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Optical methods for characterization of semiconductor radiation detectors
Pekárková, Katarína ; Belas, Eduard (advisor) ; Humlíček, Josef (referee) ; Ledinský, Martin (referee)
CdZnTe and perovskites are promising materials for radiation detectors. Here, we address the main obstacles to their application, CdZnTe charging, and perovskite stability by photocurrent measurements. In the first part, models describing space-charge-limited photocurrents are developed, and an excellent agreement with measured data is obtained. The Drift-diffusion model provided us with a detailed defect analysis of CdZnTe. A linear rise of photocurrent at low voltage originates in the trapping of injected holes close to the cathode. We propose a simple procedure to evaluate space-charge density from photocurrents. The influence of space-charge, photoconductive gain, and shallow levels result in inaccurate evaluation of mobility-lifetime product via photoconductivity. The second part focuses on light-induced changes in perovskites. Laser-induced transient current measurements show improvements in hole lifetime and surface recombination in CH3NH3PbBr3 single crystals. We further study phase segregation in mixed-halide perovskites by Fourier-Transform photocurrent spectroscopy. The recorded gradual formation of an I-rich phase correlates with an increase in deep defect concentration, which we attribute to charged iodide interstitials. Phase segregation is associated with iodide migration through interstitial...
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