Theoretical investigation of InAs/GaInSb type-II superlattice infrared detectors for long wavelength and very long wavelength infrared applications

Abstract

Type-II superlattices (SLs) based on InAs/GaInSb material systems have been theoretically investigated and optimized to achieve large valence band splitting and thin constituent layers, which are desirable for high detectivity and large absorption coefficient for the long-wavelength infrared (LWIR) and very long-wavelength infrared (VLWIR) detection covering the waveband from 8 to 14 μm and longer. Two approaches have been employed to optimize the SL: the first approach is to increase the InSb mole fraction in GaInSb alloy, keeping the balance between the compression and tension in the SL, and the second approach is to increase the SL thickness ratio, allowing small misfit in the SL. In the first approach, the valence band splitting was found to increase with increasing InSb composition and reached a maximum at 25% of InSb composition for 9 μm and at 30% of InSb composition for 11, 13, 15, 17, and 19 μm peak wavelength, respectively. When the thickness ratio is increased with fixed InSb composition, the valence band splitting has its maximum around a thickness ratio of 2–3, but the advantage of increasing the thickness ratio is obtained only for SL with less than 15% of InSb composition. It was also found in the first approach that higher InSb composition in GaInSb alloy was very efficient in reducing the total thickness of one period of SL up to 35% of InSb mole fraction. In the second approach, the minimum thickness of SL is obtained at the point where the valence band splitting is maximized. However, since the second approach is useful only for InSb composition less than 15%, the reduction of total thickness of SL is less effective than the first approach. Consequently, we can design high performance type-II SL IR detectors by both approaches for LWIR and VLWIR applications.