Intersubband absorption in Ga1 - xAlxSb/AlSb superlattices for infrared detection

The infrared absorption from intersubband transitions between the lowest two superlattice conduction minibands is investigated for n-type Ga_1-xAl_xSb/AlSb superlattices. In such an indirect semiconductor superlattice, intersubband transitions can be induced by normally incident light because of the effective-mass anisotropy and the tilted orientation of conduction-band valleys with respect to the growth direction. The absorption coefficients and peak transition wavelengths are calculated for superlattices grown in the [001], [110], and [111] directions for both normal and parallel incidence. In the [110] Ga_1-xAl_xSb/AlSb superlattice, peak absorption coefficients of 5000-7000 cm^-1 are obtained for both normally and parallel incident radiation in the wavelength range of 8-14 μm with moderate sheet doping concentrations of 10¹² cm^-2. The ability to detect normally incident radiation and to achieve absorption comparable to that in the GaAs/Ga_1-xAl_xAs detectors makes the Ga_1-xAl_xSb/AlSb devices promising for future applications in long-wavelength infrared detection.