Iii-n epitaxial device structures on free standing silicon mesas

A semiconductor device, comprising:

• a semiconductor structure including:
• a mesa comprising a first crystal, the first crystal comprising silicon;
• a second crystal comprising a first III-N material, the second crystal over a top surface of the mesa with a c-axis of the second crystal substantially orthogonal to the top surface, the second crystal comprising a peripheral region that extends laterally beyond a sidewall of the mesa;
• and
• a second III-N material over the first III-N material, the second III-N material having a composition different than that of the first III-N material;
• and
• one or more device terminals coupled to the semiconductor structure.

A method of forming a semiconductor device structure, the method comprising:

• forming a mesa comprising a first crystal in a first region of a substrate, the first crystal comprising silicon;
• epitaxially growing a second crystal comprising a first III-N material with the c-axis of the second crystal substantially orthogonal to a top surface of the mesa;
• performing a lateral epitaxial overgrowth (LEO) of the second crystal until a sidewall of the second crystal extends laterally beyond a sidewall of the mesa;
• and
• epitaxially growing a second III-N material from at least a (0001) surface of the second crystal, or a (000-1) surface of the second crystal.