Fundamental doping limits in wide gap II-VI compounds

We review recent approaches to explain doping limitations in wide gap II-VI compounds. While fully theoretical approaches are only partly in agreement with experiments, we show that a phenomenological treatment is able to describe a large number of available data for the maximum p- and n-dopability of many different II-VI compounds with different dopants. The key parameter for the dopability in this approach is the energetic position of the band edges with respect to an absolute reference level. At a given lattice constant, this parameter can be effectively influenced by using superlattices whose band edges can be changed by the choice of the superlattice period. We give examples of proposed device designs based on this approach, where the p- and n-cladding layers are different materials with the same energy gap, but different band edge positions. For a model device we demonstrate that such asymmetric device designs can bring significant advantages.