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

Abstract

We combined steady-state photoconductivity and laser-induced transient current measurements under above-band-gap illumination to study the space charge formation in CdZnTe. Analytical as well as numerical models describing space charge limited photocurrents were developed and an excellent agreement with measured data was obtained especially with the Drift-diffusion model. Linear rise of photocurrent at low bias was observed and ascribed to the trapping of injected holes at the region close to the cathode side. Influence of space charge formation, photoconductive gain, contribution of shallow and deep levels to photocurrent-voltage characteristics were numerically simulated. According to the measurements and calculations, recent principles used at the evaluation of detector properties, mainly the mobility-lifetime product, via the photoconductivity are critically assessed.

Low-Temperature Annealing of CdZnTeSe under Bias

“…Moreover, the almost perfectly linear profiles of the electric field in Figure 2 sign the charging by carrier depletion. On the other hand, the carrier injection would produce curves deviating from linear profiles as predicted by the theory of the Space Charge Limited Currents [ 23 , 24 ]. Consequently, the blocking cathode may be considered as the primary attribute responsible for the positive space charge formation in the sample before annealing—step 0.…”

“…We tested the validity of the presented physical model by numerical simulation illustrating the oscillatory character of the charge and resistance shown in Figure 2 b,d and Figure 3 c, respectively. The calculations were done with the homemade code [ 23 , 25 ] solving the drift-diffusion and Poisson’s equations. We defined the defect structure of the bulk by trial parameters: Fermi energy eV, one electron trap with the density cm localized below at the energy eV, and one hole trap above with the density cm at the energy eV.…”

“…We defined the defect structure of the bulk by trial parameters: Fermi energy eV, one electron trap with the density cm localized below at the energy eV, and one hole trap above with the density cm at the energy eV. Since we investigated only the steady state here, the respective capture cross sections cannot be determined [ 23 ]. The effect of the annealing was simulated by tuning transfer rates defining the source of carriers in both contacts [ 23 ].…”

“…Since we investigated only the steady state here, the respective capture cross sections cannot be determined [ 23 ]. The effect of the annealing was simulated by tuning transfer rates defining the source of carriers in both contacts [ 23 ]. We used flat bands at the simulations since the information on the band bending is not accessible.…”

Stable photocurrent–voltage characteristics of perovskite single crystal detectors obtained by pulsed bias

“…[10,11] To study the photocurrent-voltage characteristics of perovskites, it is necessary to gradually increase the bias voltage for a given light illumination with the aim of saturating the photocurrent. [12,13] This requires the material to exhibit excellent stability under high bias conditions.…”