The transport properties of AlGaAs/GaAs/AlGaAs heterostructures with doped GaAs quantum well have been investigated by means of an ensemble Monte Carlo method. The model accounts for nonparabolicity, size quantization in all valleys, and degeneracy. The influence of doping profile, density of donors and electrons, well width, and temperature are discussed. Both steady state and transient transport have been studied, and the possibility of strong velocity overshoot has been demonstrated. The electron velocity may be strongly influenced by the spatial distribution of impurities. The choice of a doping plane located at one edge of the well allows for obtaining the highest values of mobility, static peak velocity, and maximum transient velocity. At high fields, some parasitic conduction takes place in the barriers and the transport properties are strongly affected by the characteristics of the AlGaAs layers.

We propose a method for determining diffusion coefficients in degenerate semiconductors from an ensemble Monte Carlo simulation. The basic idea is that what is relevant for this problem is not the whole electron distribution function, but its perturbation in response to an addition of “excess carriers.” Starting from the Boltzmann transport equation, we derive the equation of evolution for this “excess electron distribution function.” We propose an interpretation in terms of scattering events suffered by particles, allowing one to solve the problem by Monte Carlo simulation. We simulate two sets of carriers, coupled by an “exchange scattering” mechanism which is properly defined. The first set represents the uniform background density in the semiconductor, whereas the second one represents the excess carriers. Only the latter is used for calculating diffusion coefficients. This method is applied to a highly degenerate two-dimensional electron gas in a doped GaAs quantum well. The diffusivity-field characteristics are calculated and discussed.

This paper presents a Monte Carlo study of diffusion coefficients in two-dimensional electron gas (TDEG) in III-V heterostructures. The model accounts for the quantization of all valleys and for non-parabolicity. The diffusion coefficients are determined by the spreading of a narrow pulse of carriers drifting along the interface. Two kinds of heterostructures have been considered: AlGaAs/InGaAs/AlGaAs and the AlInAs/InGaAs/AlInAs lattice matched on InP. The diffusion coefficient-field characteristics at 77 K temperature have been extensively studied. Large deviations from the Einstein relation have been observed, even at low-fields. The longitudinal diffusion coefficient is shown to be strongly field dependent and may reach high values for fields around 1 kV cm −1 . Its evolution is explained by the behaviour of scattering rates, especially for impurity and phonon scattering.

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