A gate-controlled HgCdTe long-wavelength infrared photoconductive detector

A gated photoconductor structure is proposed for the dual purpose of enhancing the performance of and investigating surface effects in HgCdTe photoconductive infrared detectors. It is verified both theoretically and experimentally that the passivating native oxide which accumulates the HgCdTe surface, thereby quenching surface recombination, also causes excessive surface shunting and an overall reduction in device responsivity. It is found that for x=0.23 Hg1-xCdxTe photoconductive detectors passivated with native oxide/ZnS the optimum surface conditions prevail at a gate bias corresponding to a semiconductor surface potential of 50 mV. Experimentally, it is found that operation at this optimum condition yields approximately a 70% increase in responsivity in comparison to floating gate conditions, which corresponds to a surface potential of 72 mV for the as-grown native oxide/HgCdTe interface. The gated photoconductor is shown to be a powerful diagnostic device structure that can be used to evaluate and optimize surface passivation layers for HgCdTe infrared detectors.