitaxial surface side) of the semiconductor laser chip 51 near the laser emission region 4 is not flat. The linear thermal expansion coefficient (1.5 × 10 ^{−5 of} gold) of the metal used for the p-side electrode 68 is the linear thermal expansion coefficient of the semiconductor of other members (5.7 × 10 ^{−6 of} GaAs). ), Submount (4.4 × 10 ^{−6 in} AlN) and the like. Therefore, when the p-side electrode 68 shifts to the ζ phase or β phase of the gold-tin alloy at the time of die bonding as described above, a large tensile stress is generated in the stripe-shaped protrusion 70. On the other hand, compressive stress is generated in the regions on both sides of the stripe-shaped protrusion 70. Generally, when a tensile stress is applied to a semiconductor, the refractive index increases, and when a compressive stress is applied, the refractive index decreases. Therefore, when the semiconductor laser device 60 is assembled with the junction down structure as shown in FIG. 9 or FIG. 10, Δn becomes larger than the design value, and the cutoff curve shifts upward as shown by the broken line in FIG. . This shift amount varies depending on the solder 55 used and the thermal stress applied during assembly. However, in the case of a junction down structure, the cutoff curve always moves upward. When the shift amount is large, there is a problem that the design point interrupts the cutoff condition as shown in FIG. 11 and oscillation in the basic mode becomes impossible. Further, even when the shift amount is small and the design point satisfies the cut-off condition, the temperature of the stripe-shaped protrusion 70 and the laser emission region 54 further increases during high-power operation, so that Δn is smaller than the design value. (The cutoff condition moves upward on the graph). For this reason, there is a problem that the cut-off condition is interrupted and the oscillation in the basic mode becomes impossible.
[0009]
Therefore, an object of the present invention is to provide a semiconductor laser device that can oscillate in a fundamental mode as designed without being affected by thermal stress during assembly. Another object of the present invention is to provide a semiconductor laser device that can oscillate in a fundamental mode even during a high-power operation.
[0010]
[Means for Solving the Problems]
A semiconductor laser device according to the present invention, a metal stem,
A ridge-type semiconductor laser chip bonded to one surface of the stem,
The ridge type semiconductor laser chip includes a first electrode layer bonded to the stem, a first conductivity type substrate sequentially stacked on the first electrode layer, and a first conductivity type first clad. A layer, an active layer, a second cladding layer of a second conductivity type having at least a layer having a two-stage thickness, and a portion having a relatively thin layer of the two-stage portion of the second clad. An insulating layer; and a second electrode electrically connected to a relatively thick portion of the two-step portion of the second cladding layer, and oscillates a transverse fundamental mode laser beam. It is characterized by the following.
[0011]
Further, the semiconductor laser device of the present invention is the semiconductor laser device, wherein a submount is interposed between the stem and the ridge-type semiconductor laser chip.
[0012]
Further, the semiconductor laser device of the present invention is the semiconductor laser device, wherein the second electrode of the semiconductor laser chip has a layer thickness of 1 μm or more.
[0013]
Still further, the semiconductor laser device of the present invention is the semiconductor laser device, wherein the ridge-type semiconductor laser chip is made of an AlGaInP-based material.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
A semiconductor laser device according to an embodiment of the present invention will be described with reference to the accompanying drawings. In the drawings, substantially the same members are denoted by the same reference numerals.
[0015]
Embodiment 1 FIG.
First Embodiment A semiconductor laser device according to a first embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, the semiconductor laser device 10 is configured by die-bonding a ridge-type semiconductor laser chip 1 having a stripe-shaped convex portion onto a stem 2. In addition, the semiconductor laser chip 1 has a so-called junction-up structure in which the laser emission region 4 is relatively far from the joint surface with the stem 2. In this semiconductor laser device, the semiconductor laser chip has a waveguide structure which is easily affected by stress, which is a stripe-shaped convex portion 20. However, when assembling into the semiconductor laser device 10, the laser stress is generated in the lower part of the semiconductor laser chip 1 due to the difference in linear thermal expansion coefficient between the materials at the time of die bonding because the laser emission region 4 is far from the bonding surface. it can. Therefore, the thermal stress does not affect the waveguide located near the laser emission region 4. Therefore, the semiconductor laser device 10 can be oscillated in the fundamental mode as designed without being affected by thermal stress at the time of assembling. Furthermore, the effect of thermal stress can be similarly suppressed at the time of high-output operation, so that oscillation can be performed in the basic mode. Further, since the semiconductor laser chip 1 is die-bonded directly on the stem 3, no structure that causes an increase in thermal resistance is interposed, so that the thermal resistance of the semiconductor laser device 10 can be reduced. Therefore, the semiconductor laser device 10 can be used as a high-output laser device for writing on an optical disk.
[0016]
In the semiconductor laser device 10, the semiconductor laser chip 1 is joined onto the stem 2 so as to have a junction-up structure. Therefore, when Au-Sn high melting point solder is used for the solder 5 and a gold-based electrode such as gold plating is used for the n-side electrode 11, the solder 5 and the n-side electrode 11 react. Therefore, in the vicinity of the n-side electrode 11, thermal stress occurs due to the solid phase precipitated on the high temperature side. However, since the junction-up structure is employed, the waveguide portion 14 and the stripe-shaped convex portion 20 which are continuous with the laser emission region 4 on the end face have a total thickness of the semiconductor laser chip 1 from the joint surface with the stem 2. Farther than 1/2 of. Therefore, it is not affected by the thermal stress.
[0017]
In addition, iron (Fe), copper tungsten alloy (CuW), or the like can be used for the stem 2. Solder 5 is used for bonding between the semiconductor laser chip 1 and the stem 3. As the solder 5, for example, a high melting point Au-Sn alloy solder may be used.
[0018]
The semiconductor laser chip 1 constituting this semiconductor laser device will be described with reference to FIG. FIG. 2 is an enlarged view of the semiconductor laser chip 1 constituting the semiconductor laser device 10 of FIG. The semiconductor laser chip 1 includes an n-GaAs substrate 12, an n-AlGaInP cladding layer 13, a multiple quantum well (MQW) active layer 14, a p-AlGaInP cladding layer 15, A GaAs contact layer 16, a SiN insulating film 17, and a p-side electrode 18; The multiple quantum well active layer 14 includes an InGa well layer, an AlGaInP barrier layer, and an AlGaInP barrier layer (all not shown). Further, the p-AlGaInP cladding layer 15 has at least two levels of thickness, and a stripe-shaped projection 20 is formed by a relatively thick layer of the two levels. The p-AlGaInP cladding layer 15 including the stripe-shaped protrusions 20 is easily affected by stress in structure. Further, the active layer 14 corresponding to the stripe-shaped projections 20 has the laser emission region 4 on the end face. Further, in the SiN insulating film 17 covering the relatively thin portion of the two-stage portion of the n-AlGaInP cladding layer 15, the current is applied only to the relatively thick stripe-shaped convex portion 20. A hole has been drilled to drain the water. The p-side electrode 18 is formed of a metal for ohmic contact and a gold (Au) plating layer.
[0019]
The semiconductor laser chip 1 is made of an AlGaInP-based material. In this case, the combination of the width W of the stripe-shaped protrusion 20 and the thickness d of the p-AlGaInP cladding layer 15 on both sides of the protrusion 20 is appropriately adjusted so as to satisfy the cutoff condition of the higher-order mode shown in FIG. By selecting this, laser light in the transverse fundamental mode can be oscillated.
[0020]
Embodiment 2 FIG.
Second Embodiment A semiconductor laser device according to a second embodiment of the present invention will be described with reference to FIGS. Compared with the semiconductor laser device according to the first embodiment, this semiconductor laser device does not directly die-bond the semiconductor laser chip 1 to the stem 2 but interposes the semiconductor laser chip 1 with the stem 2 as shown in FIG. It is different in that the submount 3 is die-bonded. The submount 3 is inserted to reduce thermal stress generated by a difference in linear thermal expansion coefficient between the semiconductor laser chip 1 and the stem 3. For this submount 3, silicon carbide (SiC) or aluminum nitride (AlN) is used. By interposing the submount 3 between the stem 2 and the semiconductor laser chip 1, thermal stress caused by a difference in linear thermal expansion coefficient between materials can be reduced.
[0021]
In the semiconductor laser device 10, similarly to the semiconductor laser device according to the first embodiment, a so-called junction in which the laser emission region 4 of the semiconductor laser chip 1 is set relatively far from the joint surface with the submount 2. It adopts an up structure. Therefore, the thermal stress caused by the difference in linear thermal expansion coefficient between the materials generated at the time of die bonding is absorbed in the lower part of the semiconductor laser chip 1, and the thermal stress does not affect the waveguide located near the laser emission region 4. Therefore, oscillation can be performed in the fundamental mode as designed without being affected by thermal stress during assembly. Further, the influence of thermal stress can be suppressed even during high-power operation, so that a semiconductor laser device oscillating in the fundamental mode can be obtained.
[0022]
Embodiment 3 FIG.
Third Embodiment A semiconductor laser device according to a third embodiment of the present invention will be described with reference to FIGS. Compared with the semiconductor laser device according to the first embodiment, the semiconductor laser device 10 has a p-side electrode 18a on the upper surface of the semiconductor laser chip 1 having a layer thickness of 1 μm or more, preferably 2 to 5 μm, as shown in FIG. The difference is that a thick film electrode is used. By setting the layer thickness of the thick-film electrode to 1 μm or more, the heat dissipation can be further improved.
[0023]
Embodiment 4 FIG.
Fourth Embodiment A semiconductor laser device according to a fourth embodiment of the present invention will be described with reference to FIGS. Compared with the semiconductor laser device according to the second embodiment, the semiconductor laser device 10 has a p-side electrode 18a on the upper surface of the semiconductor laser chip 1 having a layer thickness of 1 μm or more, preferably 2 to 5 μm, as shown in FIG. The difference is that a thick film electrode is used. By setting the layer thickness of the thick-film electrode to 1 μm or more, the heat dissipation can be further improved.
[0024]
【The invention's effect】
According to the semiconductor laser device of the present invention, the semiconductor laser chip has a so-called junction-up structure in which the laser emission region of the semiconductor laser chip is relatively far from the joint surface with the stem. In addition, the width W of the relatively thick portion of the second cladding layer and the thickness d of the layer on both sides of the thick portion are designed under the oscillation conditions of the transverse fundamental mode laser beam. On the other hand, this semiconductor laser device has a waveguide structure that is easily affected by stress, which is a stripe-shaped protrusion in the semiconductor laser chip. However, when assembling into a semiconductor laser device, since the laser emission region is far from the bonding surface, thermal stress caused by a difference in linear thermal expansion coefficient between materials at the time of die bonding can be absorbed in the lower portion of the semiconductor laser chip. Therefore, the thermal stress does not affect the waveguide located near the laser emission region. Therefore, the semiconductor laser device can be oscillated in the fundamental mode as designed without being affected by the thermal stress at the time of assembling the semiconductor laser device. Furthermore, the influence of thermal stress can be suppressed even during high-power operation, so that a semiconductor laser device that oscillates in the fundamental mode can be obtained.
[0025]
According to the semiconductor laser device of the present invention, the semiconductor laser chip is not die-bonded directly to the stem, but is die-bonded to the submount inserted between the semiconductor laser chip and the stem. By inserting the submount between the submount and the stem, thermal stress caused by a difference in linear thermal expansion coefficient between materials can be reduced.
[0026]
According to the semiconductor laser device of the present invention, the second electrode on the upper surface of the semiconductor laser chip is a thick film electrode having a layer thickness of 1 μm or more. By setting the layer thickness of the thick-film electrode to 1 μm or more, the heat dissipation can be further improved.
[0027]
Furthermore, according to the semiconductor laser device of the present invention, a ridge-type semiconductor laser chip made of an AlGaInP-based material is used. In this case, by appropriately selecting the combination of the width W of the stripe-shaped protrusion and the thickness d of the p-AlGaInP clad layer on both sides of the protrusion so as to satisfy the cutoff condition of the higher-order mode, Mode laser light can be oscillated.
[Brief description of the drawings]
FIG. 1 is a side view of a semiconductor laser device according to a first embodiment of the present invention.
FIG. 2 is an enlarged side view of a semiconductor laser chip in the semiconductor laser device of FIG.
FIG. 3 is a side view of a semiconductor laser device according to a second embodiment of the present invention.
FIG. 4 is an enlarged side view of a semiconductor laser chip in the semiconductor laser device of FIG. 3;
FIG. 5 is a side view of a semiconductor laser device according to a third embodiment of the present invention.
6 is an enlarged side view of a semiconductor laser chip in the semiconductor laser device of FIG.
FIG. 7 is a side view of a semiconductor laser device according to a fourth embodiment of the present invention.
FIG. 8 is an enlarged side view of a semiconductor laser chip in the semiconductor laser device of FIG. 7;
FIG. 9 is a side view of a conventional semiconductor laser device.
FIG. 10 is an enlarged side view of a semiconductor laser chip in the semiconductor laser device of FIG. 9;
FIG. 11 is a graph showing the relationship between the oscillation mode and the width W of the protrusion of the semiconductor laser chip having the stripe-shaped protrusion, the thickness d of the cladding layer on both sides of the protrusion, and the oscillation mode.
FIG. 12 is a binary phase diagram of an Au—Sn alloy under atmospheric pressure.
13 is a schematic diagram showing an example of a temperature history of an Au—Sn alloy having a eutectic point composition (Au 71%, Sn 29%) in the binary phase diagram of FIG.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 semiconductor laser chip, 2 stem, 3 submount, 4 laser emission region, 5 solder, 10 semiconductor laser device, 11 n-side electrode, 12 n-GaAs substrate, 13 n-AlGaInP cladding layer, 14 multiple quantum well active layer, 15 p-AlGaInP cladding layer, 16 p-GaAs contact layer, 17 SiN insulating film, 18 p-side electrode, 20 protrusion, 51 semiconductor laser chip, 52 stem, 53 submount, 54 laser emission region, 55 solder, 60 semiconductor Laser device, 61 n-side electrode, 62 n-GaAs substrate, 63 n-AlGaInP cladding layer, 64 multiple quantum well active layer, 65 p-AlGaInP cladding layer, 66 p-GaAs contact layer, 67 SiN insulating film, 68 p side Electrode, 70 convex

Claims (4)

A metal stem,
A ridge-type semiconductor laser chip bonded to one surface of the stem,
The ridge type semiconductor laser chip includes a first electrode layer bonded to the stem, a first conductivity type substrate sequentially stacked on the first electrode layer, and a first conductivity type first clad. A layer, an active layer, a second cladding layer of a second conductivity type having at least a portion having a two-stage thickness, and a portion having a relatively small layer thickness among the two-stage portions of the second clad. An insulating layer; and a second electrode electrically connected to a relatively thick portion of the two-step portion of the second cladding layer, and oscillates a laser beam in a transverse fundamental mode. A semiconductor laser device characterized by the above-mentioned. 2. The semiconductor laser device according to claim 1, wherein a submount is interposed between the stem and the ridge type semiconductor laser chip. The semiconductor laser device according to claim 1, wherein the second electrode of the semiconductor laser chip has a layer thickness of 1 μm or more. The semiconductor laser device according to claim 1, wherein the ridge-type semiconductor laser chip is made of an AlGaInP-based material.

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