Tunable photoluminescence of uniformly doped short-period GaAs doping superlattices

Uniformly doped n-p GaAs doping superlattices with smaller period lengths than have been previously considered are characterized by electrochemical capacitance-voltage profiling and low-temperature photoluminescence. In spite of the short period lengths, the n-p structures exhibit obvious doping superlattice attributes. We directly observe free-carrier confinement due to the space-charge potential in superlattices with periods as short as 12 nm. The variation of the photoluminescence energy with excitation intensity decreases with reduced period lengths, while the photoluminescence intensity increases with decreasing periodicity. We observe anomalously red-shifted emission at low photoexcitation intensity in superlattices with periods of 20 nm and less. We argue that radiative recombination between spatially arranged donor and acceptor states associated to the random fluctuations in the superlattice potential occurs in superlattices with periods less than 20 nm. The occupied impurity states give rise to screening of an effective superlattice potential and the observed photoluminescence tunability.