Current instability in power HEMTs

We present an experimental and theoretical study of current instability in an Al 0.23 Ga 0.77 As/In 0.23 Ga 77 As n-channel delta-doped pseudomorphic high electron-mobility transistor (HEMT). Monte Carlo simulations of the device indicated that it was vulnerable to the formation of unusual `transverse' Gunn dipoles which caused sudden reductions in the drain current. These dipoles were also responsible for a significant number of impact ionization events at higher drain potentials causing a subsequent upturn in the drain current. Our experimental observations of a similar device are in excellent qualitative and good quantitative agreement with our theoretical predictions and so provide compelling evidence for the existence of Gunn instabilities in HEMTs.