Luminescent Properties of Energy-Band-Tail States in GaAs:Si

Several new properties which are characteristic of energy-band-tail states have been measured by transient photoluminescence in samples of GaAs heavily doped with silicon and partially compensated. Their dependence on temperature, doping and excitation intensity, and geometry has been determined. The primary results are the wide range ({~} 100:1) of luminescent rise and decay times within the single emission band found at low temperatures, these times increasing monotonically with decreasing energy. These results are ascribed to the localized nature of band-tail states and to the necessary spatial separation of states in the tails of the valence and conduction bands. These observations also lead to the conclusion that thermalization times of the deeper band tails are very long --- exceeding the carrier lifetimes, which reach several microseconds in some cases. Therefore, quasiequilibrium conditions do not develop in any of these experiments.