Donor-acceptor recombination in short-period silicon-doped GaAs/AlAs superlattices

A low-frequency band is observed along with an exciton band in photoluminescence spectra of short-period GaAs/AlAs superlattices doped with Si in the barriers or in the barriers and wells. This band is ascribed to donor-acceptor recombination on the basis of the dependence of its frequency on the excitation intensity under cw excitation and on the time delay under pulsed excitation. Mainly type-II superlattices are investigated. The estimate EA+ED≈120 meV can be obtained from the peak energy of the donor-acceptor band with a very weak excitation intensity. The estimates EA≈23 meV and ED≈90 meV are obtained from the temperature dependence of the band intensity. It is suggested that the deep donor level is associated with a DX center in the AlAs layers.