Abstract
We report a study of a defect responsible for the "g" bound exciton line at 1.511 2 eV that is frequently detected in photoluminescence spectra of GaAs grown by molecular beam epitaxy (MBE). A direct correlation has been observed between this line and a transition at 1.494 6 eV, which is shown to result from a conduction band-to-acceptor recombination involving a shallow, unidentified acceptorlike defect that is labeled "A." The activation energy of the defect is 24.8±0.2 meV, about 1.7 meV lower than that of C As acceptor. Upon hydrogenation the defect is passivated more extensively than any known shallow acceptor species in GaAs. This result is analyzed in terms of a passivation model, from which it can be inferred that the A defect is not due to a simple substitutional Group II impurity on a Ga site. Incorporation of the A defect strongly affects the luminescence properties of the material. An almost complete quenching of the donor-bound exciton lines, profound changes in the line shape and relative intensity of the free exciton recombination, and appearance of a sharp transition of unknown origin at 1.513 8 eV were observed with increasing defect concentration. Apparently "donorless" low temperature exciton recombination spectra are reported for defect-rich p-type MBE GaAs layers with donor concentrations as high as 7×10 14 cm -3 and compensation ratios of ∼0.3. The dependence of the defect incorporation on MBE growth parameters is discussed. The feasibility of MBE growth of high purity, nearly shallow defect-free p-type GaAs layers at marginally As-stabilized surface conditions over an about 1-5 μm/h range of deposition rates is demonstrated.