Investigation of extended defects in cadmium zinc telluride crystals grown by vertical gradient freeze (VGF) technique

Doğru, Çiğdem
Cadmium Zinc Telluride (CZT) crystal is a promising material due to its high atomic number, room temperature operability and low leakage current. It is used in many important applications such as room temperature gamma ray and X-ray detectors, medical imaging spectrometers. In addition, CdZnTe crystal has been accepted as an excellent substrate for the growth of Hg1-yCdyTe epitaxial layer, which is used for the fabrication of advanced infrared focal plane arrays (IR FPA) due to the good lattice match with Hg1-yCdyTe. However, CZT crystal has a strong tendency to generate defects such as dislocations, inclusions, precipitates, twins and sub-grain boundaries. One of the most successful approaches in identifying the nature and the amount of these defects is based on etching the surface of the crystal. This thesis focuses on different etching studies conducted on Cd0.96Zn0.04Te substrates to reveal the etch-pit formation with the purpose of determining the total defect density throughout the substrate surface. Extensive studies on different etching methods such as Nakagawa, Everson, Inoue and Bagai etchants have been carried to investigate the dislocation density and thus the CZT crystal quality. Following to each etching process, CZT crystals have been characterized by a series of versatile characterization techniques such as Energy Dispersive X-ray (EDS) Spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The kinetics of each etchant on different substrate orientation was studied and the etch rates were determined. Etch pit formation and its dependence on surface orientation were identified through extensive experiments.


Nanoscale surface finishing studies and characterizations of cadmium zinc telluride crystals
Kabukcuoğlu, Merve Pınar; Turan, Raşit; Department of Physics (2016)
Cadmium Zinc Telluride (Cd1-xZnxTe, CdZnTe) crystals are used in two different applications depending on Zinc (Zn) concentrations. CdZnTe crystals are one of the most promising materials for X-ray and gamma-ray detector applications due to unique material properties such as high atomic number and high resistivity. Wide band gap and high stopping potential of CdZnTe crystals allow operation at room temperature for high performance detectors with several applications including medical imaging, astronomy, and ...
Investigation of silver-induced crystallization of germanium thin films fabricated on different substrates
Kabacelik, Ismail; KULAKCI, MUSTAFA; Turan, Raşit (2015-06-01)
Silver-induced crystallizations of amorphous germanium (alpha-Ge) thin films were fabricated through electron beam evaporation on crystalline silicon (c-Si) (100), aluminum-doped zinc oxide (AZO), and glass substrates at room temperature. The solid-phase crystallization (SPC) of alpha-Ge films was investigated for various post-annealing temperatures between 300 and 500 degrees C for 60 min. Two crystallization approaches were compared: SPC and metal-induced crystallization (MIC). The structural properties o...
Optimization of chemical polishing by bromine-alcohol for detector-grade CdZnTe crystals and its effect on contacts
Ünal, Mustafa; Balbaşı, Özden Başar; Ergunt, H Yasin; Turan, Raşit (2018-08-19)
Cadmium Zinc Telluride (CdZnTe) is a good candidate for detection of x-ray and gamma-rays due to its high atomic number and large bandgap. CdZnTe is a II-VI group semiconductor and by changing ZnTe concentration, its properties can be altered. CdZnTe crystals having 4% ZnTe is commonly used as a substrate for Mercury Cadmium Telluride (HgCdTe) which is an important absorbing material for infrared imaging applications. For x-ray and gamma-ray detection, on the other hand, ZnTe concentration is kept around 10...
Investigation of the larger scale tungsten production by the electrochemical reduction technique
Özdemir, Furkan; Erdoğan, Metehan; Elmadağlı, Mustafa; Karakaya, İshak (null; 2016-11-01)
Hydrogen reduction of WO3 is the major industrial process in tungsten production. A promising cost and energy efficient method was recently reported [1-3] for direct electrochemical production of tungsten from CaWO4 (scheelite) which is estimated as the two third of the all tungsten reserves of the world. Following the above mentioned patent, several studies verified the production of metallic tungsten by electrochemical reduction of calcium tungstate in the laboratory. This study investigates the applicati...
Development of Inorganic Silicone Polymers from Silica Fume
Erdoğan, Sinan Turhan; Tokyay, Mustafa (2012-10-05)
Geopolymers, inorganic materials with polymer-like repeating units containing silicon, aluminum, and oxygen, in 1-, 2-, or 3-dimensions, have been gaining popularity. While most research has focused on rigid, higher- strength geopolymers with mechanical properties similar to those of Portland cement concrete, there also exists a silicon-rich class of geopolymers which is more polymer-like, with lower strength and stiffness, and greater strain capacity but still having thermal resistance much superior to tra...
Citation Formats
Ç. Doğru, “Investigation of extended defects in cadmium zinc telluride crystals grown by vertical gradient freeze (VGF) technique,” M.S. - Master of Science, Middle East Technical University, 2015.