Low-field electron transport mechanism in GaAs MESFETs

Electron transport mechanisms in the vicinity of channel-buffer (substrate) interfaces in GaAS MESFETs are studied at low values of transverse electric field, both theoretically and experimentally. It is shown that considerable degradation in the low-field drift mobility occurs in the near-pinchoff regime. Experimental results for long-channel MESFETs fabricated by molecular-beam epitaxy (MBE) exhibit nearly 35% degradation of the drift mobility in that regime. Scattering calculations based on the steady-state Boltzmann transport equation are in good agreement with the measured mobility data and suggest that electrons are predominantly scattered from the steep channel walls and localized states at the channel-buffer interface. The latter is atomically abrupt and nearly free of contamination in these devices. The localized states are hypothesized to have originated from changes in the growth conditions that might occur during the interface formation in the ultrahigh-vacuum environment of the MBE system