VIRGO-2K 2.25-μm HgCdTe dark current

Abstract

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.

Files

Additional details