Semiconductor device, fabrication method of the semiconductor devices

A method for fabricating a semiconductor device, the method comprising:

• forming a buffer layer, containing a group-III-V compound, on a substrate formed of Y3Al5O12;
• and
• forming a group-III nitride semiconductor layer on the buffer layer,
• wherein the forming the buffer layer includes forming a nucleation layer made of a group-III element in at least a part on the substrate,
• wherein the substrate is a polycrystalline substrate of a plurality of surface orientations.

A semiconductor device comprising:

• a substrate formed of Y3Al5O12;
• and
• a buffer layer, containing a group-III-V compound, formed on the substrate;
• and
• a group-III nitride semiconductor layer formed on the buffer layer,
• the buffer layer including:
• a nucleation layer, made of a group-III element, formed on the substrate;
• and
• a group-III-V compound layer formed on the nucleation layer,
• wherein the substrate is a single-crystal substrate of any of surface orientations (100) and (110) or a polycrstalline substrate of a plurality of surface orientations.