Photoconductor selection for digital flat panel x-ray image detectors based on the dark current

We consider a flat panel direct conversion x-ray image detector in which a photoconductor is used to directly convert absorbed x-ray photons to collectable electron hole pairs. The storage capacitor at each pixel stores a quantity of charge proportional to the incident radiation. The charge stored at each pixel is read out every Δt seconds. Based on a condition for a minimal dynamic constraint, we have examined the corresponding range of constraints on the material properties to establish approximate x-ray photoconductor selection criteria. We consider requirements for radiology and fluoroscopy in which Δt=1 and 1/30 s, respectively. When the electrical contacts are totally blocking, the dark current is limited by bulk thermal generation. Minimum band gap Eg requirements depend on the concentration of defects Nd around the Fermi level and their recombination cross section Sr. For single crystal photoconductors with a neutral-defect concentration of the order of ∼1014 cm−3, we need Eg>1.5 eV for fluoroscop...