LOW-TEMPERATURE MOBILITY OF PHOTOEXCITED ELECTRONS IN ALXGA1-XAS CONTAINING DX CENTERS

An accurate analysis of the electron mobility versus temperature has been performed in Si-doped AlxGa1-xAs samples grown by molecular-beam epitaxy. Mobility data relating to different electron mean energies and fractions of occupied DX centers were obtained by selecting different free-electron densities by low-temperature photoexcitation. Using suitable values for the acceptor density and the alloy scattering potential, a fair fitting of the experimental data was achieved within both negative-U and positive-U models for the DX center. The crucial role of the compensation by acceptor impurities is evidenced to require agreement with experimental data in the positive-U approach. Discrepancies between calculated and experimental mobility-versus-temperature curves are observed for low free-electron densities. They are tentatively explained as being due to electrons in an impurity band originated by the shallow effective-mass state and related to the GAMMA-minimum of the conduction band.