Hg diffused Hg1-xCdxTe photodiodes for LWIR direct detection applications

Current voltage data between 70K and 160K were modeled as a summation of diffusion and space charge generation-recombination (G-R) currents. The G-R current had the correct temperature dependence, described quantitatively as surface G-R with WoSo=177cm²/sec. The diffusion current was unambiguously determined, had the correct temperature dependence, and fit quantitatively with measured material parameters: Le=15µm and NA=6.4×10¹⁶/cm³. Capacitance-voltage at 1MHz showed the diodes were essentially n-i-p structures. Photoresponse from 70K to 160K at both zero bias and large reverse bias show that quantum efficiency above 70%, the classical wavelength dependence, and cutoff wavelength which shortens at higher temperature. Heterodyne sensitivity measurements to a factor of 4.5 of the quantum noise limit were made at 77K to 110K for bandwidths of 1.5GHz. This bandwidth decreases at higher temperature due to increase in the intrinsic carrier concentration, giving increased detector capacitance and thus a larger RC time constant.