US Patent 9786743 Semiconductor device with electron supply layer

A semiconductor device includes a semiconductor stacked structure including at least an electron transit layer and an electron supply layer over a substrate. The electron supply layer includes a first portion and second portions sandwiching the first portion, and the first portion has a higher energy of a conduction band than that of the second portion, and includes a doped portion doped with an n-type impurity and undoped portions that sandwich the doped portion and are not doped with an impurity.