Neutral impurity scattering in AlGaAs

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Abstract
In the alloy system AlGaAs, a crossover from a direct (Γ) to an indirect (X) conduction-band minimum occurs when the AlAs mole fraction approaches 0.45. For AlAs mole fractions greater than about 0.2, the ground-state energy of substitutional donors becomes deep relative to the direct minimum. The donor level achieves a maximum depth of 0.16 eV near the crossover and it is not uncommon to find the donor impurity concentration exceeding the free-electron concentration by a factor of 10 at room temperature and a factor of 20 at lower temperatures. For large impurity to electron ratios and doping levels on the order of 1018/cm3, neutral impurity scattering proves to be the dominant scattering mechanism at all temperatures.