Semiconductor laser device

A semiconductor laser device, comprising:

• a monocrystalline electrically conductive GaN sub-mount substrate having a crystalline structure including a first crystalline plane and a second crystalline plane, the first crystalline plane being a c-plane and having a normal line direction thereof on a first crystalline axis and the second crystalline plane being an a-plane and having a normal line direction thereof on a second crystalline axis having a higher thermal conductivity than the first crystalline axis;
• a semiconductor laser chip configured to be joined to a side of a first surface of the sub-mount substrate;
• a first joining layer configured to join the semiconductor laser chip to the first surface of the sub-mount substrate;
• a second joining layer configured to join a second surface of the sub-mount substrate to a heatsink;
• and
• an insulating film having a thickness less than 10 um and greater than or equal to 0.2 um and configured to insulate the semiconductor laser chip from the heatsink, and
• the first surface of the sub-mount substrate being offset from the first crystalline plane at an angle between 4 degrees and 20 degrees so as to add a component in a direction of the second crystalline axis which has a higher thermal conductivity as compared to a line normal to the first surface of the sub-mount substrate.