Photoluminescence and infrared spectroscopy of acceptors in GaAs

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Abstract
Time-resolved and continuous wave (cw) photoluminescence studies and infrared absorption spectroscopy have been carried out on bulk liquid-encapsulated Czochralski crystals of GaAs grown from Ga-rich and stoichiometric melts. These samples all exhibited the 78-meV residual acceptor which has been attributed previously to the neutral state of the GaAs antisite double-acceptor defect. The temperature dependence and time-resolved studies of the ∼1.44-eV photoluminescence band associated with the 78-meV residual acceptor in these samples demonstrates conclusively that the luminescence bands reported by various workers in the 1.441–1.443 eV range are all attributable to a donor-acceptor pair transition involving the same acceptor level. Two distinctly different photoluminescence bands at 1.283 eV (236-meV level) and 1.316 eV (203-meV level) can be distinguished on the basis of peak energies, temperature dependence, and time decay characteristics. The difference between these two bands was not recognized previously and both have been attributed by independent workers to the negative charge state of the GaAs antisite defect. While the quantitative correlation of the relative intensities of the ∼1.44- and 1.283-eV photoluminescence bands from sample to sample and as a function of exciting light intensity implies some relationship between these two bands, far-infrared intracenter absorption measurements indicate that this relationship cannot be as simple as that between the neutral and negative charge states of a double acceptor. However, infrared spectroscopy of the sample which exhibits the strongest 1.316-eV luminescence spectrum revealed a shallow acceptor with 203-meV binding energy and with D and C absorption line separation characteristic of a hole bound to a negatively charged (double) acceptor. This fact and a measured decay rate for the 1.316-eV luminescence band which is ∼10 times slower than that of the ∼1.44-eV band are consistent with the suggestion that the 203-meV level is the negative charge state of a 78-meV double acceptor.