Semiconductor substrate, semiconductor device and method for fabricating the same

A semiconductor substrate comprising:

• a SiC bulk substrate;
• and
• an epitaxially grown layer of SiC provided over said SiC bulk substrate,
• wherein said epitaxially grown layer has a structure in which a first SiC layer and a second SiC layer including a carrier dopant in a concentration higher than in said first SiC layer and having a thickness smaller than said first SiC layer are alternately deposited, and
• assuming that said first SiC layer has a thickness t and that irregularities formed on a top face of said first SiC layer have a step height h, a ratio h/t between the step height and the thickness of said first SiC layer is in a range from 10−6 to 10−1, and an average step height is 5 nm or less.

A semiconductor device comprising:

• a bulk substrate of a compound semiconductor;
• and
• a first compound semiconductor layer epitaxially grown on a top face of said bulk substrate,
• wherein said first compound semiconductor layer includes a second compound semiconductor layer in which carriers move or pass during operation, and assuming that said second compound semiconductor layer has a thickness t and that irregularities formed on a top face of said second compound semiconductor layer have a step height h, a ratio h/t between the step height and the thickness of said second semiconductor layer is in a range from 10−6 to 10−1, and the step height is 10 nm or less.