The photoluminescence from p-type Al0.67Ga0.33As epitaxial layers that had been grown by using metalorganic vapor-phase epitaxial techniques, and doped with residual C, were studied at 10K. The photoluminescence spectra exhibited 2 distinct ranges. One of these was dominated by photoluminescence lines which were related to X-band shallow impurities (acceptor C and a background donor which was predominantly Si). The other included a structural broad band which began at some 0.3eV below the band gap. The ionization energies for the C and Si were deduced to be about 0.039 and 0.052eV, respectively. The broad band consisted of 4 poorly resolved peaks at 1.8, 1.74, 1.67 and 1.6eV; with a half-width of more than 0.05eV. Their photoluminescence intensities exhibited a very specific temperature dependence, with a maximum at temperatures where the persistent photoconductivity that had been reported for n-type material was quenched. Experiments which used selective above-bandgap excitation revealed the existence of a threshold for the broad band excitation. The excitation density dependence of the broad band exhibited some super-linearity for excitation densities of more than 1.5W/cm2. These properties of the broad band suggested that it was related to non-equilibrium DX- centers, which perhaps resulted in a 2-step optical recharging process of the form: D+ + e-  D0 and D0 + e*  DX-, where the e* were so-called hot electrons. Two models were developed in order to account for the broad band. One of them assumed the occurrence of radiative transitions (h, DX-), while the other considered internal radiative transitions from the DX0 state, of the distorted configuration, to the DX- state.

P.Gladkov, K.Zdánský: Journal of Applied Physics, 1996, 80[5], 3004-10