Suppression of Tunneling Dark Current Through M-Region Tuning in InAs/GaSb VLWIR Photodetectors

As the cutoff wavelength of InAs/GaSb type-II superlattice infrared photodetectors is extended from mid-wavelength to very long-wavelength, the bandgap in the absorber layer exhibits a progressive narrowing. In the case of infrared photodetectors with PIMN structures, this phenomenon results in a rapid increase in the tunneling dark current between the I and M regions. In this paper, we present a very long-wavelength InAs/GaSb infrared photodetector with a PIMN structure, in which the depletion region is shifted from between the I- and M-regions to between the M- and N-regions. This was achieved by modifying the doping type of the M-region to a slight p-type and reducing the thickness of the M-region. This resulted in the effective suppression of the tunneling dark current. Following theoretical and experimental optimization, the device exhibited a quantum efficiency exceeding 31% at 77 K for an M-region thickness of 166 nm and a cutoff wavelength of more than 14 μm. The activation energy, Ea, increases from 31 meV to 42 meV (half the bandgap) when the device is between 90 K and 150 K, indicating that the dominant dark current of the device changes from tunneling dark current to Generation-recombination dark current. Following optimization, the RA<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bulk</sub> of the device increased by over 60 times, reaching a value of 182 Ω-cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, while the tunneling dark current was significantly suppressed.