Effects of passivation and extraction surface trap density on the 1/f noise of HgCdTe photoconductive detector

Experimental results are presented for noise voltage, responsivity, and specific detectivity (D*) for the long wavelength infrared (IR) HgCdTe photoconductive detectors. Hg/sub 0.8/Cd/sub 0.2/Te photoconductive detectors passivated with ZnS/photo-enhanced native oxide have an improved noise spectral density and D* than the detectors passivated with only ZnS. The low frequency 1/f noise charges were measured for a Hg/sub 0.8/Cd/sub 0.2/Te photo detector, as a function of bias at 77 K, and the effective surface trap density determined from the 1/f noise charges measured at 1 Hz. It was found that the surface effective trap densities of stacked passivated sample and the sample passivated only with ZnS are close to 4×10/sup 17/ and 9×10/sup 17/ cm/sup -2/ eV/sup -1/ under 0.4 V bias and 1 μs integration time, respectively. We found that the numerical values of noise are strongly dependent upon surface passivation properties. It can be seen clearly that an HgCdTe photo detector with a stacked ZnS/photo-enhanced native oxide passivation is better than the HgCdTe photo detector passivated with a single ZnS layer.