Patent ID: 8344421

Claim:
An enhancement mode field effect device comprising: a first active layer composed of a group III-nitride semiconductor layer; a second active layer composed of a group III-nitride barrier layer on the first active layer, wherein the second active layer has a band gap wider than the band gap of the first active layer; one or more overlayers disposed over the second active layer, wherein material composition of at least some of the one or more overlayers, including at least the overlayer closest to the second active layer, is different from material composition of the second active layer, wherein there is a two-dimensional electron gas at or near an interface between the first and second active layers and wherein the two-dimensional electron gas would not be present in the absence of the one or more overlayers; a gate electrode extending through the one or more overlayers and in direct contact with the group III-nitride barrier layer of the second active layer, wherein the two-dimensional gas is not present directly under the gate electrode unless a positive voltage above a predetermined threshold is applied to the gate electrode; and source and drain electrodes in direct contact with a group III-nitride semiconductor layer.