Surface structures and photoluminescence of molecular beam epitaxial films of GaAs

Abstract

Surface structures were observed during molecular beam epitaxial growth of GaAs in situ in an ultrahigh vacuum high energy electron diffraction (HEED) system. The surface structures were related to the relative populations of gallium and arsenic on the substrate surface when the intensities of gallium and arsenic in the molecular beam were varied during growth. On the GaAs ( 111) face a ( 111)-2 surface structure is interpreted in terms of an arsenic-rich surface condition and a ( 111)-√ 19 structure is interpreted in terms of a gallium-rich condition. Only the (111)-2 surface structure was observed on the (111) face. The presence of these different surface structures under different growth conditions is interpreted in terms of rearrangements of the unshared bonds of the atoms on the crystal surface. Photoluminescence measurements were used to investigate the radiative recombination characteristics of the films grown with either a ( 111)-2 or a ( 111)-√ 19 structure present on the surface. The results show that the near gap photoluminescence intensity from a film grown under the latter condition is much higher than that from the former. A broad photoluminescence peak ∼ 0.1 eV below the band gap energy is observed on all epitaxial layers grown with the ( 111)-2 structure present on the surface. The peak may be reduced by annealing and may be attributed to centers associated with Ga vacancies.