Abstract
The absorption energies for InAsSb/GaSb type II superlattices were characterized by Fourier Transform Infrared (FTIR) spectroscopy. The InAsSb/GaSb superlattice structures were sandwiched by 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. If the modulated Fermi-level was located at an inappropriate position, the FTIR absorption peaks will shift and destroy. It was found that the intersubband transition hhl-lhl (first heavy hole to first light hole subband) disappeared when the inner bulk layer thickness was smaller than 0.6 µm or the outer bulk layer thinner than 0.15 µm. When the Fermi-level was modulated to lie between hhl and 1hl by changing the doping concentration of silane in bulk layers, the intensity of hhl-lh intersubband transition (λ=14 µm) increased to be much stronger than the Cl-hhl (first conduction subband to first heavy hole subband) transition (λ=3.8 µm). The superlattices sandwiched by p-type GaSb were also formed to study the Cl-hhl interband transitions. When the superlattices were sandwiched by p+-GaSb bulk layers, a stronger Cl-hhl absorption peak (λ=4 µm) was observed. But it disappeared when the superlattices were sandwiched by intrinsic GaSb bulk layers, because the Fermi-level of intrinsic GaSb rose above the Cl subband. So, 3-5 or 8-12 µm different wavelengths can be obtained by utilizing the different dopant-type and controlling the doping concentration of the bulk layers.
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