Fermi level pinning in low‐temperature molecular beam epitaxial GaAs

The Fermi level position in low temperature (LT) GaAs has been studied by photoreflectance (PR). By etching the LT‐GaAs to a different thickness, we find the Fermi level in the as‐grown as well as the annealed LT‐GaAs is firmly pinned. The pinning position, however, occurs at different energies: 0.47 eV below the conduction band edge for the as‐grown samples and 0.65 eV below the conduction band edge for the annealed samples. The pinning in the as‐grown LT‐GaAs is believed to be the result of a high degree of charge compensation by deep levels, while the pinning in the annealed LT‐GaAs is due to the depletion of carriers by the Schottky barrier at the metallic As precipitates. From the measured Fermi level and ionization ratio of As antisites, the (0/+) donor level of the As antisite in LT‐GaAs is, for the first time, determined at Ec−0.57 eV.