Persistent photoconductivity in (Al,Ga)As/GaAs modulation doped structures: Dependence on structure and growth temperature

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Abstract
When modulation doped (Al,Ga)As/GaAs heterostructures are exposed to light, the interface electron concentration and in most cases the mobility increases substantially for lattice temperatures below ∼100 K. A substantial part of the increase is persistent and attributed to the excitation of electrons from a donor–vacancy complex in the (Al,Ga)As. The change in the free electron concentration in the (Al,Ga)As is calculated using a recently developed model for electron transfer across a modulation doped heterojunction. The persistent increase in the free electron concentration is used as a measure of the trap concentration. The magnitude of the photoconductivity response decreased with increasing growth temperature in the range 580–750 °C. The dependence on Al mole fraction was studied for 0.16≤x≤1.0 and found to be a maximum for x∼0.3.