1. Radiation-Induced Emission From The CdZnTe Substrate of the WFC3 IR Detectors
Bob Hill
June 23, 2005
June 23, 2005
SDW 2005, Taormina

2. Background Seen During Radiation Testing
Diffuse background detected for proton energies that significantly penetrate into the CdZnTe substrate.
Background seen even when protons do not reach HgCdTe detection layer.
Morphology of background intensity resembles short wavelength flat fields.
Background signal is, to first order, proportional to energy deposition in CdZnTe, but there is evidence for diminished effect from energy deposited farther from HgCdTe layer.
Conclusion: the background effect is produced in the CdZnTe layer (likely the production of IR photons near the CdZnTe transmission edge).
Radiation-induced background morphology
800 nm flat-field morphology
June 23, 2005
SDW 2005, Taormina

3. Insignificant Background Seen In Substrate-Removed Detector
Substrate On
Substrate Off
The diffuse radiation-induced background (between the hits) is reduced to undetectable levels when the substrate is removed.
Estimated upper limit to the on-orbit signal is 1e-4 e-/sec/pix, orders of magnitude below the detector dark current and zodiacal background.
June 23, 2005
SDW 2005, Taormina