True Mobilities in Semi-Insulating O- and Cr-Doped GaAs

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It is well known that an analysis of the magnetic field dependences of the resistivity ρ and Hall coefficient R, in nearly intrinsic material, will uniquely yield μ n, μ p, n, and p as long as single -carrier magnetic field dependences are not important. Unfortunately, recent data indicate that such effects are often important in semi-insulating GaAs and thus a new approach is necessary. We suggest an approach that requires only the usual, low field Hall effect and resistivity parameters, R0, and ρ0, but that also assumes knowledge of the intrinsic carrier concentration n¡, and the hole mobility μ p as a function of the electron mobility, i.e. μ p = f(μ n).We describe analyses which yield ni≏(2.6±0.5)×106 cm-3, and a tentative relationship for μ p namely, μ -1p ≏ 9×10-4 + 13μ -1n . Curves of μ n versus R0/ρ 0, with ρ 0 as a parameter, are calculated by using these relationships. For ρ 0 ≤4×106 Ω-cm, the only solutions are μ n ≈ R0/ρ 0 which means that simple Hall measurements will suffice for nearly all O-doped and undoped semi-insulating GaAs. For higher ρ 0, the solutions are double-valued, and means of selecting the proper solution are discussed. A simple compensation-distribution model is presented which yields the positions of the ‘O’ and Cr energy levels.KeywordsHall CoefficientMagnetic Field DependenceConductive SampleMixed ConductionIntrinsic Carrier ConcentrationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.