A novel secular equation for the coupled-band envelope-function approximation for superlattices and application to InAs/InxGa1-xSb superlattices

This paper derives and demonstrates a new secular equation for the coupled-band envelope-function approximation (EFA) formalism for superlattices in order to overcome the difficulty of handling rapidly growing or decaying wavefunction components, in particular, the 'wing solutions'. In a second development, the generally nonHermitian secular equation is made Hermitian, making it easier to locate multiply degenerate roots. In the process, the simple Kronig-Penney model is recast into a form closely related to that for the underlying quantum well (QW) problem. The present method is applicable to Burt's EFA formalism. An InAs/InGaSb type-II superlattice is used to demonstrate the method. (C) 1997 Academic Press Limited.