Model of Γ to X transition in thermally activated tunnel currents across AlxGa1−xAs single barriers

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Abstract
A theoretical study of thermally activated currents across AlxGa1−xAs barriers is presented, where x is varied from zero to one. By increasing the Al content, AlxGa1−xAs changes from a direct to an indirect band‐gap semiconductor. Previous experiments on activated transport have shown that this crossover strongly affects the transport properties. However, usually these experiments are analyzed in terms of the classical Richardson law, which completely fails to explain the prefactor for high Al concentrations which drops by three orders of magnitude. A model is presented that describes the transport by considering two competing channels, one via the Γ minimum and the other via the longitudinal X minimum. The current flow through each channel is evaluated by calculating the transmission coefficient separately for the Γ and X barriers. This model gives new insights into the interpretation of the experimentally measured activation energy and the prefactor.