Investigation of electronic properties of detector grade cadmium zinc telluride crystals and development of electrodes for X-ray and gamma ray applications

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2019
Bender, Deniz
In the last three decades, we have witnessed extensive research activities on Cadmium Zinc Telluride (CdZnTe or CZT) crystals to be used as a part of radiation detector systems in different application areas including astrophysics, medical science and security devices. The accompanied developments such as increased ability to control the bulk growth of CZT crystals, advances in microelectronics and improvements in data-acquisition methods have all paved the way for flexible configurations of multiple pixel modules consisted of CZT detectors. Being a II-VI compound semiconductor, CZT appears to be suitable for room temperature operation with a high spectroscopic resolution. The intrinsic properties CZT crystal such as wide bandgap, high resistivity and high atomic number make it very useful in these applications. Although the resistivity of CdZnTe crystal is relatively high (ρ > 108 Ω cm), cracks formed during lapping/polishing processes or surface contamination make surface resistivity lower, leading to surface leakage current problems. To be able to use CZT crystals in X-ray and gamma-ray applications, leakage current should be minimized. In this thesis study, CZT detectors from different ingots produced at METU Crystal Growth Laboratory (GCL), including one with Indium doped and also from a commercial crystal, were produced and current-voltage (I-V) characterizations were completed with various electrode designs. Main focus was to investigate the current-voltage behavior of metal-semiconductor interface formed on the detector crystals. In addition to I-V measurements, the crystal grown and prepared for detector application was characterized by different methods such as X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM).
Citation Formats
D. Bender, “Investigation of electronic properties of detector grade cadmium zinc telluride crystals and development of electrodes for X-ray and gamma ray applications,” M.S. - Master of Science, Middle East Technical University, 2019.