Normally-off Al0.5Ga0.5As heterojunction-gate GaAs f.e.t.

D.C. microwave and large-signal switching properties of a normally-off heterojunction-gate GaAs f.e.t. are reported. The device structure comprises an n-type active channel layer, a p-type Al0.5Ga0.5 As gate layer and a p+-type GaAs contact layer. The gate structure is obtained by selectively etching the p-type GaAs and Al0.5Ga0.5As. Undercutting of the Al0.5Ga0.5 As layer results in a submicrometre gate length, and the resulting p+-GaAs overhang is used to self align the source and the drain with respect to the gate. GaAs f.e.t.s with 0.5 to 0.7¿-long heterojunction gates have exhibited maximum available power gains of about 9 dB at 2 GHz. Large-signal pulse measurements indicate an intrinsic propagation delay of 40 ps with an arbitrarily chosen 100¿ drain load resistance in a 50¿ microstrip circuit.