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

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.