ABSTRACT
Heterostructure transistors, PMODFETs and HBTs are reviewed. The PMODFET, alleviates the DX center problem of the conventional MODFETs and provides an InGaAs channel with superior properties. A MODFET exhibited a power gain of 7.3 dB at 140 GHz and a noise level of 1.4 dB near 90 GHz. As for HBTs, AlGaAs/GaAs, GalnP/GaAs, InP/InGaAs, AlInAs/InGaAs, and SiGe/Si have been exploited. Current gain cut off, ft, and maximum oscillation, fmax, frequencies are about 100 GHz and 200 GHz, respectively. SiGe HBTs exhibited fi’s in excess of 100 GHz with applications in AD converters and PCS. Metal insulator semiconductor structures utilizing Si interface and Si3N4 dielectric layers exhibit inversion field effect transistors.
