The d.c., microwave, and high-temperature characteristics of Si-doped
MESFETs with and without n(+) ohmic contact layers, Si3N4/GaN MISFETs,
and AIN/GaN HFETs are presented. The highest transconductance and mic
rowave performance were observed for 1 mu m gate-length HFETs. These H
FETs have a transconductance of 45 mS/mm, an f tau of 8 GMz, and an f(
max) of 22 GHz. The Si-doped MESFETs have good pinch-off characteristi
cs at 400 degrees C and are operational at 500 degrees C.