The role of impurity band conduction in the low temperature characteristics of thin InSb films grown by molecular beam epitaxy
We report on the temperature-dependent electrical properties of high-quality undoped InSb layers of various thicknesses grown on GaAs(100) substrates by molecular beam epitaxy. The layers are found to be n-type in the measured temperature range (77–297 K). A differential Hall approach was employed to characterize the depth dependence of the electrical properties of the InSb films. The temperature variations of these data were then modelled with the inclusion of conduction through an impurity band, formed by the overlap of the wavefunctions of the dislocation-related donors. These analyses suggest that the contribution of the impurity band is dominant close to the interface even at room temperature, but its effect falls with increasing thickness, until at ~1000 nm, its contribution is only comparable to that of the conduction band at low temperatures. The dislocation donor densities deduced from this modelling follow an approximately reciprocal trend with increasing distance from the interface.