Quantum transport in mesoscopic devices: Current conduction in quantum wire structures

Abstract

A theory based on the Keldysh formalism is developed to study carrier transport in inhomogeneous quantum effects devices that operate at higher temperatures under large applied bias voltages. The scattering rates due to dissipative processes within devices are estimated self-consistently from the nonequilibrium particle density and the density of states. Unlike many existing models, the present model guarantees the conservation of the current and the number of particles in active devices. We have applied our model to study carrier transport in GaAs quantum wire devices and report several interesting results. It is found that a sudden increase in the polar-optical phonon scattering rates may result in a negative current at some critical energies when the bias voltage is positive. At low temperatures, the conductance of quantum wires shows quantized steps as a function of the applied bias voltage. Moreover, a negative differential conductance (NDC) is observed in the current–voltage characteristics of devices containing a single tunnel barrier. Such NDC disappears in the presence of strong inelastic scattering. Our results show that it is not possible to simulate many of the novel transport effects without explicitly incorporating the appropriate energy and the position dependences of the scattering rates.