Fermi level of low-temperature-grown GaAs on Si-δ-doped GaAs

We have studied the Fermi level of low-temperature-grown GaAs on the top of Si-δ-doped GaAs by photoreflectance. The Fermi levels of the as-grown and annealed samples are measured by a method which involves the photovoltaic effect and the Fermi-level pinning. Our measurements determine the position of the Fermi-level pinning, and the results have been discussed in connection with the defect model and the buried-Schottky-barrier model.