InAs/InGaSb superlattices for very long wavelength infrared detection

New infrared detector materials with high sensitivity, multi-spectral capability, improved uniformity and lower manufacturing costs are required for numerous long and very long wavelength infrared imaging applications. One materials system has shown great theoretical and, more recently. experimental promise for these applications: InAs/InxGa1-xSb type-II superlattices. In the past few years, excellent results have been obtained on photoconductive and photodiode samples designed for infrared detection beyond 10 microns. Far-infrared photoresponse of superlattices with cut-off wavelengths between 15 mum and 25 mum were studied. The measured photoresponse spectra for both photodiodes and photoconductors are compared to calculated absorption coefficient spectra. The electronic structure and the optical absorption of InAs/ InxGa1-xSb superlattice infrared (IR) detector structures are calculated, for several values of x, using our implementation of the 8x8 envelope-function approximation (EFA) formalism. Good experimental-theoretical agreement is obtained regarding the long-wavelength threshold and absorption shape.