Patent ID: 7199408

Claim:
A semiconductor multilayer structure comprising: a predetermined base; an underlying layer formed on said base; and a group of semiconductor layers formed on said underlying layer and including a first semiconductor layer made of a first group-III nitride, a second semiconductor layer made of AlN which is a second group-III nitride, and a third semiconductor layer made of a third group-Ill nitride containing at least Al, said first, second and third semiconductor layers being stacked together in the order named as seen from the underlying layer side, said underlying layer being made of a fourth group-III nitride containing at least Al and having a higher Al mole fraction in all of the group-III elements than does said first group-III nitride, said semiconductor multilayer structure having a sheet carrier density of not less than 5×10 12 /cm 2 and an electron mobility of not less than 20000 cm 2 /V·s at a temperature of 15 K.