Significantly extended cutoff wavelength of very long-wave infrared detectors based on InAs/GaSb/InSb/GaSb superlattices

Abstract

The authors report significant tunability of the bandgap in very long-wave infrared (VLWIR) InAs/GaSb/InSb/GaSb superlattices. Calculations using the empirical tight binding method have shown the flexibility in tuning the energy levels of the valence band by inserting a thin InSb layer in the middle of the GaSb layer of a normal type-II binary InAs/GaSb superlattice. Through the experimental realization of several barrier structure photodiodes with 15 ML InAs/7 ML GaSb active region, the cutoff wavelength was extended from 14.5 μm to 18.2 μm by inserting 0.6 ML InSb at different locations in GaSb layer. The agreement between the theoretical predictions and the experimental measurement suggests a way to exploit this advantage for the realization of very long-wave infrared detection without increasing the thickness of InAs layer. At 77 K, the quantum efficiency of a very long-wave detector with the cutoff wavelength of 16.9 μm reached at a maximum value of 30%, and the R0A is kept at a stable value of 10 Ω cm2 with the peak detectivity of 2.73 × 1011 cm Hz1/2/W. The operability and the uniformity in responsivity of the 320 × 256 very long-wave focal plane arrays were 88% and 80%. The noise equivalent temperature difference at 65 K presents a peak at 25 mK, corresponding to an average value of 60 mK, with an integration time of 0.5 ms, a 300 K background, and f/2 optics.