The broad-band photoluminescence spectra typical of bulk-grown or low-purity epitaxial GaAs breaks into a number of sharp emission lines in very-high-purity GaAs. At low temperatures (∼2°K), emission peaks due to free excitons (1.5156 eV), excitons bound to neutral (1.5145 eV) and ionized (1.5133 eV) donors, and excitons bound to neutral (1.5125 eV) and ionized (1.4886 eV) acceptors are identified. Also, band-acceptor (1.4926 eV) and donor-acceptor (1.4857 eV) recombination is observed. The assignments are based on dependence of the emission lines with temperature, impurity content, and carrier type ($n$- or $p$-type material), as well as on the relative energy positions. The temperature dependence of the exciton-neutral-donor complex appears to be influenced by nonradiative Auger recombination.

• Received 18 March 1968

DOI:https://doi.org/10.1103/PhysRev.176.993