Abstract
We report measurements of low-temperature luminescence spectra, lifetime, and excitation spectra for excitons in (, where is the direct-to-indirect crossover value) over a wide range of excitation levels. The no-phonon line, ∼6 meV wide, decays nonexponentially at low excitation levels. The decay rate depends strongly on excitation intensity and on temperature (for K) while the position and width remain unchanged. We show that in the low-temperature, low-excitation limit, the nonexponential decay, and its dependence on , can be quantitatively explained in terms of emission from a small number of localized indirect excitons scattered by alloy fluctuations. Above 8 K these excitons become mobile and their decay is exponential. Most of the excitons are mobile even at 2 K. They dominate the emission when the excitation is sufficiently strong to neutralize the ionized impurities, which quench the luminescence at low intensities. The localized excitons show strong LO-phonon sidebands, while the mobile ones do not. The theory of the decay rate yields a mean value of the scattering strength eV, in reasonable agreement with estimates from the Al-Ga electronegativity difference. The nitrogen-bound exciton with a wide range of binding energies, previously reported in ion-implanted samples, is found to be split, possibly by a disorder-induced axial field.
- Received 30 July 1982
DOI:https://doi.org/10.1103/PhysRevB.27.2362
©1983 American Physical Society