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.
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.