Patent ID: 7800130

Claim:
A normally-off heterojunction semiconductor device comprising: a lower semiconductor layer comprising a first type of semiconducting material; an upper semiconductor layer comprising a second type of semiconducting material that has a larger band gap than the first type of semiconducting material, wherein the upper semiconductor layer is attached to a top surface of the lower semiconductor layer; a first electrode formed on a portion of a top surface of the upper semiconductor layer; a second electrode formed on a different portion of the top surface of the upper semiconductor layer; and a gate electrode electrically connected to the lower semiconductor layer, wherein a conductivity type of the lower semiconductor layer is p-type, an electric potential of the lower semiconductor layer can vary in accordance with an electric potential of the gate electrode, and a two-dimensional electron gas layer is generated at a boundary between the lower semiconductor layer and the upper semiconductor layer when a gate-on voltage is applied to the gate electrode so that the electrons flow between the first electrode and the second electrode via the two-dimensional electron gas layer.