Channel-buffer (substrate) interface phenomena in GaAs MESFETs fabricated by molecular-beam epitaxy

A fundamental understanding of the channel-buffer (substrate) interface is obtained from an experimental and theoretical investigation of long-channel GaAs MESFETs fabricated by molecular-beam epitaxy (MBE). A low-field channel pinchoff mechanism is studied in which the carrier concentration in the near-pinchoff regime is obtained from an exact solution of Poisson's equation in such a way as to conserve the total charge in the entire device. One the basis of these calculations it is shown that resolution of the order of a Debye length is feasible in the determination of the impurity profile in the vicinity of homojunction interfaces from the conventional capacitance-voltage profiling technique. The threshold-voltage dependence on the semiconductor crystal lattice temperature indicates that steady-state carrier trapping and accumulation of operation. The variations of the threshold voltage and negative charge in donor-like states at the channel-buffer (substrate) interface play a detrimental role in both the linear and saturated regimes of device gate capacitance with substrate bias are consistent with each other and suggest that a significant reduction in the channel charge occurs with increased reverse bias on the substrate.>