Table 2.

Effects of charge carrier trapping in the x-ray photoconductor layer (e.g., a-Se) on various image sensor metrics. We assume that the radiation receiving electrode is positively biased and the negative electrode is pixellated. Reversal of the biasing potential results in identical effects for the opposite charge.

Phenomenon	Primary observable effects	Comment	Example reference
Hole or electron trapping. The capture of carriers into deep traps.	Reduction in sensitivity Reduction in DQE(0) Reduction in MTF for hole trapping Increase in MTF at high spatial frequencies for electron trapping	Radiation receiving electrode is positive	[82,86–88, 90,91]
Hole recombination with previously trapped electrons	Reduction in sensitivity Ghosting	Similar effects if electrons recombine with previously trapped holes	[81]
Bulk electron and hole recombination	Reduction in sensitivity Loss of linearity in collected charge vs. exposure	At very high doses that lead to large concentrations of drifting electrons and holes in the bulk.	[95]