New evidence for velocity overshoot in a 200 nm pseudomorphic HEMT

It is believed that significant velocity overshoot effects are responsible for the high performance oi pseudomorphic HEMTs (PsHEMTs). The overshoot is associated with the low effective mass in the InGaAs channel and the large Gamma-L separation. Average channel electron velocities well in excess of 3.0 x 10(7) cm/s have been predicted in Monte-Carlo PsHEMT simulations. However, average electron velocities extracted from transconductance measurements of such devices are much lower, typically in the range 1.5-2.0 x 10(7) cm/s. In this paper we analyse real device measurements by using Monte-Carlo and drift diffusion simulations. We show clear evidence that the average velocity in the channel of a 200 nm PsHEMT fabricated in the Nanoelectronics Research Centre of Glasgow University exceeds 3.0 x 10(7) cm/s. Copyright (C) 1996 Elsevier Science Ltd.