Publications

The effect of radiation on Hg(1-x)Cd(x)Te photodiodes is an important parameter to understand when determining the long-term performance limitations for the Cross-track Infrared Sounder (CrIS), a Fourier Transform interferometric sensor that will fly as part of the National Polar-orbiting Operational Enviornmental Satellite System (NPOESS). The CrIS sensor uses relatively large area photovoltaic detectors, 1mm in diameter. Each p-on-n Hg(1-x)Cd(x)Te photodiode consists of MBE grown, n-type material on lattice matched CdZnTe, with arsenic implantation used to form the junction. A 1mm diameter detector is achieved by using a lateral collection. Solar, and trapped protons are a significant source of radiation in the NPOESS 833 km orbits. We irradiated 22 LWIR detectors with protons at the Harvard Cyclotron Laboratory (HCL) and monitored the I-V performance and dynamic impedance of each detector. Three groups of detectors were irradiated with either 44, 99, 153-MeV protons, each between 1x10(10) - 4x10(12) p+/cm(2) (total range ~ 0.7 - 690 krad(Si)). Several I-V data sets were collected within that fluence range at all three energies. All the detectors were warmed to room temperature for approximately 96 hours following the largest proton dose, recooled, and then re-characterized in terms of I-V performance and dynamic impedance. The total noise increase predicted for CrIS after 7-years in orbit is less than 1%.