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Published September 29, 2004 | Published
Book Section - Chapter Open

VIRGO-2K 2.25-μm HgCdTe dark current


Careful measurements for an engineering grade 2K^2 2.5μm cut-off VIRGO detector in a sealed, cold enclosure have yielded dark current twenty five times less than previously reported for these devices, putting Raytheon detectors in contention for low background applications. Global reset followed by Sample Up the Ramp readout was used to allow zero point drifts at the exposure start to be separated from true dark current and mux glow. In a sub-array selected to be far from two photo-emitting defects, mean dark current stabilized 10 hours after power-on, at 0.025 e-/s/pix at 79K (-0.1K, +0.8K). Dark current showed no evidence of the onset of a floor in the 79-104K range, but the temperature dependence was softer than expected, implying a band gap that is 20% below nominal. Shot noise from the dark current will not dominate the 18 e- read noise, unless a substantial noise reduction is achieved through multiple sampling. Hundreds of non-destructive samples will be possible without impact from multiplexor glow, which contributes only 0.04e-/pix/read for a 6μs pixel. Reset Anomaly is dependent on exposure time, settling to -60e- for long exposures, and dominating dark current in exposures less than 2400s. Reference pixels do compensate for these effects, but imperfectly, requiring further study. Attempts to explain Reset Anomaly in terms of self heating were inconclusive.

Additional Information

© 2004 Society of Photo-Optical Instrumentation Engineers (SPIE). Some of the infrastructure for these tests was funded by the California Association for Research in Astronomy in preparation for a comparison of Raytheon and Rockwell detectors for a proposed Keck IR Multi-Object Spectrometer. Continued funding for these tests was provided by the SuperNova/Acceleration Probe (SNAP) project at Lawrence Berkeley National Laboratories. At Caltech Optical Observatories, we thank Khanh Bui for mechanical design of the detector mount and enclosure and Ernest Croner for electronic fabrication. This program has benefited greatly from the ArcView data acquisition software, which was developed in collaboration with the Southern Observatory for Astronomical Research and Cerro Tololo Inter-American Observatory, a division of the National Optical Astronomy Observatories.

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