Halide perovskites have undergone remarkable developments as highly efficient optoelectronic materials for a variety of applications. Several studies indicated the critical role of defects on the performance of perovskite devices. However, the parameters of defects and their interplay with free charge carriers remain unclear. In this study, we explored the dynamics of free holes in methylammonium lead tribromide (MAPbBr₃) single crystals using the time-of-flight (ToF) current spectroscopy. By combining ToF spectroscopy and Monte Carlo simulation, three energy states were detected in the bandgap of MAPbBr₃. In addition, we found the trapping and detrapping rates of free holes ranging from a few microseconds to hundreds of microseconds. Contrary to previous studies, we revealed a strong detrapping activity of traps. We showed that these traps substantially affect the transport properties of MAPbBr₃, including mobility and mobility-lifetime product. Our results provide an insight on charge transport properties of perovskite semiconductors.

The electron- and hole-transport properties in cadmium zinc telluride selenide (CZTS) crystals are studied using a laser-induced transient-current technique with pulsed and dc bias. The internal electric field profile and velocity of surface recombination are determined by Monte Carlo simulations of electron and hole transient currents combined with a numerical solution of the drift-diffusion equation coupled with Poisson’s equation. Electron and hole drift mobilities of ${\mu }_e$ = 830 ${\mathrm{cm}}^2$/Vs and ${\mu }_h$ = 40 ${\mathrm{cm}}^2$/Vs, respectively, are determined. We also develop a simple technique for evaluating surface recombination directly from measured current waveforms without the need for numerical simulation. The good quality of the prepared detector at pulsed bias, with electron- and hole-mobility-lifetime products of $(\mu \tau {)}_e$ = 1.9 × ${10}^{-3}$ ${\mathrm{cm}}^2$/V and $(\mu \tau {)}_h$ = 1.4 × ${10}^{-4}$ ${\mathrm{cm}}^2$/V, respectively, are observed. The formation of a positive space charge, originating from hole injection combined with a recombination level, is found. We observe a significant position dependence of the lifetime of electrons and holes in dc bias due to hole injection. The experiment is successfully fitted by a simple model dominated by a single deep recombination level with an energy of $E_t=E_C-0.73\mathrm{eV}$; concentration of 7.3 × ${10}^{11}$ ${\mathrm{cm}}^{-3}$; and electron- and hole-capture cross sections of 3.5 × ${10}^{-14}{\mathrm{cm}}^2$ and 6.5 × ${10}^{-14}{\mathrm{cm}}^2$, respectively.

Cadmium telluride (CdTe) and its compounds are the materials of choice for producing industrial quality hard x-ray and gamma ray detectors with high spectral resolution and signal-to-noise ratio. However, optimization of the growth process still proves challenging as the yield is small due to inhomogeneities in the material parameters. Here we investigated the influence of inhomogeneous resistivity on charge collection efficiency of CdZnTe radiation detectors operating at high photon fluxes of incoming radiation. We applied a complex of experimental methods—contactless resistivity and photoconductivity mapping, photoluminescence and laser-induced transient current technique. We observed that the charge collection efficiency at low fluxes is nearly independent of resistivity, while at high fluxes the performance of high resistivity part substantially decreases when compared to the lower resistivity part. This behavior is explained by characteristic evolution of defect structure attaining shallow defect self-compensation during the cooling of the solidified crystal. Instabilities at impurity segregation and temperature gradients at the crystal growth cause different concentration of defects that manifest themselves as deep energy levels within the material bandgap. The defect self-compensation is successfully simulated by theoretical model considering defect reactions in tellurium-saturated CdZnTe.

Semi-insulating CdTe and CdZnTe crystals fabricated into pixelated sensors and integrated into radiation detection modules have demonstrated a remarkable ability to operate under rapidly changing X-ray irradiation environments. Such challenging conditions are required by all photon-counting-based applications, including medical computed tomography (CT), airport scanners, and non-destructive testing (NDT). Although, maximum flux rates and operating conditions differ in each case. In this paper, we investigated the possibility of using the detector under high-flux X-ray irradiation with a low electric field satisfactory for maintaining good counting operation. We numerically simulated electric field profiles visualized via Pockels effect measurement in a detector affected by high-flux polarization. Solving coupled drift–diffusion and Poisson’s equations, we defined the defect model, consistently depicting polarization. Subsequently, we simulated the charge transport and evaluated the collected charge, including the construction of an X-ray spectrum on a commercial 2-mm-thick pixelated CdZnTe detector with 330 µm pixel pitch used in spectral CT applications. We analyzed the effect of allied electronics on the quality of the spectrum and suggested setup optimization to improve the shape of the spectrum.

In this work, we studied the free-carrier transport properties and space-charge formation/polarization in a CdZnTe bar-shaped radiation detector using the Laser-Induced Transient Current technique. We found out that a steady-state space charge ranging from 8 × 108 to 2.1 × 109 cm−3 is formed throughout the detector at about 0.5 s following biasing. The measured current waveforms were modeled by Monte Carlo simulations after taking into account the electric and weighting fields inside the detector and shielding box. Modeling of the unpolarized waveforms revealed an exceptionally high electron mobility-lifetime product μeτe≥0.095cm2V−1. The observed formation of positive space charge in the biased detector and linear scaling of the current waveform shapes on applied bias revealed that the detector polarization is attributed to carrier injection at the anode. Measurements in pulsed and DC bias in modified electrode geometry proved the surface-charge formation.

In this paper we compare suitability of three different semi-insulating bulk silicon carbide (SiC) materials for fabrication of radiation detectors. We prepared planar sensors with various metal contact combination and characterized detector quality by the alpha spectroscopy and I-V characteristic measurements. We observed that 4H-SiC material from the II-VI company is not suitable for radiation detector fabrication due to high concentration of vanadium doping. We also present a poor charge collection efficiency of the 4H-SiC Norstel material due to high concentration of residual impurities and we evaluated low mobility-lifetime product (alpha)= 3.5E-7 cm2/V from the alpha spectroscopy. We demonstrate that the 4H-SiC material from the Cree company is the best candidate for the production of radiation detectors. We evaluated mobility-lifetime product (alpha)= 5.4E-6 cm2/V using AuTi/SiC/TiAu contact structure.