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Near band-gap photoluminescence of the MOCVD-grown heavily Si-doped GaAs

The luminescence of Si-doped GaAs with electron concentration up to 2.1*1019 cm-3 is investigated. For the epitaxial layers with electron concentration less than 1*1018 cm-3 the donor-acceptor pair luminescence was found to dominate, while at greater concentrations the indirect free electron transitions to the shallow acceptors prevail. The dependence of the luminescence spectra on the doping level was found to be different for two groups of layers. For the first group the spectra shifted to higher energies with increasing electron concentration in agreement with calculations of the Moss-Burstein effect, while for the second group there was almost no shift of the spectra up to n=2.1*1019 cm-3. The measurements of luminescence excitation spectra have shown that the Fermi level is stabilised for the latter group of layers some 40-60 meV above the bottom of the conduction band. The presence of resonant levels in the conduction band of GaAs:Si was included to explain the Fermi-level stabilisation.