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 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-mu-m with moderate sheet doping concentrations of 10(12) 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.