Patent ID: 7663162

Claim:
A compound semiconductor device comprising: a lower electron transport layer made of compound semiconductor material; a lower electron supply layer disposed over the lower electron transport layer and made of compound semiconductor material doped to n-type and having an electron affinity smaller than an electron affinity of the lower electron transport layer; an upper electron transport layer disposed over the lower electron supply layer and made of compound semiconductor material having a doping concentration lower than a doping concentration of the lower electron supply layer or non-doped compound semiconductor material; an upper electron supply layer disposed over the upper electron transport layer and made of n-type compound semiconductor material having an electron affinity smaller than an electron affinity of the upper electron transport layer; a source electrode and a drain electrode disposed over the upper electron supply layer at a distance from each other and being in ohmic contact with the lower electron transport layer and the upper electron transport layer; and a gate electrode disposed over the upper electron supply layer between the source electrode and the drain electrode.