The effect of reflecting contacts on high field transport

Abstract

ABSTRACT There has been considerable recent interest in semiconductor device structures which take advantage of high velocity, high field transport. The high electron velocity in devices that take advantage of such transport is degraded if electrons are reflected at collecting contacts. This was demonstrated quantitatively by Brennan and coworkers (1983) who modeled the collecting contact with a constant, arbitrary reflection coefficient. For a real contact, however, the probability of an electron being reflected depends on its energy and momentum. We present a study of the effect of contacts on high field transport by detailed Monte Carlo simulations of transport in an n- region which terminates in an n GaAs/metal contact (Arnold 1987). The details of the Monte Carlo transport simulation method which we employed were reported by Brennan and coworkers (1983a) and in the references contained therein. The contact is modeled as a thin n+ doped region of GaAs, sandwiched between the active region of the device and a contact metal. The potential was found by solving Poisson's Equation for this system in equilibrium. A voltage drop across the device is is added by assuming a constant applied field in the (n-GaAs) active region. The transmission matrix technique has been used to accurately calculate the reflection probability for energies above and below the maximum of the barrier (Kane 1969). Here the matching conditions for the solution of Schroedingers Equation are continuity of the wavefunction ∂ and of the current, i.e., of (1/m*)(∂ψ/∂x), where m is the energy dependent effective mass.