Novel type II strained layer superlattices for long wavelength infrared detectors

Novel type II (InAs)Na/(InxGa1−xSb)Nb short period strained layer superlattices (SLs) have shown considerable promise as candidates for applications in infrared imaging in the 10–12 μm wavelength regions and beyond. Absorption α(ℏω) calculations are difficult, however, because of the strong misalignment of the band edges of the two host materials at the interface and because of a large lattice mismatch. Theoretical studies of the energy band gaps and cut-off wavelengths in (InAs)Na/(InxGa1−xSb)Nb SLs grown on GaSb are reported as a function of composition and layer thickness using a modified second neighbor empirical tight-binding (ETBM), effective bond-orbital (EBOM) and 8×8 k.p models. The strain in the ETBM is included by scaling the matrix elements according to the Harrisonʹs universal 1/d2 rule and by appropriately modifying the angular dependence. The EBOM and k.p calculations include the strain via the deformation theory. By appropriate choice of the In composition and layer thickness, cut-off wavelengths (λc) in the 10–12 μm range are achievable. The study of α(ℏω) for thin layer SLs in the k.p scheme suggest enhancement of absorption with increaing x at a fixed energy due to a large overlap of the electron–hole wavefunctions.