Space-Charge-Limited Photocurrents and Transient Currents in (Cd,Zn)Te Radiation Detectors

We combine steady-state photoconductivity and laser-induced transient current measurements under above-band-gap illumination to study space-charge formation in ($\mathrm{Cd},\mathrm{Zn})\mathrm{Te}$. Analytical and numerical models describing space-charge-limited photocurrents are developed and excellent agreement with measured data is obtained, especially with the Drift-diffusion model. A linear rise of photocurrent at low voltage is observed and ascribed to the trapping of injected holes in the region close to the cathode side. The influence of space-charge formation, the influence of photoconductive gain, and the contribution of shallow and deep levels to photocurrent-voltage characteristics are numerically simulated. According to measurements and calculations, recent principles used to evaluate detector properties, mainly the mobility-lifetime product, via the photoconductivity are critically assessed.