Altarelli M.
A new method for the calculation of the electronic structure of semiconductor superlattices in the envelope-function approximation is presented. The method is particularly suited to a description of type-II superlattices (e.g. InAs-GaSb). The band-edges of the constituent materials are realistically described, and appropriate boundary conditions are derived from the envelope functions. To determine the energy levels, a variational principle is obtained, which automatically produces correctly matched solutions and reduces the numerical work to a standard matrix diagonalization. Results are presented for InAs-GaSb superlattices. They reveal novel aspects of the band-crossing transition which occurs with increasing superlattice period and which produces a zero-gap or very-narrow-gap semiconductor state, rather than a true semimetal.
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