JP5565402B2 - Optical module, nitride semiconductor laser device, submount - Google Patents

Description

  The present invention relates to an optical module, a nitride semiconductor laser device, and a submount.

  Patent Document 1 discloses a semiconductor laser device. This semiconductor laser device includes an LD chip, a submount, and a high heat conduction stem. A submount is disposed between the LD chip and the stem.

JP 2004-214441 A

  In Patent Document 1, the high thermal conduction stem is joined to the high thermal conduction stem side surface of the submount by a joining resin. The bonding resin bonds a submount made of silicon carbide, aluminum nitride, or the like to a high heat conduction stem made of copper or the like and plated with gold. The bonding resin preferably has a high thermal conductivity, but the heat generated in the LD active layer spreads in the submount, so even if a resin having a lower thermal conductivity than the solder material is used, heat dissipation There is not much impact on the. Patent Document 1 discloses that the submount is made of silicon carbide, aluminum nitride, or the like.

  Next, the relationship between the semiconductor laser and the submount will be described using a green semiconductor laser made of a gallium nitride semiconductor as an example. The green semiconductor laser uses a semipolar main surface of a gallium nitride based semiconductor substrate. When the semipolar main surface is used, the thermal expansion coefficient on the front surface and the back surface of the gallium nitride based semiconductor substrate exhibits anisotropy. For this reason, a submount having an isotropic thermal expansion coefficient has a thermal expansion coefficient of a semiconductor laser in either direction of a thermal expansion coefficient in a direction parallel to the laser waveguide and a thermal expansion coefficient in a direction perpendicular to the laser waveguide. It will be different from the expansion coefficient.

  Available submount materials are, for example, silicon carbide and aluminum nitride, which are made of polycrystals. For this reason, the submount of Patent Document 1 does not have an anisotropic thermal expansion coefficient. Further, the material of the submount is not limited to SiC and AlN, for example, and there is diamond, and this diamond is also made of polycrystal. A blue semiconductor laser made of a gallium nitride semiconductor is manufactured using a c-plane sapphire substrate, a c-plane SiC substrate, a c-plane GaN substrate, and the like. These c-plane substrates have isotropic thermal expansion coefficients. Therefore, it is preferable to use a submount having an isotropic thermal expansion coefficient for a blue semiconductor laser having an isotropic thermal expansion coefficient.

  The present invention has been made in view of such circumstances, and a group III nitride semiconductor laser using a substrate main surface inclined with respect to a first reference plane orthogonal to the c-axis of a gallium nitride semiconductor and a sub The purpose of the present invention is to provide an optical module capable of reducing the characteristic variation of a group III nitride semiconductor laser related to the difference in thermal expansion coefficient from the mount and the anisotropy of the thermal expansion coefficient. An object of the present invention is to provide a semiconductor laser device, and to provide a submount for a group III nitride semiconductor laser.

  An optical module according to the present invention includes: (a) a submount including a hexagonal gallium nitride single crystal base having a semipolar or nonpolar main surface and having a mounting surface; and on the mounting surface of the submount. A nitride semiconductor laser device including a provided group III nitride semiconductor laser; and (b) a stem on which the nitride semiconductor laser device is mounted. The group III nitride semiconductor laser includes a substrate having a main surface made of a hexagonal gallium nitride semiconductor, an epitaxial semiconductor stack including an active layer provided on the main surface of the substrate, and the epitaxial semiconductor stack The main surface of the substrate is inclined with respect to a first reference plane orthogonal to the c-axis of the gallium nitride semiconductor, and the oscillation of the group III nitride semiconductor laser The wavelength is in the range of 400 nm to 550 nm.

  According to this optical module, the main surface of the substrate of the group III nitride semiconductor laser is inclined with respect to a reference plane perpendicular to the c-axis of the gallium nitride semiconductor of the substrate. Anisotropy with respect to thermal expansion coefficient. The group III nitride semiconductor laser is provided on a mounting surface of a submount including a hexagonal gallium nitride single crystal base having a semipolar or nonpolar main surface. The main surface of the gallium nitride single crystal base has anisotropy with respect to the coefficient of thermal expansion. Therefore, a group III nitride semiconductor laser exhibiting an anisotropic thermal expansion coefficient can be mounted on a mounting surface of a submount including a gallium nitride single crystal base exhibiting an anisotropic thermal expansion coefficient. Further, the thermal expansion coefficient of the group III nitride semiconductor laser can be close to the thermal expansion coefficient of the submount.

  A nitride semiconductor laser device according to the present invention includes (a) a submount including a gallium nitride single crystal base having a semipolar or nonpolar main surface and having a mounting surface; and (b) the mounting surface of the submount. And a group III nitride semiconductor laser provided on the top. The group III nitride semiconductor laser includes a substrate having a main surface made of a group III gallium nitride based semiconductor, and an epitaxial semiconductor stack including an active layer provided on the main surface of the substrate, The main surface is inclined with respect to a reference plane orthogonal to the c-axis of the gallium nitride semiconductor, and the oscillation wavelength of the group III nitride semiconductor laser is in the range of 400 nm to 550 nm.

  According to this nitride semiconductor laser device, the main surface of the substrate of the group III nitride semiconductor laser is inclined with respect to the first reference plane orthogonal to the c-axis of the gallium nitride semiconductor of the substrate. The substrate of the semiconductor laser has anisotropy with respect to the thermal expansion coefficient. The group III nitride semiconductor laser is provided on a mounting surface of a submount including a hexagonal gallium nitride single crystal base having a semipolar or nonpolar main surface. The main surface of the gallium nitride single crystal base has anisotropy with respect to the coefficient of thermal expansion. Therefore, a group III nitride semiconductor laser exhibiting an anisotropic thermal expansion coefficient can be mounted on a mounting surface of a submount including a gallium nitride single crystal base exhibiting an anisotropic thermal expansion coefficient. Regarding the thermal expansion coefficient as a material, the thermal expansion coefficient of the group III nitride semiconductor laser is close to the thermal expansion coefficient of the submount.

  In the optical module and the nitride semiconductor laser device according to the present invention, the epitaxial semiconductor stack includes a p-type gallium nitride based semiconductor layer in contact with the electrode, and the main surface of the substrate is the first reference surface. It is preferable to incline at an angle of 10 degrees or more.

  According to this optical module and nitride semiconductor laser device, since the epitaxial semiconductor stack is provided on the main surface of the substrate, the bonding surface between the electrode and the p-type gallium nitride based semiconductor layer is Tilt at an angle.

  A submount including a hexagonal gallium nitride single crystal base having a semipolar or nonpolar main surface and having a mounting surface can reduce the above-described thermal deterioration and thermal fluctuation.

  In the optical module and the nitride semiconductor laser device according to the present invention, an angle formed between the c-axis of the gallium nitride semiconductor of the substrate and the c-axis of the gallium nitride single crystal base of the submount is within 45 degrees. Is preferred.

  According to this optical module and nitride semiconductor laser device, the angle between the c-axis of the gallium nitride semiconductor of the substrate and the c-axis of the gallium nitride single crystal base of the submount is within 45 degrees. The inclination of the c-axis of the semiconductor can be close to the inclination of the c-axis of the gallium nitride single crystal base.

  In the optical module and the nitride semiconductor laser device according to the present invention, the group III nitride semiconductor laser can be mounted on the mounting surface of the submount in an epi-down configuration.

  According to this optical module and nitride semiconductor laser device, if a submount made of a material different from that of a gallium nitride semiconductor is used, the difference in thermal expansion coefficient between the submount material and the group III nitride semiconductor laser is This causes the group III nitride semiconductor laser electrode to receive thermal stress during mounting. However, since the submount includes the gallium nitride single crystal base and has an anisotropic thermal expansion coefficient, the thermal stress during mounting can be reduced. For this reason, the thermal deterioration of an electrode can be reduced.

  The optical module and the nitride semiconductor laser device according to the present invention may further include a conductive adhesive member for mounting the group III nitride semiconductor laser on the mounting surface of the submount.

  According to this optical module and nitride semiconductor laser device, heat is applied to the group III nitride semiconductor laser during mounting using the conductive adhesive member, but thermal degradation due to thermal stress is caused by the group III nitride semiconductor laser. It is possible to reduce the occurrence in the electrode.

  In the optical module and the nitride semiconductor laser device according to the present invention, the group III nitride semiconductor laser preferably has an oscillation wavelength in the range of 480 nm to 540 nm.

  According to this optical module and nitride semiconductor laser device, the group III nitride semiconductor laser can provide laser oscillation within the above wavelength range indicating light of green and its adjacent color.

  In the optical module and the nitride semiconductor laser device according to the present invention, the group III nitride semiconductor laser preferably has an oscillation wavelength in the range of 510 nm or more and 540 nm or less.

  According to this optical module and nitride semiconductor laser device, the group III nitride semiconductor laser can provide laser oscillation within the above wavelength range showing green light.

  In the optical module and the nitride semiconductor laser device according to the present invention, it is preferable that the c-axis of the gallium nitride semiconductor of the substrate is inclined in the direction of the a-axis or m-axis of the group III nitride semiconductor.

  According to the optical module and the nitride semiconductor laser device, when the group III nitride semiconductor laser is manufactured using a c-axis substrate inclined in the a-axis or m-axis direction, the group III nitride semiconductor laser is Has an anisotropic coefficient of thermal expansion.

  In the optical module and the nitride semiconductor laser device according to the present invention, the epitaxial semiconductor stack includes a light guide layer, the light guide layer is in contact with the active layer, and an interface between the active layer and the light guide layer Can be inclined at an angle ALPHA from the c-plane orthogonal to the c-axis of the gallium nitride semiconductor.

  According to this optical module and nitride semiconductor laser device, when the interface between the active layer and the optical guide layer forms an inclination of an angle ALPHA greater than zero from the c plane perpendicular to the c axis of the gallium nitride semiconductor, the group III In a nitride semiconductor laser, the angle ALPHA defines the plane orientation of the active layer.

  In the optical module and the nitride semiconductor laser device according to the present invention, it is preferable that the angle ALPHA is in a range of not less than 63 degrees and less than 80 degrees.

  According to this optical module and nitride semiconductor laser device, when the angle ALPHA is in the range of not less than 63 degrees and less than 80 degrees, it is suitable for producing a group III nitride semiconductor laser that generates light of green and its adjacent wavelength. .

  In the optical module and the nitride semiconductor laser device according to the present invention, it is preferable that the main surface of the submount is inclined at an angle of 10 degrees or more from the c-plane of the gallium nitride single crystal base.

  According to this optical module and nitride semiconductor laser device, when the submount main surface is inclined from the c-plane at an angle of 10 degrees or more, it is suitable for providing an anisotropic thermal expansion coefficient to the submount.

  In the optical module and the nitride semiconductor laser device according to the present invention, it is preferable that the main surface of the submount is inclined at an angle of 80 degrees or more from the c-plane of the gallium nitride single crystal base.

  According to this optical module and nitride semiconductor laser device, when the submount main surface is inclined from the c-plane at an angle of 80 degrees or more, the anisotropic thermal expansion coefficient close to the nonpolar surface of gallium nitride is applied to the submount. It is suitable for providing.

  In the optical module and the nitride semiconductor laser device according to the present invention, the mounting surface includes a first submount thermal expansion coefficient related to a first in-plane direction along the mounting surface, and a second in-plane direction along the mounting surface. A second submount thermal expansion coefficient with respect to a direction, wherein the first in-plane direction is orthogonal to the second in-plane direction, and the first submount thermal expansion coefficient of the submount is the first submount thermal expansion coefficient of the submount. The group III nitride semiconductor laser has a first element thermal expansion coefficient with respect to the first in-plane direction and a second element thermal expansion coefficient with respect to the second in-plane direction. The first thermal expansion coefficient of the group III nitride semiconductor laser may be greater than the second thermal expansion coefficient of the group III nitride semiconductor laser.

  According to this optical module and nitride semiconductor laser device, it is possible to match the anisotropic thermal expansion coefficient of the group III nitride semiconductor laser with the anisotropic thermal expansion coefficient of the submount.

  In the optical module and the nitride semiconductor laser device according to the present invention, the c-axis of the gallium nitride single crystal base of the submount forms an angle larger than zero with respect to the normal axis to the main surface of the gallium nitride single crystal base. The laser waveguide of the group III nitride semiconductor laser is a reference defined by the c-axis of the gallium nitride single crystal base of the submount and the normal axis of the main surface of the gallium nitride single crystal base of the submount. It preferably extends along a plane.

  According to the optical module and the nitride semiconductor laser device, the laser waveguide of the group III nitride semiconductor laser is defined by the c-axis of the gallium nitride single crystal base and the normal axis with respect to the main surface of the gallium nitride single crystal base Since it extends along the plane, the direction of anisotropy of the thermal expansion coefficient in the group III nitride semiconductor laser can be matched with the direction of the anisotropy of the thermal expansion coefficient in the submount.

  In the optical module and the nitride semiconductor laser device according to the present invention, the substrate is preferably made of the same material as the gallium nitride single crystal base.

  According to this optical module and nitride semiconductor laser device, since the substrate and the gallium nitride single crystal base are made of the same material, the thermal expansion coefficient of the group III nitride semiconductor laser is close to that of the gallium nitride single crystal base material.

  In the optical module and the nitride semiconductor laser device according to the present invention, the submount includes a metal layer provided on the main surface of the gallium nitride single crystal base, and the group III nitride semiconductor laser includes the It is preferable to be fixed to the metal layer of the submount by a conductive adhesive member.

  According to this optical module and nitride semiconductor laser device, the anisotropy of the thermal expansion coefficient in the submount is exhibited through the metal layer of the submount.

  In the optical module according to the present invention, the stem includes a metal base having a side surface on which the nitride semiconductor laser device is mounted, and a metal base having a main surface and a back surface on which the metal base is mounted. Preferably, the metal base includes a through hole extending in a direction from the main surface toward the back surface, and a lead terminal held in the through hole.

  According to this optical module, heat from the group III nitride semiconductor laser of the nitride semiconductor laser device is conducted to the metal base via the metal pedestal.

  In the nitride semiconductor laser device according to the present invention, the group III nitride semiconductor laser includes a first element thermal expansion coefficient in a first in-plane direction along the mounting surface, and a second in-plane direction along the mounting surface. The first in-plane direction is perpendicular to the second in-plane direction, and the first thermal expansion coefficient of the group III nitride semiconductor laser is the gallium nitride based semiconductor. The mounting surface has a first submount thermal expansion coefficient with respect to the first in-plane direction and a second submount thermal expansion coefficient with respect to the second in-plane direction. The first submount coefficient of thermal expansion of the submount is greater than the second submount coefficient of thermal expansion of the submount.

  A submount for mounting a semiconductor laser according to the present invention includes a gallium nitride single crystal base having a semipolar or nonpolar main surface, and has a mounting surface, the mounting surface being along the mounting surface A first thermal expansion coefficient related to the first in-plane direction, and a second thermal expansion coefficient related to the second in-plane direction along the mounting surface, wherein the first in-plane direction is orthogonal to the second in-plane direction. The first thermal expansion coefficient is different from the second thermal expansion coefficient.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

  As described above, according to the present invention, the heat between the group III nitride semiconductor laser and the submount that uses the substrate main surface inclined with respect to the first reference plane orthogonal to the c-axis of the gallium nitride semiconductor. There is provided an optical module capable of reducing variation in characteristics of a group III nitride semiconductor laser related to an expansion coefficient difference and anisotropy of a thermal expansion coefficient. The present invention also provides a nitride semiconductor laser device for an optical module. Furthermore, according to the present invention, a submount for a nitride semiconductor laser device is provided.

FIG. 1 is a drawing schematically showing an optical module according to the present embodiment. FIG. 2 is a drawing schematically showing the optical module and the nitride semiconductor laser device according to the present embodiment. FIG. 3 is a drawing showing main steps in the method of manufacturing the nitride semiconductor laser device according to the present embodiment. FIG. 4 is a drawing showing the structure of a laser diode used in the example. FIG. 5 is a drawing showing the structure of a nitride semiconductor laser device fabricated in the example. FIG. 6 is a drawing showing the relationship between thermal conductivity and thermal resistance when the submount including a gallium nitride single crystal base has a thickness of 100 μm and 300 μm.

  Subsequently, embodiments of the present invention relating to an optical module, a semiconductor laser device, and a submount will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

  FIG. 1 is a drawing schematically showing an optical module according to the present embodiment. FIG. 2 is a drawing schematically showing the optical module and the nitride semiconductor laser device according to the present embodiment. Referring to FIGS. 1 and 2, a nitride semiconductor laser device 1 and an optical module 10 are shown, and a group III nitride semiconductor laser 11 is shown as a semiconductor light emitting element. The optical module 10 includes a nitride semiconductor laser device 1. The optical module 10 includes a stem 10a on which the nitride semiconductor laser device 1 is mounted, and a cap 10b that covers the nitride semiconductor laser device 1 on the stem 10a. The nitride semiconductor laser device 1 includes a submount 3 and a group III nitride semiconductor laser 11. The submount 3 includes a mounting surface 3a and a hexagonal gallium nitride single crystal base 3d having a semipolar or nonpolar main surface. The submount 3 has a mounting surface 3a having anisotropy in thermal expansion coefficient. If necessary, the mounting surface 3a of the submount 3 can be provided with a first electrode 5a and a second electrode 5b on the main surface on the gallium nitride single crystal base 3d. A mounting surface 3 a of the submount 3 mounts a nitride semiconductor light emitting element such as a group III nitride semiconductor laser 11. Part (b) of FIG. 1 is a drawing schematically showing the structure of the group III nitride semiconductor laser device according to the present embodiment. The group III nitride semiconductor laser 11 includes a laser structure 13 and electrodes 15 and 41.

  Although group III nitride semiconductor laser 11 has a gain guide type structure, the present embodiment is not limited to the gain guide type structure, and, for example, a ridge type structure is applied. The group III nitride semiconductor laser 11 includes a laser structure 13 and an electrode 15. The laser structure 13 includes an epitaxial semiconductor stack (hereinafter referred to as “semiconductor stack”) 19 made of a group III nitride semiconductor and a substrate 17 on which the semiconductor stack 19 is mounted. The semiconductor stack 19 is provided on the main surface 17 a of the substrate 17. The electrode 15 is provided on the semiconductor stack 19. The substrate 17 is made of a hexagonal gallium nitride semiconductor and has a main surface 17a and a back surface 17b. The main surface 17a of the substrate 17 is inclined with respect to a first reference plane (for example, the surface Sc) orthogonal to the c-axis of the gallium nitride semiconductor of the substrate 17, and has a polarity characteristic different from the polarity of the c-plane. Have. The semiconductor stack 19 includes an active layer 25. In one embodiment, the active layer 25 is provided so that the oscillation wavelength of the group III nitride semiconductor laser 11 is in the range of 400 nm to 550 nm. The c-axis (axis facing the vector VC) in the semiconductor stack 19 is inclined with respect to the normal axis NX with respect to the main surface 17a of the substrate 17.

  According to this optical module 10, the principal surface 17 a of the substrate 17 of the group III nitride semiconductor laser 11 is inclined with respect to a reference plane orthogonal to the c-axis of the gallium nitride semiconductor of the substrate 17. The substrate 17 of the semiconductor laser 11 has anisotropy with respect to the thermal expansion coefficient. The group III nitride semiconductor laser 11 is provided on the mounting surface 3a of the submount 3 including a hexagonal gallium nitride single crystal base having a semipolar or nonpolar main surface. The main surface of the gallium nitride single crystal base 3d has anisotropy with respect to the thermal expansion coefficient. Therefore, the group III nitride semiconductor laser 11 having an anisotropic thermal expansion coefficient can be mounted on the main surface 3a of the submount 3 including the gallium nitride single crystal base 3d having an anisotropic thermal expansion coefficient. Further, regarding the thermal expansion coefficient as a material, the thermal expansion coefficient of the group III nitride semiconductor laser 11 can be close to the thermal expansion coefficient of the submount 3.

  In this embodiment, the nitride semiconductor laser device 1 is mounted on the stem 10a. The group III nitride semiconductor laser 11 can be mounted on the main surface 3a of the submount 3 in an epi-down configuration.

  The nitride semiconductor laser device 1 can further include a conductive adhesive member 7 for mounting the group III nitride semiconductor laser 11 on the mounting surface 3 a of the submount 3. According to the nitride semiconductor laser device 1, when thermal stress is applied during mounting using the conductive adhesive member 7, it is possible to reduce the occurrence of thermal degradation due to the thermal stress in the electrode.

  According to the optical module 10 and the nitride semiconductor laser device 1, if the group III nitride semiconductor laser 11 is mounted using a submount made of a material different from that of the gallium nitride semiconductor, the submount material and the group III The electrode 15 of the group III nitride semiconductor laser 11 receives heat during mounting due to the difference in thermal expansion coefficient from the material of the nitride semiconductor laser 1. However, in the present embodiment, since the submount 3 includes the gallium nitride single crystal base 3d and has an anisotropic thermal expansion coefficient, the thermal stress during mounting can be reduced. For this reason, the thermal deterioration of the electrode 15 can be reduced.

  The group III nitride semiconductor laser 11 is positioned on the first electrode 5a of the submount 3, and the anode of the nitride semiconductor light emitting element is bonded to the first electrode 5a. The first electrode 5a includes a metal layer. The first electrode 5a may be connected to the lead terminal via a conductive member such as a bonding wire. Further, the cathode of the nitride semiconductor light emitting element 11 may be connected to the second electrode 5b via a conductive member 9 such as a bonding wire, and the second electrode 5b may be connected via a conductive member such as another bonding wire. It may be connected to the lead terminal of the stem. The second electrode 5b includes a metal layer. In one embodiment, a metal layer for the electrodes 5a and 5b can be provided on the main surface of the gallium nitride single crystal base 3d. The group III nitride semiconductor laser 11 is preferably fixed to the electrode 5 a of the submount 3 by the conductive adhesive member 7. According to the nitride semiconductor laser device 1 and the optical module 10, the anisotropy of the thermal expansion coefficient in the submount 3 is exhibited through the electrode 5 a of the submount 3.

  In the optical module 10 and the nitride semiconductor laser device 1, the c-axis of the gallium nitride single crystal base 3d of the submount 3 forms an angle larger than zero with respect to the normal axis of the gallium nitride single crystal base 3d, and the group III nitride The laser waveguide of the semiconductor laser 11 extends along a reference plane defined by the c-axis of the gallium nitride single crystal base 3d of the submount 3 and the normal axis of the main surface of the gallium nitride single crystal base 3d. Is preferred.

  According to the optical module 10 and the nitride semiconductor laser device 1, the laser waveguide of the group III nitride semiconductor laser 11 has a c-axis of the gallium nitride single crystal base 3d and a normal axis with respect to the main surface of the gallium nitride single crystal base 3d. So that the direction of anisotropy of the thermal expansion coefficient in the group III nitride semiconductor laser 11 matches the direction of the anisotropy of the thermal expansion coefficient in the submount 3. Can do.

  In the optical module 10 and the nitride semiconductor laser device 1, the c-axis (vector VC) of the gallium nitride semiconductor of the substrate 17 can be inclined in the direction of the a-axis or m-axis of the group III nitride semiconductor. When the group III nitride semiconductor laser 11 is manufactured using the c-axis substrate 17 inclined in the a-axis or m-axis direction, the group III nitride semiconductor laser 11 has an anisotropic thermal expansion coefficient.

  In the mounting surface 3a of the submount 3 shown in FIG. 2, the first in-plane direction along the mounting surface 3a (one of the X-axis direction and the Y-axis direction in FIG. 2) and the second in-plane along the mounting surface 3a. A direction (the other of the X-axis direction and the Y-axis direction in FIG. 2) is defined. In the nitride semiconductor laser device 1 and the optical module 10, the mounting surface 3a includes the first submount thermal expansion coefficient CM1 (Ex) in the first in-plane direction (for example, the Y-axis direction in FIG. 2) and the second in-plane direction. A second submount thermal expansion coefficient CM2 (Ex) in relation to (for example, the X-axis direction in FIG. 2). The first in-plane direction is orthogonal to the second in-plane direction. The group III nitride semiconductor laser 1 includes a first element thermal expansion coefficient CS1 (Ex) in a first in-plane direction (for example, the Y-axis direction in FIG. 2) and a second in-plane direction (for example, the X-axis direction in FIG. 2). And a second element thermal expansion coefficient CS2 (Ex).

  For example, the first submount thermal expansion coefficient CM1 (Ex) of the submount 3 is larger than the second submount thermal expansion coefficient CM2 (Ex) of the submount, and the first thermal expansion coefficient CS1 of the group III nitride semiconductor laser 11 ( The group III nitride semiconductor laser 11 can be mounted on the submount 3 such that (Ex) is larger than the second thermal expansion coefficient CS2 (Ex) of the group III nitride semiconductor laser 11. Alternatively, the first submount thermal expansion coefficient CM1 (Ex) of the submount 3 is smaller than the second submount thermal expansion coefficient CM2 (Ex) of the submount, and the first thermal expansion coefficient CS1 of the group III nitride semiconductor laser 11 ( The group III nitride semiconductor laser 11 can be mounted on the submount 3 such that (Ex) is smaller than the second thermal expansion coefficient CS2 (Ex) of the group III nitride semiconductor laser 11. According to the optical module 10 and the nitride semiconductor laser device 1 having such a configuration, the anisotropic thermal expansion coefficient in the group III nitride semiconductor laser 11 is matched with the anisotropic thermal expansion coefficient of the submount 3. be able to.

  The substrate 17 of the group III nitride semiconductor laser 11 is preferably made of the same material as the gallium nitride single crystal base 3d. In this embodiment, since the substrate 17 and the gallium nitride single crystal base 3d are made of the same material, the thermal expansion coefficient and the anisotropy of the group III nitride semiconductor laser 11 can be made closer to the material of the gallium nitride single crystal base 3d. .

  In the optical module 10 and the nitride semiconductor laser device 1, the submount main surface 3a is preferably inclined at an angle of 10 degrees or more from the c-plane of the gallium nitride single crystal base 3d. When the submount main surface 3a is inclined from the above-described angle range c-plane, it is preferable to provide the submount 3 with an anisotropic thermal expansion coefficient. In the optical module 10 and the nitride semiconductor laser device 1, the submount main surface 3a is preferably inclined at an angle of 80 degrees or more from the c-plane of the gallium nitride single crystal base 3d. When the submount main surface 3a is inclined from the c-plane at an angle of 80 degrees or more, it is preferable to provide the submount with an anisotropic thermal expansion coefficient of the nonpolar surface of gallium nitride. The submount main surface 3a is preferably inclined at an angle of 90 degrees or less from the c-plane of the gallium nitride single crystal base 3d.

  In the group III nitride semiconductor laser 11 for the nitride semiconductor laser device 1 and the optical module 10, the semiconductor stack 19 includes a p-type gallium nitride based semiconductor layer (for example, “layer 33”) with which the electrode 15 is in contact. In addition, the main surface 17a of the substrate 17 is preferably inclined at an angle of 10 degrees or more with respect to the first reference surface (for example, Sc). According to the optical module 10 and the nitride semiconductor laser device 1, since the semiconductor stack 19 is provided on the main surface 17 a of the substrate 17, the bonding surface 30 a between the electrode 15 and the p-type gallium nitride based semiconductor layer is also the reference surface ( For example, it is inclined at an angle of 10 degrees or more with respect to the surface Sc). Further, the joint surface 30a is also inclined at an angle of 90 degrees or less with respect to a reference surface (for example, the surface Sc).

  When the semipolar surface 17a of the substrate 18 is inclined at an angle ALPHA within a range of 63 degrees or more and 80 degrees or less in the m-axis direction with respect to the c-axis of the hexagonal Group III gallium nitride semiconductor, The interface with the p-type contact layer 33 in contact with the electrode 15 is also inclined at the angle ALPHA described above. At this time, in the nitride semiconductor laser device 1, the angle formed by the c-axis of the gallium nitride semiconductor of the substrate 17 (the direction of the vector VC) and the c-axis of the gallium nitride single crystal base 3d of the submount 3 is within 45 degrees. It is preferable. According to the nitride semiconductor laser device 1, when the angle formed between the c-axis of the gallium nitride semiconductor of the substrate 17 and the c-axis of the gallium nitride single crystal base 3d of the submount 3 is within the above angle, the nitridation of the substrate 17 is performed. The inclination of the c-axis of the gallium semiconductor can be close to the inclination of the c-axis of the gallium nitride single crystal base.

  In the above angle range, the p-side electrode 15 of the group III nitride semiconductor laser 11 is liable to cause deterioration in current-voltage characteristics. In an example of the deterioration of the current-voltage characteristic, the good ohmic characteristic is lost, and the current-voltage characteristic of the electrode 15 is deteriorated so as to exhibit a Schottky characteristic or a characteristic close to the Schottky characteristic. According to the knowledge of the inventor, such electrode characteristic deterioration occurs remarkably in the electrode 15 formed on the semipolar surface of the gallium nitride semiconductor. When the group III nitride semiconductor laser 11 is exposed to stress due to a process temperature of about 200 degrees Celsius after manufacture, for example, the current-voltage characteristics of the electrode 15 are easily deteriorated.

  In addition to such electrode characteristic deterioration (that is, thermal deterioration), in another example of deterioration, a group III nitride semiconductor laser 11 is soldered onto an AlN submount having an isotropic thermal expansion coefficient. In the forward voltage (Vf) of the group III nitride semiconductor laser 11 mounted on the AlN submount, the value after mounting is plus 0.2 volts (50 mA) with respect to the value before mounting. Injection current). However, when the group III nitride semiconductor laser 11 is mounted on a submount including the hexagonal gallium nitride single crystal base 3d having a semipolar or nonpolar main surface and including the mounting surface 3a, The difference from the value before mounting is almost 0 volts. Therefore, not only the thermal deterioration of the electrode but also the characteristic variation of the electrode (that is, thermal variation) also includes a hexagonal gallium nitride single crystal base 3d having a semipolar or nonpolar main surface, and has a mounting surface 3a. The submount 3 can reduce the above-described thermal deterioration and thermal fluctuation.

  The electrode 15 is provided on the semiconductor stack 19 of the laser structure 13. The semiconductor stack 19 includes a first cladding layer 21, a second cladding layer 23, and an active layer 25. The first cladding layer 21 is made of a first conductivity type gallium nitride semiconductor, and is made of, for example, n-type AlGaN, n-type InAlGaN, or the like. The second cladding layer 23 is made of a second conductivity type gallium nitride based semiconductor, for example, p-type AlGaN, p-type InAlGaN, or the like. The active layer 25 is provided between the first cladding layer 21 and the second cladding layer 23. The active layer 25 includes a gallium nitride based semiconductor layer, and this gallium nitride based semiconductor layer is, for example, a well layer 25a. The active layer 25 includes a barrier layer 25b made of a gallium nitride semiconductor, the well layer 25a is provided between the barrier layers 25b, and the layers 25a and 25b are alternately arranged. The well layer 25a is made of, for example, InGaN, and the barrier layer 25b is made of, for example, GaN, InGaN, or the like. The active layer 25 may include a quantum well structure. The first cladding layer 21, the second cladding layer 23, and the active layer 25 are arranged along the normal axis NX of the semipolar main surface 17a. Use of the semipolar main surface 17a is suitable for generation of light having a wavelength of 480 nm or more and 540 nm or less. According to the nitride semiconductor laser device 1 and the optical module 10, the group III nitride semiconductor laser 11 can provide laser oscillation within the above wavelength range indicating light of green and its adjacent color. In the group III nitride semiconductor laser 11, the active layer 25 is preferably provided so as to have an oscillation wavelength in the range of 510 nm or more and 540 nm or less. According to the nitride semiconductor laser device 1 and the optical module 10, the group III nitride semiconductor laser 11 can provide laser oscillation within the above wavelength range indicating green light.

  In the group III nitride semiconductor laser 11 in this example, the c-axis of the hexagonal group III nitride semiconductor is inclined in the direction of the m-axis of the hexagonal group III nitride semiconductor. Therefore, the laser structure 13 includes a first end face 27 and a second end face 29 that intersect the mn plane defined by the m-axis and the normal axis NX of the hexagonal group III nitride semiconductor. Note that the c-axis of the hexagonal group III nitride semiconductor can be inclined in the direction of the a-axis of the hexagonal group III nitride semiconductor. At this inclination, the first end face of the laser structure 13 is formed. 27 and the second end face 29 are formed of a fractured surface that intersects with the a-n plane defined by the a-axis and the normal axis NX of the hexagonal group III nitride semiconductor and is not a cleavage plane. Or the 1st end surface 27 and the 2nd end surface 29 may cross | intersect the surface orthogonal to both the main surface 17a of the board | substrate 17, and an mn surface (or an ann surface).

  Referring to FIG. 2, an orthogonal coordinate system S and a crystal coordinate system CR are depicted. The normal axis NX is directed in the direction of the Z axis of the orthogonal coordinate system S. The main surface 17a extends in parallel to a predetermined plane defined by the X axis and the Y axis of the orthogonal coordinate system S. Further, a representative c-plane Sc is drawn. The c-axis of the hexagonal group III nitride semiconductor of the substrate 17 is inclined at an angle ALPHA greater than zero with respect to the normal axis NX in the m-axis direction of the hexagonal group III nitride semiconductor.

  The group III nitride semiconductor laser 11 further includes an insulating film 31. The insulating film 31 covers the surface 19 a of the semiconductor stack 19 of the laser structure 13, and the semiconductor stack 19 is located between the insulating film 31 and the substrate 17. The substrate 17 is made of a hexagonal group III nitride semiconductor. The insulating film 31 has an opening 31a. The opening 31a extends in the direction of the intersection line LIX between the surface 19a of the semiconductor stack 19 and the mn plane, and has, for example, a stripe shape. The electrode 15 is in contact with the surface 19a (for example, the second conductivity type contact layer 33) of the semiconductor stack 19 through the opening 31a, and extends in the direction of the intersection line LIX. In the group III nitride semiconductor laser 11, the laser waveguide includes the first cladding layer 21, the second cladding layer 23, and the active layer 25, and extends in the direction of the intersection line LIX. On the electrode 15 and the insulating film 31, a pad electrode 16 used for bonding to the submount is provided.

  The main surface 17a of the substrate 17 is made of a hexagonal gallium nitride semiconductor, and the main surface 17 of the substrate 17 has a semipolar surface inclined with respect to the c-axis of the hexagonal gallium nitride semiconductor. The semiconductor stack 19 includes a plurality of semiconductor layers 21, 20, 23, 33 that are epitaxially grown on the main surface 17 a of the substrate 17. According to this nitride semiconductor laser device, a semiconductor stack can be fabricated on the semipolar plane of a hexagonal gallium nitride semiconductor. The main surface 17a of the substrate 17 is preferably made of hexagonal gallium nitride. According to this nitride semiconductor laser device 1, it is possible to produce a semiconductor stack on GaN having good crystal quality.

  In the group III nitride semiconductor laser 11, as already described, when the c-axis is inclined in the direction of the m-axis, the first end face 27 and the second end face 29 are formed with the hexagonal group III nitride semiconductor m. Intersecting the mn plane defined by the axis and the normal axis NX (or when the c-axis is inclined in the direction of the a-axis, the first end face 27 and the second end face 29 are hexagonal group III nitride Intersects the a-n plane defined by the m-axis and the normal axis NX of the physical semiconductor). The laser resonator of the group III nitride semiconductor laser 11 includes first and second end faces 27 and 29, and the laser is directed in the direction of the waveguide axis from one of the first end face 27 and the second end face 29 to the other. The waveguide extends. The laser structure 13 includes a first surface 13a and a second surface 13b, and the first surface 13a is a surface opposite to the second surface 13b. These end faces can be cleaved faces or split sections, depending on the c-axis tilt direction and the laser waveguide extension direction. The first and second end surfaces 27 and 29 extend from the edge 13c of the first surface 13a to the edge 13d of the second surface 13b. In this embodiment, the laser waveguide is along the nm plane. The first and second end faces 27 and 29 are extended, and are different from conventional cleaved faces such as c-plane, m-plane, or a-plane, and have a split section for the optical resonator. The substrate 17 can be made of, for example, GaN. When a substrate made of the gallium nitride semiconductor is used, end faces 27 and 29 that can be used as resonators can be obtained.

  According to the group III nitride semiconductor laser 11, the first and second end faces 27 and 29 constituting the laser resonator intersect with the mn plane. Therefore, it is possible to provide a laser waveguide extending in the direction of the intersecting line between the mn plane and the semipolar plane 17a. Therefore, the group III nitride semiconductor laser 11 has a laser resonator that enables a low threshold current.

  Dielectric multilayer films 43a and 43b provided on at least one of the first and second end faces 27 and 29 or on each of them may be further provided. An end face coat can also be applied to these end faces 27 and 29. With the dielectric multilayer films 43a and 43b, the reflectance can be adjusted by end face coating.

  The group III nitride semiconductor laser 11 includes an n-side light guide layer 35 and a p-side light guide layer 37. The n-side light guide layer 35 includes a first portion 35a and a second portion 35b, and the n-side light guide layer 35 is made of, for example, GaN, InGaN, or the like. The p-side light guide layer 37 includes a first portion 37a and a second portion 37b, and the p-side light guide layer 37 is made of, for example, GaN, InGaN, or the like. The carrier block layer 39 is provided, for example, between the first portion 37a and the second portion 37b.

  Another electrode 41 is provided on the back surface 17b of the substrate 17, and the electrode 41 covers the back surface 17b of the substrate 17, for example. The light guide layers 35 and 37 and the active layer 25 constitute the light emitting layer 20.

  The semiconductor stack 19 includes a light guide layer 35. The light guide layer 35 is in contact with the active layer 25, and the interface 30b between the active layer 25 and the light guide layer 35 is c orthogonal to the c-axis of the gallium nitride semiconductor. The angle ALPHA can be inclined from the surface. When the interface 30b between the active layer 25 and the light guide layer 35 is inclined as described above, the angle ALPHA defines the plane orientation of the active layer 25 in the group III nitride semiconductor laser 11. For example, when the angle ALPHA is in the range of not less than 63 degrees and less than 80 degrees, it is suitable for manufacturing a group III nitride semiconductor laser that generates green light and light of an adjacent wavelength.

  In the group III nitride semiconductor laser 11, the semiconductor stack 19 includes a first conductivity type group III nitride semiconductor region (for example, semiconductor layers 21 and 35a), a light emitting layer 20, and a second conductivity type group III nitride semiconductor region (for example, semiconductor). Layers 37a, 23, 33). The first conductivity type group III nitride semiconductor region (for example, semiconductor layers 21 and 35a), the light emitting layer 20, and the second conductivity type group III nitride semiconductor region (for example, semiconductor layers 37b, 23, and 33) are in the direction of the normal axis NX. They are arranged in order. The electrode 15 is in contact with the main surface of the second conductivity type group III nitride semiconductor region (for example, the semiconductor layers 37a, 23, and 33). The first conductivity type group III nitride semiconductor region (for example, the semiconductor layers 21 and 35a), the light emitting layer 20, and the second conductivity type group III nitride semiconductor region (for example, the semiconductor layers 37b, 23, and 33) each have a normal axis NX. Extends along first to third reference planes R1, R2, and R3 orthogonal to each other.

  The group III nitride semiconductor laser 11 includes a first coefficient of thermal expansion CS1 (Ex) related to a first direction orthogonal to the normal axis NX and a second value related to a second direction orthogonal to the normal axis NX and the first direction. The thermal expansion coefficient CS2 (Ex). The group III nitride semiconductor laser 11 has an anisotropy of thermal expansion coefficient indicating that the first thermal expansion coefficient CS1 (Ex) is larger than the second thermal expansion coefficient CS2 (Ex). This anisotropy is due to the fact that the c-axis is greatly inclined with respect to the normal axis of the main surface 17a of the substrate 17. The group III nitride semiconductor laser 11 is mounted on the main surface 3 a of the submount 3 so as to face the anisotropy of the thermal expansion coefficient of the submount 3. The first direction can be the extending direction of the laser waveguide, for example, and the second direction can be the extending direction of the end faces 27 and 29, for example.

  The submount 3 has a first thermal expansion coefficient CM1 (Ex) related to a third direction orthogonal to the normal line of the main surface 3a, and a second related to a fourth direction orthogonal to the normal line and the third direction. Thermal expansion coefficient CM2 (Ex). The submount 3 has a thermal expansion coefficient anisotropy indicating that the first thermal expansion coefficient CM1 (Ex) is larger than the second thermal expansion coefficient CM2 (Ex). A group III nitride semiconductor laser 11 is mounted on the main surface 3 a of the submount 3 in a direction that matches the anisotropy of the thermal expansion coefficient of the submount 3. For example, the third direction can be defined to coincide with the first direction, and the fourth direction can be defined to coincide with the second direction.

  According to this nitride semiconductor laser device 1, the laser structure 13 includes a semiconductor stack 19 made of a group III nitride semiconductor and a substrate 17 on which the semiconductor stack 19 is mounted. Direction) is inclined with respect to the normal axis NX to the main surface 17a of the substrate 17. Therefore, the semiconductor stack 19 of the group III nitride semiconductor laser 11 is formed on the semipolar surface 17 a instead of the c surface of the substrate 17. The inclination direction of the c-axis of the single crystal gallium nitride base 3d is a direction along a reference plane defined by the vector VC and the normal axis NX.

  The submount 3 has an anisotropic thermal expansion coefficient indicating, for example, that the first thermal expansion coefficient CM1 (Ex) of the mounting member main surface 3a is larger than the second thermal expansion coefficient CM2 (Ex) of the mounting member main surface 3a. Have sex. Further, the group III nitride semiconductor laser 11 has a heat indicating that the first thermal expansion coefficient CS1 (Ex) of the group III nitride semiconductor laser 11 is larger than the second thermal expansion coefficient CS2 (Ex) of the semiconductor light emitting device. Anisotropy of expansion coefficient. The semiconductor laser element is oriented according to the anisotropy of the thermal expansion coefficient of the submount 3 and mounted on the mounting member main surface 3a having the anisotropy of the thermal expansion coefficient. Therefore, when the group III nitride semiconductor laser 11 is mounted on the mounting member main surface 3a having anisotropy of the thermal expansion coefficient, it is mounted on the mounting member main surface 3a having an isotropic thermal expansion coefficient. In contrast, in nitride semiconductor laser device 1, the stress caused by the difference in thermal expansion coefficient between group III nitride semiconductor laser 11 and submount 3 is reduced in group III nitride semiconductor laser 11.

  In the nitride semiconductor laser device 1, for example, the semiconductor stack 19 of the group III nitride semiconductor laser 11 may be provided between the substrate 17 and the submount 3. In this nitride semiconductor laser device 1, a group III nitride semiconductor laser 11 is mounted in a so-called epi down form. The active layer 25 is closer to the main surface 3 a of the submount 3 than the substrate 17.

  The anisotropy of the submount 3 will be described. In the nitride semiconductor laser device 1, the main surface 3a of the submount 3 can be a semipolar or nonpolar surface of gallium nitride, and is formed of a thin metal layer provided on the semipolar or nonpolar surface. Can do. The semipolar or nonpolar surface of the hexagonal single crystal gallium nitride can provide the submount 3 with an anisotropic thermal expansion coefficient. Further, when the main surface 3a of the submount 3 is a semipolar surface, the LD chip can be adapted to both the thermal expansion coefficients (x-axis direction and y-axis direction) having anisotropy. When the main surface 3a of the submount 3 is a non-polar surface, the LD chip has anisotropy that can substantially match both the thermal expansion coefficients (x-axis direction and y-axis direction), and is grown on the c-plane. It is easier to manufacture than a semipolar surface submount in the process of cutting from an ingot. The semipolar or nonpolar surface of single crystal gallium nitride can provide anisotropic thermal expansion to the submount 3.

  The nitride semiconductor laser device 1 is heated via a conductive adhesive member 7 (for example, solder) located between an electrode (for example, the electrode 15) of the group III nitride semiconductor laser 11 and the main surface 3a of the submount 3. Are joined together. The electrode 15 is fixed to the first electrode 5 a of the submount 3 via the conductive adhesive member 7. The expansion and contraction of the group III nitride semiconductor laser 11 is anisotropic due to the heat applied during fixing using the conductive adhesive member 7. When this fixing is performed on the submount 3 (semipolar or nonpolar surface of single crystal gallium nitride), the expansion and contraction of the submount 3 is also anisotropic. Therefore, a very small anisotropic due to the slight difference between the thermal expansion coefficient and its anisotropy of the single crystal gallium nitride submount 3 and the thermal expansion coefficient and its anisotropy of the group III nitride semiconductor laser 11. Residual stress may remain in the nitride semiconductor laser device 1. However, this residual stress can be made sufficiently small.

  In the nitride semiconductor laser device 1, the semipolar main surface 17a is preferably inclined at an angle ALPHA within a range of 10 degrees to 170 degrees with respect to the c-axis of the hexagonal gallium nitride semiconductor. . According to this nitride semiconductor laser device 1, the thermal expansion anisotropy due to the inclination from the c-plane becomes remarkable in the above angle range.

  When the semipolar main surface 17a of the substrate 18 is inclined at an angle ALPHA within a range of 10 degrees to 170 degrees in the m-axis direction with respect to the c-axis of the hexagonal gallium nitride semiconductor, the active layer 25 The peak wavelength of light emission can be in the range of 500 nm to 540 nm. Since the semiconductor stack 19 of the group III nitride semiconductor laser 11 is formed not on the c-plane but on the main surface 17a, the group III nitride semiconductor laser 11 can provide light emission in the above wavelength range (for example, green light emission). .

  FIG. 3 is a drawing showing main steps in the method of manufacturing the nitride semiconductor laser device according to the present embodiment. In the process flow 100 of this manufacturing method, one form of the nitride semiconductor laser device 1 shown in FIGS. 1 and 2 is manufactured.

  In step S101, a mounting member having a main surface exhibiting anisotropy of thermal expansion coefficient is prepared. As the mounting member, for example, the submount 3 shown in FIG. 1 can be used. The submount 3 includes a single crystal gallium nitride base 3d, and the GaN of the single crystal gallium nitride base 3d exhibits, for example, n conductivity. In a later process, a nitride semiconductor light emitting element is mounted on the mounting surface 3 a of the submount 3. More specifically, the mounting surface 3a of the submount 3 includes a first thermal expansion coefficient CM1 (Ex) in the third direction and a second thermal expansion coefficient in the fourth direction orthogonal to the third direction. M2 (Ex). The mounting surface 3a of the submount 3 has an anisotropy of a thermal expansion coefficient, for example, that the first thermal expansion coefficient CM1 (Ex) of the submount 3 is larger than the second thermal expansion coefficient CM1 (Ex) of the submount 3. . The material of the submount 3 is single crystal GaN, and its plane orientation is, for example, a {20-21} plane (a plane in which the c plane is inclined at an angle of 75 degrees in the m plane direction). It corresponds to the GaN substrate of the semiconductor laser mounted on the submount. It is preferable to use a submount having a plane orientation in an angle range of −15 degrees to +45 degrees from the plane orientation of the semiconductor device to be mounted.

  In step S102, a nitride semiconductor light emitting device is prepared. As this nitride semiconductor light emitting device, for example, a group III nitride semiconductor laser 11 can be used. In order to facilitate understanding, in the following description, the structure of the group III nitride semiconductor laser 11 is denoted by the reference numeral shown in FIG. The group III nitride semiconductor laser 11 includes a laser structure 13 and an electrode 15. The group III nitride semiconductor laser 11 in the present embodiment is, for example, a first thermal expansion coefficient CS1 (Ex) in the extending direction of the laser waveguide and a second orthogonal to both the direction of the laser waveguide and the normal direction. And a second coefficient of thermal expansion CS2 (Ex). The semiconductor light emitting element has anisotropy of thermal expansion coefficient. In this anisotropy, as an example, the first thermal expansion coefficient CS1 (Ex) is larger than the second thermal expansion coefficient CS2 (Ex) (or the first 2 is larger than the first thermal expansion coefficient CS1 (Ex)).

  In step S103, the conductive adhesive member 7 can be provided on the submount 3 prior to mounting the semiconductor light emitting element. The conductive adhesive member 7 can be, for example, solder. For example, Au—Sn, Ag—Sn, or the like can be used as the solder. If necessary, the conductive adhesive member 7 can be provided in advance on the electrode of the submount 3. When this submount 3 is used, step S103 is not performed.

  In step S104, the semiconductor light emitting element is oriented in accordance with the anisotropy of the thermal expansion coefficient of the submount 3. For example, the semiconductor light emitting element is oriented with respect to the submount 3 so that the first direction of the semiconductor light emitting element is aligned with the first direction of the submount 3. The submount 3 can have a mark for this orientation (for example, the mark 3c in FIG. 1).

  In step S <b> 105, the semiconductor light emitting element is mounted on the main surface 3 a of the submount 3 after the semiconductor light emitting element is oriented. When the conductive adhesive member 7 is provided on the submount 3, the semiconductor light emitting element is fixed to the submount 3 via the conductive adhesive member 7 in the step of mounting the semiconductor light emitting element. At the time of mounting, the temperature of the submount 3 is raised to a temperature higher than the melting of the solder to melt the solder. After disposing the oriented element on the molten conductive adhesive, the temperature of the submount 3 and the element is lowered to a temperature lower than the melting of the solder to solidify the solder. In this embodiment, as the conductive adhesive member 7, for example, Au—Sn solder (melting point: 300 degrees Celsius) or Sn—Ag solder (melting point: 200 degrees Celsius) is used. The range of the mounting temperature is preferably in the range of 205 degrees Celsius to 340 degrees Celsius, for example. In this manufacturing method, although the thermal stress at the time of fixing using the conductive adhesive member 7 may increase the anisotropic residual stress of the nitride semiconductor laser device 1, the anisotropic thermal expansion coefficient is increased. By using the submount 3 having, the influence of residual stress can be reduced.

  According to this manufacturing method, the laser structure 13 includes the semiconductor stack 19 made of a group III nitride semiconductor and the substrate 17 on which the semiconductor stack 19 is mounted. The c-axis in the semiconductor stack 19 is relative to the main surface 17 a of the substrate 17. It is inclined with respect to the normal axis NX. Therefore, the semiconductor multilayer 19 is formed on the main surface 17a that is not the c-plane. The group III nitride semiconductor laser 11 has anisotropy in thermal expansion coefficient indicating that the first thermal expansion coefficient CS1 (Ex) of the group III nitride semiconductor laser 11 is different from the second thermal expansion coefficient CS2 (Ex). Have This group III nitride semiconductor laser 11 is oriented according to the anisotropy of the thermal expansion coefficient of the submount 3 and mounted on the mounting surface 3a of the submount 3 having the anisotropy of the thermal expansion coefficient. . Therefore, when the group III nitride semiconductor laser 11 is mounted on the mounting surface 3a having anisotropy of the thermal expansion coefficient, the group III nitride semiconductor laser is mounted on the mounting surface 3a having an isotropic thermal expansion coefficient. In the nitride semiconductor laser device 1, the stress due to the thermal expansion coefficient is reduced in the group III nitride semiconductor laser 11 as compared with the device on which the 11 is mounted.

  FIG. 4 is a drawing showing a semiconductor laser module, which is manufactured through the process flow shown in FIG. Referring to FIG. 4A, a semiconductor laser module 71a is shown. The stem 73a includes a metal base including a through hole extending in the first direction and lead terminals 77a, 77b, and 77c held in the through hole, and a metal base 75 having a side surface provided on the metal base. Including. The semiconductor laser device 61a is mounted on the side surface of a metal pedestal (heat sink) 75 on the metal base of the stem 73a. The group III nitride semiconductor laser 12 is firmly fixed to the submount 3 via a conductive adhesive. The group III nitride semiconductor laser 12 can have the same structure as the group III nitride semiconductor laser 11 except that it has a ridge structure. A lens cap 73 b that holds the lens 74 is provided on the stem 73 a, and the stem 73 a and the lens cap 73 b constitute a package 73. The metal stem 73a is made of, for example, iron, and the metal portion of the lens cap 73b is also made of iron. The metal base (heat sink) 75 is made of, for example, copper having excellent thermal conductivity. The stem 73a supports lead terminals 77a, 77b, and 77c. Lead terminal 77 a is connected to heat sink 9 through bonding wire 79 a, and is connected to the anode electrode of group III nitride semiconductor laser 11 through the electrode layer of heat sink 9. The lead terminal 77b is connected to the electrode layer on the mounting surface 3a of the submount 3 via a bonding wire 79b. The lead terminal 77 c is connected to the stem 73. The heat sink 9 is firmly bonded to the anode electrode of the group III nitride semiconductor laser 12 via the conductive adhesive 7. According to this optical module 71a, heat from the group III nitride semiconductor laser 12 of the nitride semiconductor laser device 1 is conducted to the metal base via the metal pedestal 75.

Example 1
An embodiment of a nitride semiconductor laser device will be described. A group III nitride semiconductor laser device is prepared. In this example, a group III nitride semiconductor laser device is prepared by forming the following steps.

(Production of Group III Nitride Semiconductor Laser Device)
The laser diode structure shown in FIG. 5 is produced. A GaN wafer 90 with the c-axis turned off 75 degrees in the m-axis direction was prepared. The plane orientation of the main surface of the GaN wafer 90 is the {20-21} plane. After the GaN wafer 90 is placed in the growth furnace, heat treatment is performed in an atmosphere of ammonia and hydrogen. The heat treatment temperature is 1100 degrees Celsius, and the heat treatment time is about 10 minutes. After the heat treatment, TMG (98.7 μmol / min), TMA (8.2 μmol / min), NH ₃ (6 slm), SiH ₄ are supplied to the growth furnace, and the n-type AlGaN layer 91 for the cladding layer is formed as GaN. It grows on the wafer 90 at 1150 degrees Celsius. The thickness of the n-type AlGaN layer 91 is 2300 nm. The growth rate of the n-type AlGaN layer 91 is 46.0 nm / min. The Al composition of the n-type AlGaN layer 91 is 0.04.

Next, TMG (98.7 μmol / min), NH ₃ (5 slm), and SiH ₄ are supplied to the growth reactor to grow the n-type GaN layer 92 on the n-type AlGaN layer 91 at 1150 degrees Celsius. The n-type GaN layer 92 has a thickness of 50 nm. The growth rate of the n-type GaN layer 92 is 58.0 nm / min. TMG (24.4 μmol / min), TMI (4.6 μmol / min), NH ₃ (6 slm) was supplied to the growth reactor, and an undoped InGaN layer 93a for the light guide layer was formed on the n-type GaN layer 94 in Celsius. Grows at 840 degrees. The n-type InGaN layer 93a has a thickness of 65 nm. The growth rate of the n-type InGaN layer 93a is 6.7 nm / min. The In composition of the undoped InGaN layer 93a is 0.05. Next, an active layer 94 is formed. TMG (15.6 μmol / min), TMI (29.0 μmol / min), and NH ₃ (8 slm) are supplied to the growth reactor to grow an undoped InGaN well layer at 745 degrees Celsius. The thickness of the InGaN layer is 3 nm. The growth rate of the InGaN layer is 3.1 nm / min.

Next, while maintaining the temperature of the growth furnace at 745 degrees Celsius, TMG (15.6 μmol / min), TMI (0.3 μmol / min), NH ₃ (8 slm) was supplied to the growth furnace, and the undoped GaN layer was formed. Grows on the InGaN layer at 745 degrees Celsius. The thickness of the GaN layer is 1 nm. The growth rate of the GaN layer is 3.1 nm / min. After growing the undoped GaN layer, the temperature of the growth furnace is changed from 745 degrees Celsius to 870 degrees Celsius. TMG (24.4 μmol / min), TMI (1.6 μmol / min), NH ₃ (6 slm) was supplied to the growth reactor, and an undoped InGaN layer for the barrier layer was formed on the undoped InGaN well layer at 870 degrees Celsius. grow up. The thickness of the InGaN layer is 15 nm. The growth rate of the InGaN layer is 6.7 nm / min. The In composition of the undoped InGaN layer is 0.02.

Next, the temperature of the growth furnace is changed from 870 degrees Celsius to 745 degrees Celsius. Thereafter, TMG (15.6 μmol / min), TMI (29.0 μmol / min), and NH ₃ (8 slm) are supplied to the growth reactor to grow an undoped InGaN well layer on the InGaN layer at 745 degrees Celsius. The thickness of the InGaN layer is 3 nm. The growth rate of the InGaN layer is 3.1 nm / min. The In composition of the undoped InGaN layer is 0.25.

The growth of the well layer and the barrier layer is repeated twice. Thereafter, TMG (13.0 μmol / min), TMI (4.6 μmol / min), and NH ₃ (6 slm) are supplied to the growth reactor, and an undoped InGaN layer 93 b for the light guide layer is formed on the active layer 94. Grows at 840 degrees Celsius. The thickness of the InGaN layer 93b is 65 nm. The growth rate of the InGaN layer 93b is 6.7 nm / min. Next, TMG (98.7 μmol / min) and NH ₃ (5 slm) are supplied to the growth furnace, and the undoped GaN layer 96 is grown on the InGaN layer 93b at 1100 degrees Celsius. The thickness of the GaN layer 96 is 50 nm. The growth rate of the GaN layer 96 is 58.0 nm / min. The In composition of the undoped InGaN layer 93b is 0.05.

Next, TMG (16.6 μmol / min), TMA (2.8 μmol / min), NH ₃ (6 slm), and Cp ₂ Mg are supplied to the growth reactor, and the p-type AlGaN layer 97 is placed on the GaN layer 96 at 1100 Celsius degrees. Grows at a degree. The thickness of the AlGaN layer 97 is 20 nm. The growth rate of the AlGaN layer 97 is 4.9 nm / min. The Al composition of the p-type AlGaN layer 97 is 0.15. TMG (36.6 μmol / min), TMA (3.0 μmol / min), NH ₃ (6 slm), and Cp ₂ Mg are supplied to the growth reactor, and the p-type AlGaN layer 98 is placed on the p-type AlGaN layer 97 at 1100 Celsius degrees. Grows at a degree. The thickness of the AlGaN layer 98 is 400 nm. The composition of Al is 0.06. The growth rate of the AlGaN layer 98 is 13.0 nm / min. Further, TMG (34.1 μmol / min), NH ₃ (5 slm), and Cp ₂ Mg are supplied to the growth reactor, and the p-type GaN layer 99 is grown on the p-type AlGaN layer 98 at 1100 degrees Celsius. The thickness of the GaN layer 99 is 50 nm. The growth rate of the p-type GaN layer 99 is 18.0 nm / min. An epitaxial wafer is manufactured by these steps.

  After the anode AN and cathode CT are formed on the epitaxial wafer to produce a substrate product, the substrate product can be separated to produce individual laser diodes. The anode electrode is electrically connected to the p-type GaN layer via an insulating film having a stripe window having a width of 10 micrometers, for example. This substrate product is cut in the a plane and a plane perpendicular to the a plane to produce a laser diode LD0 having a length of 600 micrometers and a width of 2 micrometers with the a face as an end face for the pair of resonators.

  The thermal expansion coefficient of the laser diode LD0 is measured. The laser diode LD0 is manufactured using a GaN wafer in which the c-axis of GaN is inclined at an angle of 75 degrees (also referred to as an off angle) in the direction of the m-axis of GaN.

The thermal expansion coefficient CS1 (Ex) in the extending direction (for example, a-axis direction) of the laser waveguide of the laser diode LD0 is 5.6 × 10 ⁻⁶ / K, and the thermal expansion coefficient in the extending direction of the end face of the laser resonator. CS2 (Ex) is 4.6 × 10 ⁻⁶ / K. The extending direction of the laser waveguide of the laser diode is orthogonal to the extending direction of the laser resonator end face (for example, the direction of the mn plane).

The characteristics of GaN single crystal and AlN polycrystal for submount are compared. In the GaN single crystal, the thermal expansion coefficient in the direction orthogonal to the c-axis is 5.59 × 10 ⁻⁶ / K, and the thermal expansion coefficient in the direction parallel to the c-axis is 3.17 × 10 ⁻⁶ / K. The thermal conductivity is 130 W / (m · K). On the other hand, the thermal conductivity of the AlN submount is 170 to 250 W / (m · K), and the thermal expansion coefficient of the AlN submount is 4.7 × 10 ⁻⁶ / K.

(Measurement of thermal resistance and estimation of MTTF)
FIG. 6 shows the relationship between thermal conductivity and thermal resistance at submount thicknesses of 100 μm and 300 μm including a gallium nitride single crystal base. According to the inventor's experiment, the thermal resistance of the nitride semiconductor laser device in the p-down mounting using the AlN submount is 22 ° C./W, while the nitriding in the p-down mounting using the single crystal GaN submount. The thermal resistance of the semiconductor laser device is 26 ° C./W. This result shows that, at an input power of 1 watt (W), the difference in submount results in a junction temperature difference of 4 Kelvin (K). The inventor has estimated the relationship between the thermal expansion coefficient difference and the mean failure life (MTTF) in the nitride semiconductor laser device, and according to this estimate, the increase in the junction temperature of 4 Kelvin (K) Lifespan becomes 1% worse.

  Two substantially equivalent nitride semiconductor lasers (LD chips) prepared on a GaN substrate having a {20-21} plane orientation are prepared. One of them is p-down mounted on a submount including a single crystal gallium nitride base having the same plane orientation as the plane orientation of the GaN substrate of the nitride semiconductor laser (LD chip) to produce a nitride semiconductor laser device GN, The other nitride semiconductor laser is p-down mounted on an available AlN submount to produce a nitride semiconductor laser device (hereinafter referred to as “AN”). In a nitride semiconductor laser device (hereinafter referred to as “GN”), there is substantially no difference in thermal expansion coefficient between the LD chip and the single crystal GaN submount. In the nitride semiconductor laser device AN, a difference in thermal expansion coefficient remains between the LD chip and the AlN submount. Comparing the MTTFs of the results of the LD lifetime test of the nitride semiconductor laser device GN and the nitride semiconductor laser device AN, the lifetime of the nitride semiconductor laser device AN is about 10% shorter than that of the nitride semiconductor laser device GN. Therefore, in the above-described mounting form, a single crystal having a thermal expansion coefficient that is close to the thermal expansion coefficient of the nitride semiconductor laser and matched with the anisotropy of the thermal expansion coefficient even when the junction temperature increases by several degrees. Using a gallium nitride case submount is superior in terms of LD life.

  In the following description, the reference numerals of FIGS. 1 and 2 are used for easy understanding. The first thermal expansion coefficient CM1 (Ex) of the mounting surface of the single crystal gallium nitride submount 3 has anisotropy of the thermal expansion coefficient indicating that the second thermal expansion coefficient CM2 (Ex) of the mounting surface 3a is larger. . Further, the group III nitride semiconductor laser 11 has a heat indicating that the first thermal expansion coefficient CS1 (Ex) of the group III nitride semiconductor laser 11 is larger than the second thermal expansion coefficient CS2 (Ex) of the semiconductor light emitting device. Anisotropy of expansion coefficient. The semiconductor laser element is oriented according to the anisotropy of the thermal expansion coefficient of the submount 3 and mounted on the mounting member main surface 3a having the anisotropy of the thermal expansion coefficient. The group III nitride semiconductor laser 11 is mounted on the mounting surface 3a of the single crystal GaN submount 3 having anisotropy of thermal expansion coefficient, and is mounted on the mounting surface 3a having an isotropic thermal expansion coefficient. In contrast, in the nitride semiconductor laser device 1, the stress caused by the difference in thermal expansion coefficient between the group III nitride semiconductor laser 11 and the submount 3 is reduced in the group III nitride semiconductor laser 11. From the results of other experiments including the above-described experiment, the inclination angle of the GaN substrate of the nitride semiconductor laser (the main surface 17a of the substrate 17 in FIG. 1) is preferably in the angle range of 60 degrees to 90 degrees. The angle difference between the c-axis of the GaN substrate of the semiconductor laser and the c-axis of the single crystal gallium nitride base is preferably in the angle range of −15 degrees to +45 degrees.

  The present invention is not limited to the specific configuration disclosed in the present embodiment.

  As described above, according to the embodiment of the present invention, in the group III nitride semiconductor laser using the substrate main surface inclined with respect to the first reference plane orthogonal to the c-axis of the gallium nitride semiconductor, the submount There is provided an optical module capable of reducing the characteristic variation related to the difference in thermal expansion coefficient and the anisotropy of the thermal expansion coefficient between the semiconductor laser and the group III nitride semiconductor laser. In addition, according to the embodiment of the present invention, a semiconductor laser device for an optical module is provided. Furthermore, according to an embodiment of the present invention, a submount for a semiconductor laser device is provided.

DESCRIPTION OF SYMBOLS 1 ... Nitride semiconductor laser device, 3 ... Single-crystal GaN submount, 3a ... Mounting member main surface, 5a ... 1st electrode, 5b ... 2nd electrode, 7 ... Conductive adhesive member, 9 ... Conductive member, 11 ... Group III nitride semiconductor laser element, 13 ... Laser structure, 13a ... First surface, 13b ... Second surface, 13c, 13d ... Edge, 15 ... Electrode, 17 ... Substrate, 17a ... Main surface, 17b ... Back surface, 19 ... Semiconductor laminated layer, 19a ... Semiconductor region surface, 21 ... First cladding layer, 23 ... Second cladding layer, 25 ... Active layer, 25a ... Well layer, 25b ... Barrier layer, 27, 29 ... Split section , ALPHA ... angle, Sc ... c-plane, NX ... normal axis, 31 ... insulating film, 31a ... insulating film opening, 35 ... n-side light guide layer, 37 ... p-side light guide layer, 39 ... carrier block layer, 41 ... Electrode, 43a, 43b ... Dielectric multilayer film, 71a 71b ... semiconductor laser module, 73a ... stem, 73b ... lens cap, 75 ... heat sink, 77A～77c ... lead terminals, 79a, 79b ... bonding wire.

Claims (19)

A submount including a hexagonal gallium nitride single crystal base having a semipolar or nonpolar main surface and having a mounting surface, and a group III nitride provided on the mounting surface of the submount A nitride semiconductor laser device including a semiconductor laser;
A stem on which the nitride semiconductor laser device is mounted;
With
The group III nitride semiconductor laser includes a substrate having a main surface made of a hexagonal gallium nitride semiconductor, an epitaxial semiconductor stack including an active layer provided on the main surface of the substrate, and the epitaxial semiconductor stack Including an electrode provided on the
The main surface of the substrate is inclined with respect to a first reference plane orthogonal to the c-axis of the gallium nitride based semiconductor,
The mounting surface of the submount exhibits anisotropy of thermal expansion coefficient;
An angle formed by the c-axis of the gallium nitride based semiconductor of the substrate and the c-axis of the gallium nitride single crystal base of the submount is within 45 degrees;
An optical module in which the oscillation wavelength of the group III nitride semiconductor laser is in a range of 400 nm to 550 nm. The epitaxial semiconductor stack includes a p-type gallium nitride based semiconductor layer in contact with the electrode,
The optical module according to claim 1, wherein the main surface of the substrate is inclined at an angle of 10 degrees or more with respect to the first reference surface. The optical module according to claim 1, wherein the group III nitride semiconductor laser is mounted on the mounting surface of the submount in an epi-down form. 4. The optical module according to claim 1 , further comprising a conductive adhesive member that mounts the group III nitride semiconductor laser on the mounting surface of the submount. 5. 5. The optical module according to claim 1 , wherein an oscillation wavelength of the group III nitride semiconductor laser is in a range from 480 nm to 540 nm. The optical module according to any one of claims 1 to 5 , wherein an oscillation wavelength of the group III nitride semiconductor laser is in a range of 510 nm or more and 540 nm or less. The c-axis of the gallium nitride-based semiconductor of the substrate forms an inclined either in one direction of the a-axis and m-axis of the gallium nitride based semiconductor, according to any one of claims 1 to 6 Optical module. The epitaxial semiconductor stack includes a light guide layer;
The light guide layer is in contact with the active layer;
8. The interface according to claim 1 , wherein an interface between the active layer and the light guide layer forms an inclination of an angle ALPHA from a reference plane orthogonal to the c-axis of the gallium nitride semiconductor. Optical module. The optical module according to claim 8 , wherein the angle ALPHA is in a range of 63 degrees or more and less than 80 degrees. The optical module according to any one of claims 1 to 9 , wherein the mounting surface is inclined at an angle of 10 degrees or more from a c-plane of the gallium nitride single crystal base. The optical module according to any one of claims 1 to 10 , wherein the mounting surface is inclined at an angle of 80 degrees or more from a c-plane of the gallium nitride single crystal base. The mounting surface has a first submount thermal expansion coefficient related to a first in-plane direction along the mounting surface and a second submount thermal expansion coefficient related to a second in-plane direction along the mounting surface;
The first in-plane direction is orthogonal to the second in-plane direction,
The first submount thermal expansion coefficient of the submount is greater than the second submount thermal expansion coefficient of the submount;
The group III nitride semiconductor laser has a first element thermal expansion coefficient related to the first in-plane direction and a second element thermal expansion coefficient related to the second in-plane direction,
The III said first element thermal expansion coefficient of the nitride semiconductor laser is greater than the second element thermal expansion coefficient of the III nitride semiconductor laser, as claimed in any one of claims 1 to 11 Optical module. The c-axis of the gallium nitride single crystal base of the submount forms an angle greater than zero with respect to the normal axis of the main surface of the gallium nitride single crystal base;
The group III nitride semiconductor laser has a laser waveguide in a reference plane defined by the c-axis of the gallium nitride single crystal base of the submount and the normal axis of the main surface of the gallium nitride single crystal base. The optical module according to claim 1 , which extends along the optical module. 14. The optical module according to claim 1 , wherein the substrate is made of the same material as the gallium nitride single crystal base. The stem includes a metal base having a side surface on which the nitride semiconductor laser device is mounted, and a metal base having a main surface and a back surface on which the metal base is mounted,
The stem includes a through hole extending in a direction toward the back side from the main surface of the metal base, and a lead terminals held in the through-hole, any one of claims 1 to 14 The optical module described in 1. The submount includes a metal layer provided on the main surface of the gallium nitride single crystal base,
The optical module according to any one of claims 1 to 15 , wherein the group III nitride semiconductor laser is fixed to the metal layer of the submount by a conductive adhesive member. A nitride semiconductor laser device,
A submount including a mounting surface including a gallium nitride single crystal base having a semipolar or nonpolar main surface;
A group III nitride semiconductor laser provided on the mounting surface of the submount;
With
The group III nitride semiconductor laser includes a substrate having a main surface made of a group III gallium nitride based semiconductor, and an epitaxial semiconductor stack including an active layer provided on the main surface of the substrate,
The main surface of the substrate is inclined with respect to a reference plane orthogonal to the c-axis of the gallium nitride based semiconductor,
The mounting surface of the submount exhibits anisotropy of thermal expansion coefficient;
An angle formed by the c-axis of the gallium nitride based semiconductor of the substrate and the c-axis of the gallium nitride single crystal base of the submount is within 45 degrees;
An oscillation wavelength of the group III nitride semiconductor laser is a nitride semiconductor laser device in a range of 400 nm to 550 nm. The group III nitride semiconductor laser has a first element thermal expansion coefficient related to a first in-plane direction along the mounting surface and a second element thermal expansion coefficient related to a second in-plane direction along the mounting surface. And
The first in-plane direction is orthogonal to the second in-plane direction,
The first element thermal expansion coefficient of the group III nitride semiconductor laser is larger than the second element thermal expansion coefficient of the group III nitride semiconductor laser;
The mounting surface has a first submount thermal expansion coefficient related to the first in-plane direction and a second submount thermal expansion coefficient related to the second in-plane direction,
18. The nitride semiconductor laser device according to claim 17 , wherein the first submount thermal expansion coefficient of the submount is larger than the second submount thermal expansion coefficient of the submount. A substrate having a main surface made of a hexagonal gallium nitride semiconductor, an epitaxial semiconductor stack including an active layer provided on the main surface of the substrate, and an electrode provided on the epitaxial semiconductor stack A submount for mounting a group III nitride semiconductor laser including :
The main surface of the substrate of the group III nitride semiconductor laser is inclined with respect to a first reference plane orthogonal to the c-axis of the gallium nitride semiconductor,
The oscillation wavelength of the group III nitride semiconductor laser is in the range of 400 nm to 550 nm,
The submount includes a gallium nitride single crystal base having a semipolar or nonpolar main surface, and has a mounting surface;
The mounting surface has a first thermal expansion coefficient related to a first in-plane direction along the mounting surface and a second thermal expansion coefficient related to a second in-plane direction along the mounting surface;
The first in-plane direction is orthogonal to the second in-plane direction,
It said first coefficient of thermal expansion I different from the second thermal expansion coefficient, the mounting surface of the submount indicates the anisotropy of thermal expansion coefficient,
A submount in which an angle formed between the c axis of the gallium nitride based semiconductor of the substrate and the c axis of the gallium nitride single crystal base of the submount is within 45 degrees .

Images