A semiconductor device includes: a substrate; a buffer layer including GaN formed
on the substrate, wherein: surfaces of the buffer layer are c facets of Ga atoms;
a channel layer including GaN or InGaN formed on the buffer layer,wherein: surfaces
of the channel layer are c facets of Ga or In atoms; an electron donor layer including
AlGaN formed on the channel layer, wherein: surfaces of the electron donor layer
are c facets of Al or Ga atoms; a source electrode and a drain electrode formed
on the electron donor layer; a cap layer including GaN or InGaAlN formed between
the source electrode and the drain electrode, wherein: surfaces of the cap layer
are c facets of Ga or In atoms and at least a portion of the cap layer is in contact
with the electron donor layer; and a gate electrode formed at least a portion of
which is in contact with the cap layer.
