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

摘要

An advanced numerical model was applied to investigate dark current–voltage characteristics of high operating temperature (HOT) HgCdTe pBnN and pBpN 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 (pB) and N bottom contact layer but a different n- and p-type absorption layer optimized at cutoff wavelength up to at 230 K. Both type barrier detectors exhibit very low experimental dark currents, in the range of 2– A/cm 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.