JP2010027942A - Semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a window structure which is effective in COD prevention without diffusing an impurity or irradiating a resonator end surface with laser light so as to expand a band gap nearby the resonator end surface in a process of manufacturing a semiconductor laser device. <P>SOLUTION: The semiconductor laser device includes a semiconductor laser element 1 which emits the laser light from one end surface 3 of a resonator, and a sub-mount material 2 on which the semiconductor laser element 1 is mounted, wherein a first region 6 of the sub-mount material 2 is made of a material having a lower coefficient of thermal expansion than that of a second region 7 to impart tensile strain to a part of the resonator end surface 3 on the light projection side of the semiconductor laser element 1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a semiconductor laser device. Specifically, the present invention relates to a technique for preventing end face deterioration of a semiconductor laser element.

  Generally, in a high-power semiconductor laser, there is a case where a sudden destruction phenomenon: COD (Catastrophic Optical Damage) due to heat generation due to light absorption occurs at the resonator end face on the laser beam emission side during high-power operation. The generation of COD hinders high output operation and high reliability. Several techniques have been proposed to prevent the occurrence of COD. As one of them, for example, by introducing a “cleaning process” of the resonator end face by plasma before the “end face coating process” for coating the resonator end face (hereinafter also simply referred to as “end face”), the resonator A technique for reducing the interface state of the end face is known. However, even if the “cleaning step” is introduced, the generation of COD cannot be sufficiently suppressed.

  Therefore, in the wafer processing process, impurities are diffused in the part corresponding to the vicinity of the cavity end face, and the quantum well is mixed, thereby expanding the band gap near the end face of the semiconductor laser and reducing the light absorption. Is proposed. However, this technique has a drawback that the manufacturing process of the semiconductor laser including the wafer processing process is complicated. In addition, since there is a process for introducing impurities, there is a drawback that long-term reliability is reduced due to point defects generated at that time. Incidentally, the “window structure” refers to a structure in which the band gap of the active layer in the vicinity of the resonator end face is expanded to reduce light absorption at the resonator end face. The “resonator end face” refers to a laser end face that is cleaved to realize a function as a resonator.

  As another technique for realizing the “window structure” described above, as a method of manufacturing a semiconductor laser using a nitride compound semiconductor containing In (indium), after forming a resonator end face of the semiconductor laser, the resonator end face A technique for expanding the bandgap by reducing the In composition in the vicinity of the end face by irradiating a laser beam on (see Patent Document 1) is known.

JP 2006-147815 A

  According to the present invention, in the manufacturing process of a semiconductor laser device, in order to enlarge the band gap in the vicinity of the cavity end face, it is possible to perform COD without diffusing impurities or irradiating the cavity end face with laser light. An object is to provide a mechanism capable of realizing a window structure effective for prevention.

  A semiconductor laser device according to the present invention includes a semiconductor laser element that emits laser light from one end face of a resonator, and a mounting body on which the semiconductor laser element is mounted, and resonance on a light emission side of the semiconductor laser element. It has a configuration in which tensile strain is applied to the end surface portion.

  In the semiconductor laser device according to the present invention, when the semiconductor laser element in which the compressive strain is generated in the active layer is mounted on the mounting body, the tensile strain applied to the resonator end surface portion on the light emitting side of the semiconductor laser element is increased. , Acting to cancel the compressive strain of the active layer. For this reason, the piezoelectric field generated inside the laser due to the compressive strain is reduced. Therefore, the band gap is enlarged at the resonator end face portion on the light emitting side of the semiconductor laser element.

  According to the present invention, in the manufacturing process of the semiconductor laser device, in order to enlarge the band gap near the cavity end face, it is not necessary to diffuse impurities or irradiate the cavity end face with laser light. A window structure effective for preventing COD can be realized.

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the technical scope of the present invention is not limited to the embodiments described below, and various modifications and improvements have been made within the scope of deriving specific effects obtained by the constituent requirements of the invention and combinations thereof. Including form.

  A semiconductor laser device according to the present invention includes a semiconductor laser element that emits laser light from one end face of a resonator, and a mounting body on which the semiconductor laser element is mounted. In general, a semiconductor laser element generates heat when laser light is emitted. For this reason, in order to efficiently release the heat generated in the semiconductor laser element to the outside, a heat sink is used as one of the components constituting the semiconductor laser device. However, there is a large difference in thermal expansion coefficient between the material constituting the heat sink and the material constituting the semiconductor laser element. For this reason, when the semiconductor laser element is directly mounted on the heat sink, warpage or the like occurs in the semiconductor laser element due to the difference in thermal length coefficient between the two.

  From such a technical background, the configuration of the semiconductor laser device includes a configuration in which an intermediate body called a submount material is interposed between the semiconductor laser element and the heat sink to relieve stress due to a difference in thermal expansion coefficient. It has been adopted. In the semiconductor laser device according to the present invention, as an example, a configuration in which a semiconductor laser element is mounted on a submount material is employed. In such a case, the submount material corresponds to the “mounting body” described above.

(First embodiment)
FIG. 1 is a schematic side view showing the configuration of the semiconductor laser device according to the first embodiment of the present invention. In FIG. 1, a semiconductor laser element 1 is mounted on a submount material 2. The lower surface of the semiconductor laser element 1 is in contact with the upper surface of the submount material 2. On the lower surface side of the semiconductor laser element 1, a pn junction active layer (not shown) serving as a light emitting layer is provided. Further, the end face 3 on the light emitting side of the semiconductor laser element 1 is arranged flush with the end face of the submount 2 in accordance with the end face of the submount material 2.

  The semiconductor laser element 1 is a so-called GaN-based semiconductor laser element using a GaN (gallium nitride) substrate, and emits blue-violet laser light. The semiconductor laser element 1 is formed in a chip shape having a rectangular shape in plan view. Although not shown, the semiconductor laser element 1 has a resonator having a stripe structure (optical resonator).

  The resonator is formed in a stripe shape on an active layer made of, for example, InGaN. Cleaved end faces (hereinafter referred to as “resonator end faces”) 3 and 4 are formed at both ends in the length direction of the resonator (hereinafter referred to as “resonator length direction”), respectively. The resonator length direction corresponds to the left-right direction in FIG. Each resonator end face 3, 4 constitutes two parallel reflecting mirrors, and the light reflectivity of one resonator end face 3 is lower than the light reflectivity of the other resonator end face 4. . For this reason, the light oscillated by repeatedly reflecting in the resonator becomes laser light and is emitted from one resonator end face 3 into the air.

  The submount material 2 is formed in a rectangular plate shape in plan view with a larger area than the semiconductor laser element 1. The submount material 2 has an element mounting region 5 on which the semiconductor laser element 1 is mounted. The element mounting area 5 of the submount material 2 includes a first area 6 corresponding to the cavity end face 3 portion on the light emitting side of the semiconductor laser element 1 in the cavity length direction, and a first area 6 excluding the first area 6. It is divided into two regions 7.

  The “light emitting side resonator end surface portion” means a portion from the light emitting side resonator end surface 3 to a predetermined dimension L. The predetermined dimension L is a dimension defined by, for example, a minimum of 1 μm and a maximum of 50 μm. The portion from the cavity facet 3 on the light emission side to the predetermined dimension L is a portion where the probability of occurrence of COD is higher than the other portions. In particular, the portion from the light emitting side resonator end face 3 to 5 μm is a portion where the probability of COD occurrence is very high. Therefore, from the viewpoint of preventing the occurrence of COD, it is desirable that the predetermined dimension L is defined as 1 μm at the minimum and 5 μm at the maximum.

  Further, in the element mounting region 5 of the submount material 2, the first region 6 is located on the resonator end surface 3 portion in plan view with respect to the resonator end surface 3 portion on the light emitting side of the semiconductor laser element 1. This refers to a partial region of the overlapping submount material 2. Specifically, it refers to a portion from the end face of the submount material 2 arranged flush with the resonator end face on the light emitting side of the semiconductor laser element 1 to a dimension L equivalent to the end face part of the resonator. The “equivalent dimension” described here refers to a dimension that is the same as the predetermined dimension or that is several μm larger than the predetermined dimension.

  The submount material 2 is configured using a plurality of types of metal materials (composite materials) having different thermal expansion coefficients. The first region 6 and the second region 7 of the submount material 2 are made of materials having different thermal expansion coefficients. The material constituting the first region 6 has a smaller thermal expansion coefficient than the material constituting the second region 7. Considering the thermal expansion coefficient of the semiconductor laser element 1 (thermal expansion coefficient in the c-axis direction = 3.2) as a reference, the thermal expansion coefficient of the first region 6 is larger than the thermal expansion coefficient of the semiconductor laser element 1. The thermal expansion coefficient of the second region 7 is small and has the same configuration as that of the semiconductor laser element 1. “Equivalent thermal expansion coefficient” means a range where the difference in thermal expansion coefficient of materials is ± 10%. As a specific metal material, the first region 6 is made of, for example, an Fe (iron) -Ni (nickel) alloy, and the second region 7 is made of, for example, AlN (aluminum nitride).

  The submount material 2 can be produced by, for example, a method in which a through hole is made in an unsintered AlN material and sintered with an Fe—Ni alloy inserted therein. Alternatively, a member made of AlN and a member made of Fe—Ni alloy may be manufactured by joining, for example, by soldering or brazing and then cutting.

  The semiconductor laser element 1 is bonded to the submount material 2 using a solder material by a junction-down method so that a portion that becomes an active layer faces the submount material 2 side. As a solder material used for joining the semiconductor laser element 1, for example, a gold tin solder material (Au80Su20 or the like) can be used.

  In the case of manufacturing the semiconductor laser device according to the first embodiment of the present invention, in the “element mounting process” in which the semiconductor laser element 1 is mounted on the submount material 2, a tin solder material used for bonding between the two is used. The solder material is melted by heating to a melting point of 280 ° C. or higher, and the solder material is adapted to both the semiconductor laser element 1 and the submount material 2. Then, the temperature is lowered to room temperature (room temperature) in a state where the semiconductor laser element 1 and the submount material 2 are aligned with each other.

  Then, due to the temperature difference between the melting point of the solder material and room temperature, a tensile strain is applied to the resonator end face 3 portion on the light emitting side of the semiconductor laser element 1. In particular, if the semiconductor laser element 1 is mounted on the submount material 2 by the junction down method, tensile strain can be effectively applied to the active layer of the semiconductor laser element 1. This tensile strain is caused by a difference in thermal expansion coefficient between the first region 6 and the second region 7 of the submount material 2. That is, the thermal expansion coefficient of the first region 6 is smaller than the thermal expansion coefficient of the semiconductor laser device 1, the thermal expansion coefficient of the second region 7 is larger than the thermal expansion coefficient of the first region 6, and the semiconductor. This is equivalent to the thermal expansion coefficient of the laser element 1. For this reason, in the process of lowering the temperature from the melting point of the solder material to room temperature, the thermal contraction of the resonator end face 3 portion on the light emitting side of the semiconductor laser element 1 is physically bonded to the first region 6 of the submount material 2. Is suppressed by. As a result, when the temperature is lowered to the room temperature level, tensile strain is constantly applied to the resonator end face 3 portion on the light emitting side of the semiconductor laser element 1.

  In general, in a blue-violet laser on a GaN substrate, InGaN that is lattice-mismatched with GaN is used for the active layer. For this reason, a piezoelectric field is generated inside the laser due to lattice strain (compression strain). Due to the piezoelectric field, the band gap wavelength is lengthened by the quantum confined Stark shift in the quantum well active layer. For example, when the In0.08GaN layer is an active layer, the amount of strain is about 0.9%.

  On the other hand, the tensile strain applied to the resonator end face 3 portion on the light emitting side due to the temperature difference acts so as to cancel the compressive strain of the InGaN active layer. For example, when using AlN with a thermal expansion coefficient = 4.5 and an Fe—Ni alloy with a thermal expansion coefficient = 2.5, if the room temperature is 25 ° C., the portion that contacts AnN and the Fe—Ni alloy are contacted. The difference in distortion amount of 0.064% occurs in the portion where For this reason, according to this structure, the compressive strain of the InGaN active layer can be reduced by 0.064% (about 7% as a ratio to the compressive strain of the active layer) at the portion in contact with the Fe—Ni alloy. . The laser element portion in contact with the first region 6 made of Fe—Ni alloy has a reduced piezo electric field and a shorter band gap wavelength than the laser element portion in contact with the second region 7 made of AlN. For this reason, a window structure in which the band gap of the active layer in the vicinity of the resonator end face is enlarged can be realized, and light absorption at the resonator end face can be reduced. As a result, it is possible to effectively prevent the generation of COD during high output operation.

  In the first embodiment, the element mounting region 5 of the submount material 2 is divided into the first region 6 and the second region 7 excluding this, and the first region 6 is heated relatively. Although the material is made of a material having a low expansion coefficient, the present invention is not limited to this. That is, in the element mounting region 5 of the submount material 2, a region corresponding to the resonator end surface 4 portion on the side opposite to the light emitting side of the semiconductor laser device 1 is defined as a “third region”. ”May be made of a low thermal expansion coefficient material as in the first region 6. By adopting such a configuration, it is possible to effectively prevent the generation of COD at both the resonator end surface on the light emitting side and the resonator end surface on the opposite side.

(Second Embodiment)
FIG. 2 is a schematic side view showing the configuration of the semiconductor laser device according to the second embodiment of the present invention. In the second embodiment, the same components as those described in the first embodiment will be described with the same reference numerals. As illustrated, the semiconductor laser element 1 is mounted on a submount material 2. In the second embodiment, the configuration (structure) of the submount material 2 is different from that in the first embodiment. That is, the submount material 2 is not composed of the composite material to which the two kinds of metal materials described above are applied, but is composed of one kind of metal material (including an alloy) having a smaller thermal expansion coefficient than that of the semiconductor laser element 1. Yes. Here, as an example, it is assumed that the submount material 2 is made of an Fe—Ni alloy.

  The element mounting region 5 of the submount material 2 is divided into a first region 6 and a second region 7 as in the first embodiment. A plurality of concave grooves 8 are formed in the second region 7, and no concave grooves 8 are formed in the first region 6. Each groove 8 is formed on the upper surface of the submount material 2 (that is, the device mounting surface to which the semiconductor laser device 1 is bonded). Further, as shown in the plan view of FIG. 3, the plurality of concave grooves 8 are formed with a width Wt equivalent to the width of the resonator of the semiconductor laser device 1. The “equivalent width” described here refers to a range of the resonator width ± 10%. For example, when the chip width Wc of the semiconductor laser element 1 is about 200 μm, the width of the resonator of the semiconductor laser element 1 is set to a width narrower than that, for example, Wt = 20 μm. Further, the plurality of concave grooves 8 are arranged periodically at regular intervals in the resonator length direction (left-right direction in FIG. 3). Each concave groove 8 is formed in an opening shape having a rectangular shape in plan view, and its longitudinal direction corresponds to the resonator width direction and its short direction corresponds to the resonator length direction. The depth dimension D1 of each concave groove 8 is set to D1 = Tsb × 0.5, for example, where the thickness of the submount material 2 is Tsb.

  When the semiconductor laser device according to the second embodiment of the present invention is manufactured, in the “element mounting process” in which the semiconductor laser element 1 is mounted on the submount material 2, a solder material, for example gold The tin solder material is heated to a melting point of 280 ° C. or higher to melt the solder material, and the solder material is made to conform to both the semiconductor laser element 1 and the submount material 2. Then, the temperature is lowered to room temperature (room temperature) in a state where the semiconductor laser element 1 and the submount material 2 are aligned with each other.

  Then, due to the temperature difference between the melting point of the solder material and room temperature, a tensile strain is applied to the resonator end face 3 portion on the light emitting side of the semiconductor laser element 1. In particular, if the semiconductor laser element 1 is mounted on the submount material 2 by the junction down method, tensile strain can be effectively applied to the active layer of the semiconductor laser element 1. This tensile strain is caused by a difference in thermal expansion coefficient between the semiconductor laser element 1 and the submount material 2. That is, the submount material 2 is made of a material having a lower thermal expansion coefficient than that of the semiconductor laser element 1. For this reason, thermal contraction of the semiconductor laser element 1 is suppressed by physical bonding with the submount material 2 in the process of lowering the temperature from the melting point of the solder material to room temperature. In this case, when focusing on the first region 6 and the second region 7 of the submount material 2, the second region 7 has lower rigidity than the first region 6 due to the presence of the plurality of concave grooves 8. . Therefore, by reducing the rigidity of the second region 7 of the submount material 2 with respect to the semiconductor laser element 1 due to the presence of the plurality of concave grooves 8, the resonator end face 3 on the light emitting side of the semiconductor laser element 1 is obtained. Tensile strain acts on the part intensively. As a result, when the temperature is lowered to the room temperature level, tensile strain is constantly applied to the resonator end face 3 portion on the light emitting side of the semiconductor laser element 1.

  Therefore, the band gap wavelength at the resonator end face 3 is shortened for the same reason as in the first embodiment (decrease in piezoelectric field, etc.). For this reason, a window structure in which the band gap of the active layer in the vicinity of the resonator end face is enlarged can be realized, and light absorption at the resonator end face can be reduced. As a result, it is possible to effectively prevent the generation of COD during high output operation. Further, in the second region 7 of the submount material 2, a plurality of concave grooves 8 are formed with a width Wt that is equal to the width of the resonator, whereby tensile strain acting on the resonator in the second region 7 is reduced. While reducing, the fall of the exhaust heat efficiency by presence of the ditch | groove 8 can be suppressed.

(Third embodiment)
FIG. 4 is a schematic side view showing the configuration of the semiconductor laser device according to the third embodiment of the present invention. In the third embodiment, the same components as those described in the first embodiment and the second embodiment will be described with the same reference numerals. As illustrated, the semiconductor laser element 1 is mounted on a submount material 2. In the third embodiment, the configuration (structure) of the submount material 2 is different from that in the first embodiment and the second embodiment. That is, the submount material 2 is not a composite material to which two kinds of metal materials are applied as in the first embodiment, but one kind of metal material (alloy) having a smaller thermal expansion coefficient than that of the semiconductor laser element 1. Is included). Here, as an example, it is assumed that the submount material 2 is made of an Fe—Ni alloy. Further, the upper surface (mounting surface on which the semiconductor laser element 1 is mounted) of the submount material 2 is not formed with the plurality of concave grooves 8 as in the second embodiment, and the surface on the opposite side. The counterbore part 9 is provided in this.

  The element mounting region 5 of the submount material 2 is divided into a first region 6 and a second region 7 as in the first embodiment. Then, the counterbore part 9 is formed in the second area 7, and the counterbore part 9 is not formed in the first area 6. For this reason, the thickness of the first region 6 is thicker than the thickness of the second region 7. As shown in the plan view of FIG. 5, the counterbore portion 9 is formed with a width Wt equivalent to the width of the resonator of the semiconductor laser device 1. Further, the counterbore part 9 is formed in a belt shape that is long and continuous along the resonator length direction (left-right direction in FIG. 5). For this reason, the longitudinal direction of the counterbore part 9 corresponds to the resonator length direction, and the short side direction corresponds to the resonator width direction. The depth dimension D2 of the counterbore part 9 is set to D2 = Tsb × 0.75, for example, when the thickness of the submount material 2 is Tsb.

  When the semiconductor laser device according to the third embodiment of the present invention is manufactured, in the “element mounting process” in which the semiconductor laser element 1 is mounted on the submount material 2, a solder material used for bonding between the two, for example, gold The tin solder material is heated to a melting point of 280 ° C. or higher to melt the solder material, and the solder material is made to conform to both the semiconductor laser element 1 and the submount material 2. Then, the temperature is lowered to room temperature (room temperature) in a state where the semiconductor laser element 1 and the submount material 2 are aligned with each other.

  Then, due to the temperature difference between the melting point of the solder material and room temperature, a tensile strain is applied to the resonator end face 3 portion on the light emitting side of the semiconductor laser element 1. In particular, if the semiconductor laser element 1 is mounted on the submount material 2 by the junction down method, tensile strain can be effectively applied to the active layer of the semiconductor laser element 1. This tensile strain is caused by a difference in thermal expansion coefficient between the semiconductor laser element 1 and the submount material 2. That is, the submount material 2 is made of a material having a lower thermal expansion coefficient than that of the semiconductor laser element 1. For this reason, thermal contraction of the semiconductor laser element 1 is suppressed by physical bonding with the submount material 2 in the process of lowering the temperature from the melting point of the solder material to room temperature. In this case, when focusing on the first region 6 and the second region 7 of the submount material 2, the second region 7 has lower rigidity than the first region 6 due to the presence of the counterbore portion 9. For this reason, the rigidity of the second region 7 of the submount material 2 is weakened by the presence of the counterbore portion 9 with respect to the semiconductor laser element 1, so that the resonator end face 3 on the light emitting side of the semiconductor laser element 1 is formed. Tensile strain acts intensively. As a result, when the temperature is lowered to the room temperature level, tensile strain is constantly applied to the resonator end face 3 portion on the light emitting side of the semiconductor laser element 1.

  Therefore, the band gap wavelength at the resonator end face 3 is shortened for the same reason as in the first embodiment (decrease in piezoelectric field, etc.). For this reason, a window structure in which the band gap of the active layer in the vicinity of the resonator end face is enlarged can be realized, and light absorption at the resonator end face can be reduced. As a result, it is possible to effectively prevent the generation of COD during high output operation. Further, in the second region 7 of the submount material 2, the counterbore portion 9 is formed with a width Wt equivalent to the width of the resonator, thereby reducing the tensile strain acting on the resonator in the second region 7. However, a reduction in exhaust heat efficiency due to the presence of the counterbore portion 9 can be suppressed.

1 is a schematic side view showing a configuration of a semiconductor laser device according to a first embodiment of the present invention. It is the side schematic diagram which shows the structure of the semiconductor laser apparatus which concerns on the 2nd Embodiment of this invention. It is a top view which shows the structure of the submount material with which the semiconductor laser apparatus which concerns on the 2nd Embodiment of this invention is provided. It is the side schematic diagram which shows the structure of the semiconductor laser apparatus which concerns on the 3rd Embodiment of this invention. It is a top view which shows the structure of the submount material with which the semiconductor laser apparatus which concerns on the 3rd Embodiment of this invention is provided.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser element, 2 ... Submount material, 3, 4 ... End face of resonator, 5 ... Element mounting area, 6 ... 1st area | region, 7 ... 2nd area | region, 8 ... Concave groove, 9 ... Counterbore part

Claims (7)

A semiconductor laser element that emits laser light from one end face of the resonator;
A mounting body on which the semiconductor laser element is mounted;
A semiconductor laser device in which tensile strain is applied to a resonator end face portion on a light emitting side of the semiconductor laser element. In the mounting body, an element mounting area on which the semiconductor laser element is mounted excludes a first area corresponding to the resonator end face portion on the light emitting side in the resonator length direction, and the first area. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is divided into a second region, and the first region is made of a material having a smaller thermal expansion coefficient than the second region. The thermal expansion coefficient of the first region is smaller than the thermal expansion coefficient of the semiconductor laser element, and the thermal expansion coefficient of the second region is equivalent to the thermal expansion coefficient of the semiconductor laser element. Semiconductor laser device. In the mounting body, an element mounting area on which the semiconductor laser element is mounted excludes a first area corresponding to the resonator end face portion on the light emitting side in the resonator length direction, and the first area. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is divided into a second region, and a plurality of concave grooves are formed in the second region. The semiconductor laser device according to claim 4, wherein the plurality of concave grooves are formed with a width equal to a width of the resonator. In the mounting body, an element mounting area on which the semiconductor laser element is mounted excludes a first area corresponding to the resonator end face portion on the light emitting side in the resonator length direction, and the first area. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is divided into second regions, and the thickness of the first region is thicker than the thickness of the second region. A counterbore portion is provided on the surface opposite to the mounting surface on which the semiconductor laser element is mounted with respect to the mounting body so that the thickness of the first region is thicker than the thickness of the second region. The semiconductor laser device according to claim 6, wherein the counterbored portion is formed with a width equal to the width of the resonator.

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