Group-iii nitride semiconductor laser device, method of fabricating group-iii nitride semiconductor laser device, and epitaxial substrate

Abstract

A III-nitride semiconductor laser device is provided with a laser structure and an electrode. The laser structure includes a support base which comprises a hexagonal III-nitride semiconductor and has a semipolar primary surface, and a semiconductor region provided on the semipolar primary surface. The electrode is provided on the semiconductor region. The semiconductor region includes a first cladding layer of a first conductivity type GaN-based semiconductor, a second cladding layer of a second conductivity type GaN-based semiconductor, and an active layer provided between the first cladding layer and the second cladding layer. The laser structure includes first and second fractured faces intersecting with an m-n plane defined by the m-axis of the hexagonal III-nitride semiconductor and an axis normal to the semipolar primary surface. A laser cavity of the III-nitride semiconductor laser device includes the first and second fractured faces. An angle ALPHA between the normal axis and the c-axis of the hexagonal III-nitride semiconductor is in the range of not less than 45 degrees and not more than 80 degrees or in the range of not less than 100 degrees and not more than 135 degrees. The laser structure includes a laser waveguide extending above the semipolar primary surface, and the laser waveguide extends in a direction of a waveguide vector directed from one to another of the first and second fractured faces. A c-axis vector indicating a direction of the c-axis of the hexagonal III-nitride semiconductor includes a projected component parallel to the semipolar primary surface and a vertical component parallel to the normal axis. An angle difference between the waveguide vector and the projected component is in the range of not less than −0.5 degrees and not more than +0.5 degrees.

1 . A III-nitride semiconductor laser device comprising:
 a laser structure including a support base and a semiconductor region, the support base comprising a hexagonal III-nitride semiconductor and having a semipolar primary surface, and the semiconductor region being provided on the semipolar primary surface of the support base; and   an electrode provided on the semiconductor region of the laser structure,   the semiconductor region comprising a first cladding layer of a first conductivity type GaN-based semiconductor, a second cladding layer of a second conductivity type GaN-based semiconductor, and an active layer 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 an axis normal to the semipolar primary surface,   the active layer comprising a GaN-based semiconductor layer,   a c-axis of the hexagonal III-nitride semiconductor of the support base being inclined at an angle ALPHA with respect to the normal axis toward an m-axis of the hexagonal III-nitride semiconductor,   the laser structure comprising first and second fractured faces, the first and second fractured faces intersecting with an m-n plane, the m-n plane being defined by the normal axis and the m-axis of the hexagonal III-nitride semiconductor,   a laser cavity of the III-nitride semiconductor laser device comprising the first and second fractured faces,   the laser structure comprising first and second surfaces, the first surface being 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,   the angle ALPHA being in one of a range of not less than 45 degrees and not more than 80 degrees and a range of not less than 100 degrees and not more than 135 degrees,   the laser structure comprising a laser waveguide on the semipolar primary surface of the support base, and the laser waveguide extending in a direction of a waveguide vector directed from one to another of the first and second fractured faces,   a c-axis vector indicating a direction of the c-axis of the hexagonal III-nitride semiconductor and including a projected component parallel to the semipolar primary surface and a vertical component parallel to the normal axis, and   an angle difference between the waveguide vector and the projected component being in a range of not less than −0.5 degrees and not more than +0.5 degrees.   
     
     
         2 . A III-nitride semiconductor laser device comprising:
 a laser structure including a support base and a semiconductor region, the support base comprising a hexagonal III-nitride semiconductor and having a semipolar primary surface, and the semiconductor region being provided on the semipolar primary surface of the support base; and   an electrode provided on the semiconductor region of the laser structure,   the semiconductor region including a first cladding layer of a first conductivity type GaN-based semiconductor, a second cladding layer of a second conductivity type GaN-based semiconductor, and an active layer 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 axis normal to the semipolar primary surface,   the active layer comprising a GaN-based semiconductor layer,   a c-axis of the hexagonal III-nitride semiconductor of the support base being inclined at an angle ALPHA with respect to the normal axis toward the m-axis of the hexagonal III-nitride semiconductor,   the laser structure including first and second fractured faces, the first and second fractured faces intersecting with an m-n plane, the m-n plane being defined by the normal axis and an m-axis of the hexagonal III-nitride semiconductor,   a laser cavity of the III-nitride semiconductor laser device including the first and second fractured faces,   the laser structure including first and second surfaces, the first surface being 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,   the angle ALPHA is in one of a range of not less than 45 degrees and not more than 80 degrees and a range of not less than 100 degrees and not more than 135 degrees,   the laser structure including a waveguide on the semipolar primary surface of the support base, the waveguide extending in a direction of a waveguide vector directed from one to another of the first and second fractured faces,   the laser structure exhibiting a streaky emission pattern in a fluorescence microscope image based on photoexcitation with a mercury lamp, the streaky emission image extending in a direction of a predetermined axis, and   an angle difference between the waveguide vector and a direction orthogonal to the predetermined axis being in a range of not less than −0.5 degrees and not more than +0.5 degrees.   
     
     
         3 . The III-nitride semiconductor laser device according to  claim 1 , wherein the angle between the normal axis and the c-axis of the hexagonal III-nitride semiconductor is in one of a range of not less than 63 degrees and not more than 80 degrees and a range of not less than 100 degrees and not more than 117 degrees. 
     
     
         4 . The III-nitride semiconductor laser device according to  claim 1 , wherein a thickness of the support base is not more than 400 μm. 
     
     
         5 . The 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. 
     
     
         6 . The III-nitride semiconductor laser device according to  claim 1 , wherein laser light from the active layer is polarized in a direction of the a-axis of the hexagonal III-nitride semiconductor. 
     
     
         7 . The III-nitride semiconductor laser device according to  claim 1 , wherein light in an LED mode in the III-nitride semiconductor laser device includes a polarization component I 1  in a direction of an a-axis of the hexagonal III-nitride semiconductor, and a polarization component I 2  in a direction of the projected c-axis of the hexagonal III-nitride semiconductor onto the primary surface, and the polarization component Il is greater than the polarization component I 2 . 
     
     
         8 . The III-nitride semiconductor laser device according to  claim 1 , wherein the semipolar primary surface is a surface with a slight slant toward an m-plane in a range of not less than −4 degrees and not more than +4 degrees with respect to any one semipolar plane of a {20-21} plane, a {10-11} plane, a {20-2-1} plane, and a {10-1-1} plane. 
     
     
         9 . The III-nitride semiconductor laser device according to  claim 1 , wherein the semipolar primary surface is one of a {20-21} plane, a {10-11} plane, a {20-2-1} plane, and a {10-1-1} plane. 
     
     
         10 . The 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 . 
     
     
         11 . The III-nitride semiconductor laser device according to  claim 1 , wherein the support base comprises any one of GaN, AlGaN, MN, InGaN, and InAlGaN. 
     
     
         12 . The 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. 
     
     
         13 . The 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. 
     
     
         14 . The 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. 
     
     
         15 . The III-nitride semiconductor laser device according to  claim 1 , wherein
 an end face of the support base and an end face of the semiconductor region are exposed in each of the first and second fractured faces, and   an angle between an end face of the active layer in the semiconductor region and a reference plane perpendicular to the m-axis of the support base of the hexagonal nitride semiconductor is an angle in a range of not less than (ALPHA−5) degrees and not more than (ALPHA+5) degrees on a first plane defined by the c-axis and the m-axis of the III-nitride semiconductor.   
     
     
         16 . The III-nitride semiconductor laser device according to  claim 1 , wherein the angle difference is in a range of not less than −0.3 degrees and not more than +0.3 degrees. 
     
     
         17 . A method of fabricating a III-nitride semiconductor laser device, the method comprising steps of
 preparing a substrate, the substrate comprising a hexagonal III-nitride semiconductor and having a semipolar primary surface;   forming a substrate product having a laser structure, an anode electrode and a cathode electrode, the laser structure including a semiconductor region and the substrate, and the semiconductor region being formed on the semipolar primary surface;   scribing a first surface of the substrate product in part in a direction of an a-axis of the hexagonal 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 a surface 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 extending from the first surface to the second surface and being made by the breakup,   the first and second end faces constituting a laser cavity of the III-nitride semiconductor laser device,   the anode electrode and the cathode electrode being formed on the laser structure,   the semiconductor region including a first cladding layer of a first conductivity type GaN-based semiconductor, a second cladding layer of a second conductivity type GaN-based semiconductor, and an active layer 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 primary surface,   the active layer comprising a GaN-based semiconductor layer,   a c-axis of the hexagonal III-nitride semiconductor of the substrate being inclined at an angle ALPHA with respect to the normal axis toward the m-axis of the hexagonal III-nitride semiconductor;   the first and second end faces intersecting with an m-n plane, the m-n plane being defined by an m-axis of the hexagonal III-nitride semiconductor and the normal axis,   the angle ALPHA being in one of a range of not less than 45 degrees and not more than 80 degrees and a range of not less than 100 degrees and not more than 135 degrees,   the laser structure comprising a laser waveguide, the laser waveguide extending on the semipolar primary surface of the substrate, and the laser waveguide extending in a direction of a waveguide vector directed from one to another of the first and second fractured faces,   a c-axis vector indicating a direction of the c-axis of the hexagonal III-nitride semiconductor and including a projected component parallel to the semipolar primary surface and a vertical component parallel to the normal axis,   an angle difference between the waveguide vector and the projected component is in a range of not less than −0.5 degrees and not more than +0.5 degrees,   the semiconductor region of the substrate product comprising a mark indicative of a direction of the a-axis of the hexagonal III-nitride semiconductor,   in the step of forming the substrate product, a direction of the laser waveguide being determined based on the mark.   
     
     
         18 . The method according to  claim 17 , wherein the angle difference is in a range of not less than −0.3 degrees and not more than +0.3 degrees. 
     
     
         19 . The method according to  claim 17 , wherein the angle ALPHA is in one of a range of not less than 63 degrees and not more than 80 degrees and a range of not less than 100 degrees and not more than 117 degrees. 
     
     
         20 . The method according to  claim 17 , wherein
 in the step of forming the substrate product, processing such as slicing or grinding of the substrate is performed so that a thickness of the substrate becomes not more than 400 μm, and   the second surface includes one of a processed surface made by the processing and a surface including an electrode formed on the processed surface.   
     
     
         21 . The method according to  claim 17 , wherein
 in the step of forming the substrate product, the substrate is polished so that a thickness of the substrate becomes not less than 50 μm and not more than 100 μm, and   the second surface includes one of a polished surface formed by the polishing and a surface including an electrode formed on the polished surface.   
     
     
         22 . The method according to  claim 17 , wherein
 the scribing is carried out using a laser scriber,   the scribing forms a scribed groove, and a length of the scribed groove is shorter than a length of a line of intersection between the first surface and an a-n plane defined by the a-axis of the hexagonal III-nitride semiconductor and the normal axis.   
     
     
         23 . The method according to  claim 17 , wherein the semipolar primary surface is any one of a {20-21} plane, a {10-11} plane, a {20-2-1} plane, and a {10-1-1} plane. 
     
     
         24 . The method according to  claim 17 , wherein an end face of the active layer in each of the first and second end faces makes an angle with respect to a reference plane in a range of not less than (ALPHA−5) degrees and not more than (ALPHA+5) degrees on a plane defined by the c-axis and the m-axis of the hexagonal III-nitride semiconductor, and the reference plane is perpendicular to the m-axis of the substrate of the hexagonal nitride semiconductor. 
     
     
         25 . The method according to  claim 17 , wherein the substrate comprises any one of GaN, AlN, AlGaN, InGaN, and InAlGaN. 
     
     
         26 . The method according to  claim 17 , wherein the substrate comprises an orientation flat indicative of an a-plane of the hexagonal III-nitride semiconductor, and the mark comprises the orientation flat. 
     
     
         27 . The method according to  claim 17 , wherein the substrate comprises a cleaved facet along an a-plane of the hexagonal III-nitride semiconductor and the mark includes the cleaved facet. 
     
     
         28 . The method according to  claim 17 , wherein in the step of forming the substrate product, a laser beam is applied to the substrate product to form laser marks arrayed in a direction of the a-axis of the hexagonal III-nitride semiconductor, and the mark includes an array of the laser marks. 
     
     
         29 . The method according to  claim 28 , wherein the laser structure exhibits a streaky emission image extending in a direction of a predetermined axis in a fluorescence microscope image created by photoexcitation with a mercury lamp,
 a direction of the array of the laser marks is determined based on a direction of the predetermined axis of the streaky emission image, and   an angle difference between the waveguide vector and a direction orthogonal to the predetermined axis is in a range of not less than −0.5 degrees and not more than +0.5 degrees.   
     
     
         30 . An epitaxial substrate for a III-nitride semiconductor laser device, comprising:
 a substrate having a semipolar primary surface of a hexagonal III-nitride semiconductor; and   a semiconductor laminate provided on the semipolar primary surface of the substrate,   the semiconductor laminate including a semiconductor region for a laser structure;   the semiconductor region comprising a first cladding layer of a first conductivity type GaN-based semiconductor, a second cladding layer of a second conductivity type GaN-based semiconductor, and an active layer 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 an axis normal to the semipolar primary surface;   the active layer comprising a GaN-based semiconductor layer;   a c-axis of the hexagonal III-nitride semiconductor of the substrate being inclined at an angle ALPHA with respect to the normal axis toward an m-axis of the hexagonal III-nitride semiconductor;   the angle ALPHA between the normal axis and the c-axis of the hexagonal III-nitride semiconductor being in one of a range of not less than 45 degrees and not more than 80 degrees and a range of not less than 100 degrees and not more than 135 degrees;   the semiconductor laminate comprising a structure that extends along a reference axis indicative of a direction of an a-axis of the hexagonal III-nitride semiconductor.   
     
     
         31 . The epitaxial substrate according to  claim 30 , wherein the structure has a length of not less than 230 μm in the direction of the a-axis. 
     
     
         32 . The epitaxial substrate according to  claim 30 , wherein the structure have a surface morphology extending in the direction of the a-axis on a top surface of the semiconductor laminate. 
     
     
         33 . The epitaxial substrate according to  claim 30 , wherein the structure includes a depression on the top surface of the semiconductor laminate. 
     
     
         34 . The epitaxial substrate according to  claim 30 , wherein the structure is provided at a position of a stacking fault arriving at a top surface of the semiconductor laminate. 
     
     
         35 . The epitaxial substrate according to  claim 30 , wherein the structure makes an angle difference with respect to the direction of the a-axis in a range of not less than −0.5 degrees and not more than +0.5 degrees. 
     
     
         36 . The epitaxial substrate according to  claim 30 , wherein the structure makes the angle difference with respect to the direction of the a-axis in a range of not less than −0.3 degrees and not more than +0.3 degrees. 
     
     
         37 . The epitaxial substrate according to  claim 30 , wherein the structure comprise a defect region observed as a dark region in an emission image based on excitation with a mercury lamp. 
     
     
         38 . The epitaxial substrate according to  claim 37 , wherein a long side in the dark region in the emission image extends in the direction of the reference axis, and the long side has a length of not less than 230 μm. 
     
     
         39 . The epitaxial substrate according to  claim 37 , wherein an angle difference between the long side and the direction of the a-axis is in a range of not less than −0.5 degrees and not more than +0.5 degrees. 
     
     
         40 . The epitaxial substrate according to  claim 37 , wherein an angle difference between the long side and the direction of the a-axis is in a range of not less than −0.3 degrees and not more than +0.3 degrees. 
     
     
         41 . The epitaxial substrate according to  claim 37 , wherein the dark region comprises a crystal defect in the active layer. 
     
     
         42 . The epitaxial substrate according to  claim 37 , wherein a cross-sectional shape in a plane perpendicular to the a-axis is hexagonal at least in part of the crystal defect. 
     
     
         43 . The epitaxial substrate according to  claim 37 , wherein the dark region has a feature to expand by a thermal treatment at a high temperature of not less than 800 degrees Celsius. 
     
     
         44 . A method of fabricating a III-nitride semiconductor laser device, the method comprising the steps of:
 preparing an epitaxial substrate,
 the epitaxial substrate which includes a support base comprising a hexagonal III-nitride semiconductor and having a semipolar primary surface, and a semiconductor laminate provided on the semipolar primary surface of the support base, 
 the semiconductor laminate including a semiconductor region for a laser structure, 
 the semiconductor region including a first cladding layer of a first conductivity type GaN-based semiconductor, a second cladding layer of a second conductivity type GaN-based semiconductor, and an active layer 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 primary surface, 
 the active layer comprising a GaN-based semiconductor layer, 
 a c-axis of the hexagonal III-nitride semiconductor of the support base being inclined at an angle ALPHA with respect to the normal axis toward an m-axis of the hexagonal III-nitride semiconductor, 
 the angle ALPHA between the normal axis and the c-axis of the hexagonal III-nitride semiconductor being in one of a range of not less than 45 degrees and not more than 80 degrees and a range of not less than 100 degrees and not more than 135 degrees, 
 the semiconductor laminate including a structure that extends along a reference axis indicating an a-axis of the hexagonal III-nitride semiconductor; 
   forming a substrate product with an anode electrode and a cathode electrode, using the epitaxial substrate;   forming a scribed mark on the substrate product, a direction of the scribed mark being defined with reference to the structure; and   performing breakup of the substrate product by press on the substrate product to form another substrate product and a laser bar,   the laser bar including first and second end faces formed by the breakup;   the first and second end faces constituting a laser cavity of the III-nitride semiconductor laser device;   the substrate product comprising a laser structure, the laser structure including the substrate with the semipolar primary surface of the hexagonal III-nitride semiconductor, and the semiconductor region being formed on the semipolar primary surface;   the anode electrode and the cathode electrode being formed on the laser structure;   the first and second end faces intersecting with an m-n plane, the m-n plane being defined by an m-axis of the hexagonal III-nitride semiconductor and the normal axis.   
     
     
         45 . The method according to  claim 44 , wherein
 the step of forming the substrate product comprises forming an insulating film to cover the semiconductor region of the laser structure;   an aperture of a stripe shape is formed in the insulating film;   a direction of the aperture is defined with reference to the structure in formation of the insulating film;   either one of the anode electrode and the cathode electrode is in contact with the laser structure through the aperture of the insulating film.   
     
     
         46 . The method according to  claim 44 , wherein
 the semiconductor region of the laser structure has a ridge structure;   the ridge structure has a stripe shape;   in formation of the ridge structure, a direction of the stripe shape of the ridge structure is determined with reference to the structure.