Generation-Recombination Effect in MWIR HgCdTe Barrier Detectors for High-Temperature Operation

An advanced numerical model was applied to investigate dark current-voltage characteristics of high operating temperature (HOT) HgCdTe p⁺BpnN⁺ and p⁺BppN⁺ barrier detectors operated in midwave infrared spectral range. In addition to diffusion mechanisms, all assumed generation-recombination effects, including Shockley-Read- Hall (SRH) mechanism associated with metal site vacancies and dislocations, tunneling, and impact ionization, allow more precise interpretation of obtained experimental results. Investigated structures have the same cap-barrier structural unit (pBp) and N⁺ bottom contact layer but a different nand p-type absorption layer optimized at cutoff wavelength up to 3.6 μm at 230 K. Both type barrier detectors exhibit very low experimental dark currents, in the range of 2-3 × 10^-4 A/cm² at 230 K. Calculations show that currents in the device with the n-type absorber are limited by Auger processes while currents in the device with the p-type absorption layer are mainly associated with SRH mechanisms. A reduction of the thermal generation rate in a wide bandgap barrier is observed. The presence of the enhanced electric field in the depletion regions increases trap-assisted tunneling via traps located at dislocation cores. In high-quality materials, with a reduced number of structural defects, the device with p-type absorption layer should provide lower dark currents in HOTs.