Direct probing of type-II band configurations in semiconductor superlattices

We propose a novel technique to test directly and unambiguously the occurrence of type-II energy-band configurations in semiconductor superlattices. We insert a perturbation in the sublayers of larger band gap, using a localized isoelectronic substitution of the material. The resulting shifts of the superlattice's optical transitions probe the localization of the electrons or the holes in the perturbed sublayer. This technique has been applied to GaAs/AlAs indirect structures, and to the controversial Inₓ{Ga}_{1{{-}}x}$As/GaAs system.