Electronic band structure of far-infrared Ga_1-xIn_xSb/InAs superlattices

Results of tight-binding and eight-band k.p calculations of the electronic band structure of long wavelength Ga_1-xIn_xSb/InAs superlattices are compared with experimental energy gap and absorption coefficient data. The effective masses, band splittings and absorption coefficients observed in this system illustrate the potential of these structures for application in focal plane array systems demanding high detectivities or relaxed cooling requirements. Comparisons with Hg_1-xCd_xTe, the industry standard, are particularly favourable at longer wavelengths (8-12 mu m and beyond), due to both a substantial reduction in tunnel currents and a suppression of impact ionization noise processes. The authors also find that the InSb- or Ga_1-xIn_xAs-like nature of the interfaces should affect the energy gap of a Ga_1-xIn_xSb/InAs superlattice, and that substantially larger optical absorption coefficients are to be expected in structures with InSb-like interfaces. Their calculations are in agreement with experimental absorption spectra and with observed dependences of energy gaps on interfacial chemistry, measured in samples in which the nature of the interfaces was controlled through appropriate shuttering sequences and use of interrupts during growth by molecular beam epitaxy.