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

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Abstract
The infrared absorption from intersubband transitions between the lowest two superlattice conduction minibands is investigated for n‐type Ga1−xAlxSb/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] Ga1−xAlxSb/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/Ga1−xAlxAs detectors makes the Ga1−xAlxSb/AlSb devices promising for future applications in long‐wavelength infrared detection.