ANISOTYPE-GATE SELF-ALIGNED P-CHANNEL HETEROSTRUCTURE FIELD-EFFECT TRANSISTORS

A new self-aligned p-channel HFET structure was evaluated for application to complementary HFET circuits. The AlGaAs/InGaAs HFET structure uses an anisotype graded n+ InGaAs/GaAs semiconductor gate to enhance the barrier height of the FET, resulting in a significant reduction in gate leakage current at low voltages. With AlGaAs composition of x = 0.3, and a thin AlAs spacer of 60 angstrom, leakage current was reduced by a factor of about 1000 at gate voltage of 1 V, when compared to AlGaAs/InGaAs HIGFET of aluminum content x = 0.75. The anisotype PFET maintains high device transconductance, typically 50 mS/mm for 1.3 x 10 mum PFET's, high reverse breakdown voltages 9-10 V, and low capacitance. Microwave S-parameter characterization resulted in F(t) of 5 GHz for a 1 x 50 mum PFET.