Theoretical comparison of electron real-space transfer in classical and quantum two-dimensional heterostructure systems

Abstract

We present a comparison of the effect of real-space transfer on the electron drift velocities in both classical heterostructure systems, those in which spatial quantization effects do not occur, and in two-dimensional heterostructure systems using an ensemble Monte Carlo simulation. The calculations for the two-dimensional system are based on a first-principles formulation of electron transport in a triangular quantum well system using an ensemble Monte Carlo code tailored to include the basic physics of two-dimensional systems. In addition, we present an analysis, again based on a complete ensemble Monte Carlo simulation, of real-space transfer from classical systems, ones in which no two-dimensional gas is formed at the heterointerface. Electron drift velocities within the classical system greater than that possible in the constitutive bulk materials are thwarted by either real-space transfer out of the high mobility material into the adjacent low mobility material or k-space transfer within the narrow gap material itself. In contrast, higher electron drift velocities than that achievable in the bulk occur in a system in which two-dimensional effects are present. In this case, when the electrons are confined within the two-dimensional gas, their corresponding drift velocities are somewhat larger than within the bulk three-dimensional system. We conclude that in electronic devices in which the electric field is applied parallel to the heterostructure layers, that the highest steady-state electron velocities are achieved for transport within the two-dimensional gas. In structures in which either a two-dimensional system is not present or the carriers all reside outside of the quantized states, the steady-state electron drift velocity is always less than or equal to the corresponding velocity in the bulk material due to the combined actions of real-space and k-space transfer.