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 (CHFET) 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. The anisotype PFET also uses a non-alloyed graded InGaAs/GaAs ohmic contacts that are stable to temperature as high as 550 degrees C. With AlGaAs composition of x=0.3, and a thin AlAs spacer of 60AA, 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 mu m PFETs, high reverse breakdown voltages, 9-10 V, and low capacitance. Microwave S-parameter characterization resulted in F/sub t/ of 5 GHz for a 1*50 mu m PFET.<>