Electron scattering by a spatially correlated system of DX charges has been described using the formalsim of composition waves. The matrix element for the scattering rate is given through an I(Q) interference function (Q=scattering vector) containing pair correlation functions ɛ(p) defined at the p lattice vectors. The ɛ(p) are able to describe long-range as well as short-range order and they are simply related to short-range order correlation functions given in the literature. The method is developed for scattering centers having equal charges; the case of positively and negatively charged impurities present together is briefly discussed. A comparison between the two extreme cases of randomly distributed scattering centers and of centers arranged in a superlattice suggests, for intermediate cases, an I(Q) given by an array of Gaussian shaped functions with common dispersion σ, centered on the reciprocal nodes of a virtual superlattice. On this basis, experimental mobility data for Si-doped Al0.25Ga0.75As samples prepared by molecular beam epitaxy have been analyzed and discussed. Data refer to isothermal electron capture transients into DX centers, as well as to steady-state measurements taken for different free electron densities under a persistent photoconductivity regime. It has been confirmed that the initial stage of the capture process takes place together with increasing order in the scattering center distribution (decreasing σ), whereas the contrary happens during the final stage (increasing σ).
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