Pressure dependence of electron concentration and mobility in GaAs:Si-effects of on-site and inter-site interactions within a system of DX centres

A novel special experimental procedure, where a helium gas pressure cell is employed to vary the hydrostatic pressure at low temperatures, is used to study the freeze-out of carriers on the metastable states of Si donors in GaAs. This technique separates the modifications of the mobility originating from alterations in the band structure from those related to the electron transfer to DX centres. The procedure allows a more precise evaluation of the ability of high-pressure experiments to distinguish between models of positive and negative U for the DX centre. The mobility increase with pressure is theoretically shown to occur for both repulsive (positive U) and attractive (negative U) on-site electron-electron interactions, provided that the inter-site Coulomb interactions are taken into account.