Dependence of mobility on DX-centre configuration in GaAlAs alloy
A combined effect of illumination, pressure and temperature allows the authors to obtain GaAlAs material with different DX-centre configurations populated at different rates. Study of the effects of temperature on Hall effect and resistivity in Si-doped GaAlAs alloy (Al content x=15%) has made it evident that the mobility in the sample in non-equilibrium conditions is not a single-value function of free carrier concentration, and that with increasing carrier concentration the mobility can either decrease or increase, depending on the distribution of DX-centres between different configurations. The observed behaviour can be explained qualitatively within the framework of a multilevel negative-U DX-centre model, if the effects of spatial correlations between DX- and d+ centres are taken into account.