The InAsSb/GaSb superlattice structures were sandwiched by the n-InAs or p-GaSb inner and outer bulk layers. The effects of the thickness and doping concentration of inner and outer bulk layers on the interband and intersubband transitions have been studied in detail in this study. The absorption energies for InAsSb/GaSb type II superlattices were characterized by Fourier transform infrared (FTIR) spectroscopy. It was found that the intersubband transition hh1-1h1 (first heavy hole to first light hole subband) transition disappeared when the inner bulk layer thickness was smaller than 0.6 mum or the outer bulk layer thinner than 0.15 mum. The C1-hh1 (first conduction subband to first heavy hole subband) interband transitions of the p-type GaSb sandwiched superlattices were also obtained and characterized in this work. When the superlattices were sandwiched by p(+)-GaSb bulk layers, a stronger C1-hh1 absorption peak (lambda = 4 mum) was observed obviously. However, the above phenomena were vanished as the superlattices sandwiched by intrinsic GaSb bulk layers. The different long wavelengths of transitions in superlattices can be obtained by utilizing the different type of doping and concentrations of the bulk layers. (C) 2002 Elsevier Science B.V. All rights reserved.