Very high quantum efficiency in InAs/GaSb superlattice for very long wavelength detection with cutoff of 21 μm

The authors report the dependence of the quantum efficiency on beryllium concentration in the active region of type-II InAs/GaSb superlattice infrared detector with a cutoff wavelength around 21 μm. It is found that the quantum efficiency and responsivity show a clear delineation in comparison to the doping concentration. The quantum efficiency is further improved by gradually doping in the absorbing region. At 77 K, the 50% cutoff wavelength of the VLWIR detector is 18 μm, and the R0A is kept at a stable value of 6 Ω cm2. Different beryllium concentration leads to an increase of an average quantum efficiency in the 8–15 μm window from 35% to 55% with a π-region thickness of 3.0 μm, for Ubias = −0.3 V, and no anti-reflection coating. As for a further result, the quantum efficiency reaches at a maximum value of 66% by gradually doping in the absorbing region with the peak detectivity of 3.33 × 1010 cm Hz1/2/W at 15 μm.