Recombination of drifting holes with trapped electrons in stabilized a-Se photoconductors: Langevin recombination

Stabilized amorphous selenium $\mathrm{(a-}\mathrm{Se})$ is one of the x-ray photoconductors that is currently used in recently developed direct conversion flat panel x-ray image detectors. We have studied the recombination of free holes with trapped electrons in stabilized $\mathrm{a-}\mathrm{Se}.$ Electrons were deeply trapped in $\mathrm{a-}\mathrm{Se}$ by carrying out repetitive electron time-of-flight (TOF) transient photoconductivity experiments. By using conventional and interrupted field hole time-of-flight (IFTOF) transient photoconductivity techniques in a TOF, IFTOF, TOF sequence, we were able to develop a technique that allows the measurement of the capture coefficient between free holes and trapped electrons. We find that the capture process of holes by trapped electrons closely follows the Langevin recombination mechanism.