Optical Properties of Ordered and Randomly Disordered AlAs/GaAs Short-Period Superlattices

The optical properties of different atomic arrangements of Al0.5Ga0.5As, deposited by molecular-beam epitaxy and having nominally identical average composition, have been compared. Markedly different signatures are seen in steady-state, time-resolved, and microwave-modulated photoluminescence, photoreflectance, and photoluminescence-excitation spectroscopies for a random pseudobinary alloy and (AlAs)n(GaAs)4-n superlattices where n=2 (ordered) or n is randomly chosen (disordered) from the sets [1,2,3] or [0,1,2,3,4]. When n=[0, 1, 2, 3, or 4] the optical properties are dominated by quantum confinement effects due to the presence of layers with thicknesses up to 14 monolayers. When n=[1, 2, or 3] the optical properties are consistently described by the presence of disorder-induced localized states and a hopping-assisted recombination mechanism.