Point defect characterization in room-temperature radiation detectors (cadmium zinc telluride, cadmium manganese telluride, thallium bromide) and semiconductor materials useful as photovoltaic devices

In this research a comprehensive study is carried out on material properties and performance of semi-insulating and semiconductor materials such as CdZnTe, CdMnTe, TlBr, and GeS2, CuInS2, CuInSe 2, useful as room temperature radiation detectors and as photovoltaic/phase memory materials, respectively. Particular emphasis is placed on the characterization of crystal point defects within the bandgap, which mostly contribute to the degradation of the detectors. Next, a correlation between these defects and the carrier life time is established and is related to device performance. Different deep traps and their probable origins are identified. It was concluded that deep traps are important to obtain highly resistive materials for room temperature devices. An excess of these deep traps causes a degradation of the device detection performance by lowering the carrier life time. In addition, the study focuses on the structural and chemical analysis of the photovoltaic cells, charge transport properties, and the electrical, photo and gamma radiation response of the detectors and devices. A variety of characterization techniques are employed successfully, such as: Deep Level Transient Spectroscopy (DLTS), Photoluminescence (PL) and Thermal Electron Emission (TEES) for the point defect characterization, IR microscopy for the microstructure and extended defects in the crystal, I/V and C/V measurements of the electrical response and resistivity of the material, gamma-ray spectroscopy for the radiation detection response, photocurrent measurements for testing the photo sensitivity of the detectors and solar cells, and Energy Dispersive Spectroscopy (EDS), Raman spectroscopy and SEM for the chemical analysis and structural/surface studies of the thin film.