Molecular beam epitaxy of interband cascade structures with InAs/GaSb superlattice absorbers for long-wavelength infrared detection
The interfaces of InAs/GaSb superlattices (SLs) were studied with the goal of improving interband cascade infrared photodetectors (ICIPs) designed for the long-wavelength infrared region. Two ICIP structures with different SL interfaces were grown by molecular beam epitaxy, one with a ~1.2 monolayer (ML) InSb layer inserted intentionally only at the GaSb-on-InAs interfaces and another with a ~0.6 ML InSb layer inserted at both InAs-on-GaSb and GaSb-on-InAs interfaces. The material quality of the ICIP structures was similar according to characterization by differential interference contrast microscopy, atomic force microscopy, and x-ray diffraction. The performances of the ICIP devices were not substantially different despite the different interface structure. Both ICIPs had a peak detectivity of >3.7 × 1010 Jones at 78 K with a cutoff wavelength near 9.2 μm. The maximum operation temperatures of both ICIPs were as high as ~250 K, although the structures were not fully optimized. This suggests that the two interface arrangements may have a similar effect on structural, optical and electrical properties. Alternatively, the device performance of the ICIPs may be limited by mechanisms unrelated to the interfaces. In either case, the arrangement of dividing a thick continuous InSb layer at the GaSb-on-InAs interface into thinner InSb layers at both interfaces can be used to achieve strain balance in SL detectors for longer wavelengths. This suggests that with further improvements ICIPs should be able to operate at higher temperatures at even longer wavelengths.