Spatial Correlation of Impurity Charges Induced by Coulomb Interactions - Application to DX Centers in GaAs

The electron mobility enhancement observed in heavily doped GaAs under hydrostatic pressure is interpreted in terms of spatial correlation between the donor charges within partially occupied system of impurities induced by strong inter-donor Coulomb interaction. A simple analytic theory is given for both DX$\text{}^{0}$ and DX$\text{}^{-}$ models of the impurity state. The mobility is shown to increase together with pressure in both models. Estimates of the energy of the DX level are strongly perturbed by the inter-donor Coulomb interactions.