Monte Carlo Simulation of Time of Flight Transient Photocurrents in High Resistivity Semiconductors with Shallow and Deep Traps: Effects of Photoinjection Strength, Duration and Absorption Depth

Amorphous selenium (a-Se) alloys are currently used as x-ray photoconductors in modern digital direct conversion flat panel detectors. Time-of-flight (TOF) transient photoconductivity technique is widely used in the characterization of a-Se alloy photoconductors for quality control. Using MATLab as a modeling tool, Monte Carlo techniques have been performed to simulate the transport of photogenerated charge carriers through a readily definable generic photoconductor material. High carrier injection ratios, finite absorption depths, as well as long photogeneration times are examined to evaluate their effects on the propagating charge carrier packet and transient photocurrent shape. It is assumed that the photoconductor has a set of shallow traps and a set of deep traps. The distinct effects of shallow and deep trapping on the transient photocurrent are also examined subject to different levels of photoinjection. The extent of carrier charge dispersion during drift is also examined as a function of the injection ratio, photogeneration absorption and duration, and the capture and release times associated with localized sates