Group-iii nitride semiconductor laser device, and method for fabricating group-iii nitride semiconductor laser device

Abstract

Provided is a group-III nitride semiconductor laser device with a laser cavity of high lasing yield, on a semipolar surface of a support base in which the c-axis of a hexagonal group-III nitride is tilted toward the m-axis. First and second fractured faces 27, 29 to form the laser cavity intersect with an m-n plane. The group-III nitride semiconductor laser device 11 has a laser waveguide extending in a direction of an intersecting line between the m-n plane and the semipolar surface 17 a. For this reason, it is feasible to make use of emission by a band transition enabling the low threshold current. In a laser structure 13, a first surface 13 a is opposite to a second surface 13 b. The first and second fractured faces 27, 29 extend from an edge 13 c of the first surface 13 a to an edge 13 d of the second surface 13 b. The fractured faces are not formed by dry etching and are different from conventionally-employed cleaved facets such as c-planes, m-planes, or a-planes.

1 . A group-III nitride semiconductor laser device comprising:
 a laser structure including a support base and a semiconductor region, the support base comprising a hexagonal group-III nitride semiconductor and having a semipolar principal surface, the semiconductor region being provided on the semipolar principal surface of the support base; and   an electrode being provided on the semiconductor region of the laser structure,   the semiconductor region including a first cladding layer of a first conductivity type gallium nitride-based semiconductor, a second cladding layer of a second conductivity type gallium nitride-based semiconductor, and an active layer, the active layer being provided between the first cladding layer and the second cladding layer,   the first cladding layer, the second cladding layer, and the active layer being arranged along a normal axis to the semipolar principal surface,   the active layer including a gallium nitride-based semiconductor layer,   a c-axis of the hexagonal group-III nitride semiconductor of the support base tilting at a finite angle ALPHA with respect to the normal axis toward an m-axis of the hexagonal group-III nitride semiconductor,   the angle ALPHA falling within a range of not less than 45° and not more than 80° or within a range of not less than 100° and not more than 135°,   the laser structure including first and second fractured faces, the first and second fractured faces intersecting with an m-n plane defined by the m-axis of the hexagonal group-III nitride semiconductor and the normal axis,   a laser cavity of the group-III nitride semiconductor laser device including the first and second fractured faces,   the laser structure including first and second surfaces, the first surface is opposite to the second surface,   each of the first and second fractured faces extending from an edge of the first surface to an edge of the second surface,   an end face of the support base and an end face of the semiconductor region being exposed in each of the first and second fractured faces, and   the first and second fractured faces including a region such that an angle between this region and a plane indicated by plane index (−1, 0, 1, L) or (1, 0, −1, −L) falls within a range of not less than −5° and not more than +5°, with L as an integer number not less than 4.   
     
     
         2 . The group-III nitride semiconductor laser device according to  claim 1 , wherein the first and second fractured faces can include a region such that an angle formed by this region and the arrangements of N atom —Ga atom extending toward a direction tilting at an angle of 70.53° in the direction opposite to the direction of the m-axis of the hexagonal group-III nitride semiconductor with respect to the direction of the c-axis of the hexagonal group-III nitride semiconductor, falls within a range of not less than −10° and not more than +10°. 
     
     
         3 . The group-III nitride semiconductor laser device according to  claim 1 , wherein a part of the first and second fractured faces that is included in the active layer can include a part of or the whole of an region such that an angle between this region and the plane indicated by plane index (−1, 0, 1, L) or (1, 0, −1, −L) falls within a range of not less than −5° and not more than +5°. 
     
     
         4 . The group-III nitride semiconductor laser device according to  claim 1 , wherein a part of the first and second fractured faces that is included in the active layer can include a part of or the whole of an region such that an angle formed by this region and the arrangements of N atom —Ga atom extending toward a direction tilting at an angle of 70.53° in the direction opposite to the direction of the m-axis of the hexagonal group-III nitride semiconductor with respect to the direction of the c-axis of the hexagonal group-III nitride semiconductor, falls within a range of not less than −10° and not more than +10°. 
     
     
         5 . The group-III nitride semiconductor laser device according to  claim 1 , wherein the angle ALPHA falls within a range of not less than 63° and not more than 80° or within a range of not less than 100° and not more than 117°. 
     
     
         6 . The group-III nitride semiconductor laser device according to  claim 1 , wherein a thickness of the support base is not more than 400 μm. 
     
     
         7 . The group-III nitride semiconductor laser device according to  claim 1 , wherein a thickness of the support base is not less than 50 μm and not more than 100 μm. 
     
     
         8 . The group-III nitride semiconductor laser device according to  claim 1 , wherein laser light from the active layer is polarized in a direction of an a-axis of the hexagonal group-III nitride semiconductor. 
     
     
         9 . The group-III nitride semiconductor laser device according to  claim 1 , wherein light in an LED mode of the group-III nitride semiconductor laser device includes a polarization component I 2  in a direction indicated by a projection of the c-axis of the hexagonal group-III nitride semiconductor onto the principal surface, and a polarization component I 1  in the direction of an a-axis of the hexagonal group-III nitride semiconductor, and
 wherein the polarization component I 1  is greater than the polarization component I 2 . 
 
     
     
         10 . The group-III nitride semiconductor laser device according to  claim 1 , wherein the semipolar principal surface is slightly tilted in a range of not less than −4° and not more than +4° with respect to any one of {20-21} plane, {10-11} plane, {20-2-1} plane, and {10-1-1} plane. 
     
     
         11 . The group-III nitride semiconductor laser device according to  claim 1 , wherein the semipolar principal surface is any one of {20-21} plane, {10-11} plane, {20-2-1} plane, and {10-1-1} plane. 
     
     
         12 . The group-III nitride semiconductor laser device according to  claim 1 , wherein a stacking fault density of the support base is not more than 1×10 4  cm −1 . 
     
     
         13 . The group-III nitride semiconductor laser device according to  claim 1 , wherein the support base comprises any one of GaN, AlGaN, AlN, InGaN, and InAlGaN. 
     
     
         14 . The group-III nitride semiconductor laser device according to  claim 1 , further comprising a dielectric multilayer film provided on at least one of the first and second fractured faces. 
     
     
         15 . The group-III nitride semiconductor laser device according to  claim 1 , wherein the active layer includes a light emitting region provided so as to generate light at a wavelength of not less than 360 nm and not more than 600 nm. 
     
     
         16 . The group-III nitride semiconductor laser device according to  claim 1 , wherein the active layer includes a quantum well structure provided so as to generate light at a wavelength of not less than 430 nm and not more than 550 nm. 
     
     
         17 . A method for fabricating a group-III nitride semiconductor laser device, the method comprising the steps of:
 preparing a substrate of a hexagonal group-III nitride semiconductor, the substrate having a semipolar principal surface;   forming a substrate product that has a laser structure, an anode electrode and a cathode electrode, the laser structure including the substrate and a semiconductor region, the semiconductor region being formed on the semipolar principal surface;   scribing a first surface of the substrate product in part in a direction of an a-axis of the hexagonal group-III nitride semiconductor; and   carrying out breakup of the substrate product by press against a second surface of the substrate product, to form another substrate product and a laser bar,   the first surface being opposite to the second surface,   the semiconductor region being located between the first surface and the substrate,   the laser bar having first and second end faces, the first and second end faces being formed by the breakup, and the first and second end faces extending from the first surface to the second surface,   the first and second end faces constituting a laser cavity of the group-III nitride semiconductor laser device,   the anode electrode and the cathode electrode being formed on the laser structure,   the semiconductor region comprising a first cladding layer of a first conductivity type gallium nitride-based semiconductor, a second cladding layer of a second conductivity type gallium nitride-based semiconductor and an active layer, the active layer being provided between the first cladding layer and the second cladding layer,   the first cladding layer, the second cladding layer, and the active layer being arranged along a normal axis to the semipolar principal surface,   the active layer comprising a gallium nitride-based semiconductor layer,   a c-axis of the hexagonal group-III nitride semiconductor of the substrate tilting at an angle ALPHA with respect to the normal axis toward an m-axis of the hexagonal group-III nitride semiconductor,   the angle ALPHA falling within a range of not less than 45° and not more than 80° or within a range of not less than 100° and not more than 135°,   the first and second end faces intersecting with an m-n plane defined by the m-axis of the hexagonal group-III nitride semiconductor and the normal axis, and   the first and second end faces including a region such that an angle between this region and a plane indicated by plane index (−1, 0, 1, L) or (1, 0, −1, −L) falls within a range of not less than −5° and not more than +5°, with L as an integer number not less than 4.   
     
     
         18 . The method according to  claim 17 , wherein the first and second end faces can include a region such that an angle formed by this region and the arrangements of N atom —Ga atom extending toward a direction tilting at an angle of 70.53° in the direction opposite to the direction of the m-axis of the hexagonal group-III nitride semiconductor with respect to the direction of the c-axis of the hexagonal group-III nitride semiconductor, falls within a range of not less than −10° and not more than +10°. 
     
     
         19 . The method according to  claim 17 , wherein a part of the first and second end faces that is included in the active layer can include a part of or the whole of a region such that an angle between this region and the plane indicated by plane index (−1, 0, 1, L) or (1, 0, −1, −L) falls within a range of not less than −5° and not more than +5°. 
     
     
         20 . The method according to  claim 17 , wherein a part of the first and second end faces that is included in the active layer can include a part of or the whole of a region such that an angle formed by this region and the arrangements of N atom —Ga atom extending toward a direction tilting at an angle of 70.53° in the direction opposite to the direction of the m-axis of the hexagonal group-III nitride semiconductor with respect to the direction of the c-axis of the hexagonal group-III nitride semiconductor, falls within a range of not less than −10° and not more than +10°. 
     
     
         21 . The method according to  claim 17 , wherein the angle ALPHA falls within a range of not less than 63° and not more than 80° or within a range of not less than 100° and not more than 117°. 
     
     
         22 . The method according to  claim 17 , wherein the step of forming the substrate product comprises performing processing such as slicing or grinding of the substrate so that a thickness of the substrate becomes not more than 400 μm, and
 wherein the second surface is one of the following: a processed surface formed by the processing; and a surface including an electrode formed on the processed surface. 
 
     
     
         23 . The method according to  claim 17 , wherein the step of forming the substrate product comprises polishing the substrate so that a thickness of the substrate becomes not less than 50 μm and not more than 100 μm, and
 wherein the second surface is one of the following: a polished surface formed by the polishing; and a surface including an electrode formed on the polished surface. 
 
     
     
         24 . The method according to  claim 17 , wherein the scribing is carried out using a laser scriber, and
 wherein the scribing forms a scribed groove, and a length of the scribed groove is shorter than a length of an intersecting line between the first surface and an a-n plane defined by the normal axis and the a-axis of the hexagonal group-III nitride semiconductor.   
     
     
         25 . The method according to  claim 17 , wherein the semipolar principal surface is any one of {20-21} plane, {10-11} plane, {20-2-1} plane, and {10-1-1} plane. 
     
     
         26 . The method according to  claim 17 , wherein the substrate comprises any one of GaN, AlGaN, AlN, InGaN, and InAlGaN.