Large VLWIR Hg1−xCdxTe photovoltaic detectors

Advances in MBE growth of HgCdTe and detector architectures have resulted in high performance detectors fabricated in the 15-17 mu m spectral range. Recently, VLWIR (lambda c approx equal to 17 mu m at 78 K) photovoltaic large (1000 mu m diameter) detectors have been fabricated and measured at flux values targeting remote sensing interferometry applications. The operating temperature is near 78 K, permitting the use of passive radiators in spacecraft to cool the detectors. Detector non-AR coated quantum efficiency > 60% was measured in these large detectors. A linear response was measured, while varying the spot size incident on the 1000 mu m detectors. This excellent response uniformity, measured as a function of spot size, implies that low frequency spatial response variations are absent. The 1000 mu m diameter, lambda c approx equal to 17 mu m at 78 K detectors have dark currents approx 160 mu A at a -100 mV bias and at 78 K. Interfacing with the low (comparable to the contact and series resistance) junction impedance detectors is not feasible. Therefore a custom preamplifier was designed to interface with the large VLWIR detectors operating in reverse bias. A breadboard was fabricated incorporating the custom designed preamplifier interfacing with the 1000 mu m diameter VLWIR detectors. Response vs flux measurements were made on the large VLWIR detectors and nonlinearity < 0.15% was measured at high flux values in the 2.5 x 10 17 to 3.5 x 10 17 ph cm -2 s -1 range. This nonlinearity is an order of magnitude better than for photoconductive detectors. 14 refs.