TAILORING INAS GA1-XINXSB SUPERLATTICES FOR LONG-WAVELENGTH IR APPLICATIONS/

A systematic study has been carried out on the design of long-waveleng th infrared detector materials from InAs/GaSb and InAs/GaInSb superlat tices with absorption energies below 250 meV, i.e. lambda > 5 mu m. Th e influence from layer thicknesses and alloy composition on cut-off wa velength and optical matrix element has been analysed. A three-band en velope-function model including strain effects was used to calculate c onduction-band electron and valence-band light-hole states, while an e ffective-mass approximation was used to describe heavy-hole states. In order to achieve useful absorption coefficients, the period of such s uperlattices must be less than typically 20 monolayers. Calculations r evealed that the absorption can be increased with almost unaffected cu t-off wavelength by reducing the GaInSb thickness. The effects of incl uding a small amount of In in the GaSb in order to reach longer wavele ngths were studied. One conclusion is that although it makes longer wa velengths possible, it also makes the cut-off wavelength much more sen sitive to monolayer and composition fluctuations.