Effect of contact doping in superlattice-based minority carrier unipolar detectors

We report the influence of the contact doping profile on the performance of superlattice-based minority carrier unipolar devices for mid-wave infrared detection. Unlike in a photodiode, the space charge in the p-contact of a pMp unipolar device is formed with accumulated mobile carriers, resulting in higher dark current in the device with highly doped p-contact. By reducing the doping concentration in the contact layer, the dark current is decreased by one order of magnitude. At 150 K, 4.9 μm cut-off devices exhibit a dark current of 2 × 10^-5A/cm² and a quantum efficiency of 44%. The resulting specific detectivity is 6.2 × 10¹¹ cm Hz ^1/2/W at 150 K and exceeds 1.9 × 10¹⁴ cm Hz ^1/2/W at 77 K.