INTERBAND OPTICAL-ABSORPTION IN STRAINED INAS INXGA1-XSB TYPE-II SUPERLATTICES/

A detailed theoretical study of interband optical transitions in InAs/ InxGa1-xSb superlattices (SL's), assumed to be grown on [100] GaSb sub strates, is presented. The SL band structure is calculated from a seco nd-order 8x8 k . p model that includes strain to first order in k, as well as strain-induced corrections to the spin-orbit interaction. The eigenvalues and eigenfunctions of the SL are evaluated exactly by diag onalizing the SL Hamiltonian within a scheme that does not require tre ating the second-order k . p terms perturbatively, and does not give s purious eigenvalues;and eigenvectors. The bulk anisotropies in the ban d structure, critical in calculating the momentum matrix elements, are fully represented in the SL Hamiltonian. Additional bulk anisotropies arising from the k dependence of the strain are included. The strong anisotropies in the SL momentum matrix element and band structure dict ate that the interband linear optical-absorption coefficient cannot be reasonably approximated by simply employing zone-center matrix elemen ts to evaluate the absorption integral. For a strongly type-II SL, thi s approach would yield spurious peaks in the spectra. A more fundament al numerical approach is, therefore, essential and, to this end, the L ehmann-Taut algorithm is employed. Detailed structures attributable to the joint density of states are revealed in the calculated spectra.