Temperature dependence of the Schottky barrier in Al/AlGaAs metal-semiconductor junctions

The dependence on temperature and alloy composition of the Schottky barrier height of Al on Al_xGa_1-xAs metal-semiconductor junctions for n- and p-type substrates and 0<x<1 is reported. All the structures were grown by molecular beam epitaxy. The compositional dependence of the barrier heights is the same as that of the band offsets in GaAs/GaAlAs heterojunctions. The barrier height for the p-type substrates is practically independent of temperature over the whole composition range, while for the n-type substrates the temperature change of the Schottky barrier follows that of the energy gap. This observation questions validity of the class of models of the Schottky barrier formation based on the concept of a neutrality level. Such behavior can, however, be reconciled if localized defects, whose ground-state wave function is of a bonding type are the source of the Fermi-level pinning at the interface.