Comprehensive analysis of epitaxial Al/Al_xGa_1-xAs Schottky barriers made by MBE: Barrier heights and band edge discontinuities

Extremely high quality epitaxial aluminium on Al_xGa_1-xAs Schottky diodes have been prepared by MBE. The excellent electrical properties of the MBE grown AlGaAs layers, with residual deep-level concentrations of less than 10¹⁴cm^-3, combined with the in-situ deposition of single crystal epitaxial aluminium resulted in Schottky diodes with accurately exponential current-voltage characteristics over up to 6 decades of current and with ideality factors, for all but one of the diodes, less than 1.04 for x from 0 (GaAs) to 1 (AlAs). The dependence of the Schottky barrier heights on the aluminium mole fraction was determined using I V and C/V measurements. A comparison of the data from n- and p-type diodes shows the pinning level responsible for the barrier height to be the same in both cases; the sum of the barrier heights giving a bandgap dependence on composition consistent with other data. The compositional trends of the barrier heights are shown to be in close agreement with accepted GaAs/AlGaAs conduction and valence band offsets, supporting the idea of a relationship between Schottky barriers and heterojunction band offsets.