Transient and steady-state dark current mechanisms in polycrystalline mercuric iodide X-ray imaging detectors

A theoretical model for describing bias-dependent time transient and steady-state dark current behaviors in polycrystalline mercuric iodide (poly-HgI2) based X-ray image detectors is developed. The model considers carrier injection from the metal electrode, bulk carrier depletion process, and bulk thermal generation current from the mid-gap states. The transient dark current is mainly determined by the initial carrier depletion process. At a very low applied field (less than 0.05 V/μm), the steady-state dark current is almost equal to the bulk thermal generation current. However, the injection current increases sharply with increasing the applied field. The steady-state dark current in poly-HgI2 detectors at normal operating field (~ 1 V/μm) is mainly controlled by the Schottky emission of electrons from the metal/HgI2 contact. The fitting of the physics-based model to the experimental results estimates the effective barrier height and interface defect states for injecting electrons from the metal to poly-HgI2 layer in various poly-HgI2 detectors.