Capacitance measurements of HOT LWIR Auger-suppressed HgCdTe IR detectors

This work presents the capacitance measurements of mercury cadmium telluride (HgCdTe, MCT) heterostructure-based infrared (IR) detector. The experiments were performed versus temperature (80 K to 300 K), bias (0.2 V to −1 V), and frequency (100 Hz to 5 MHz). The examined detector is prepared to operate in long-wave infrared range (LWIR, λ cut-off (50%) = 10.6 μm) and high operating temperature conditions (HOT), without cryogenic cooling. The results show that capacitance can exhibit a non-trivial effect, especially for devices designed to obtain dark-current decrease by Auger generation-recombination suppression. The results demonstrate that the capacitance manifests a strong frequency dependence and may even reach negative values under certain conditions. A distinct increase in capacitance at low frequencies (< 500 kHz), followed by a stable plateau in the MHz range, is clearly observed and can be attributed to the diffusion capacitance and trap-sourced effect. Using the obtained results, reduced doping concentration, depletion width, and trap concentration were also estimated as a practical implementation of capacitance measurements. For high-speed applications, selecting the optimum detector bias and temperature is crucial to minimize capacitance, which, as demonstrated, can vary by orders of magnitude from nF to pF. Consequently, the time constants were theoretically calculated and compared with previously reported values. The results proved the possibility of sub-ns operation in such devices when the operating conditions are properly selected.