Mr. Özden Basar Balbasi Profile

Özden Basar Balbasi

at Middle East Technical University

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Publications (2)

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Proceedings Article | 18 September 2018 Presentation

Optimization of chemical polishing by bromine-alcohol for detector-grade CdZnTe crystals and its effect on contacts (Conference Presentation)

Mustafa Ünal, Deniz Bender, Özden Balbasi, Merve Kabukcuoglu, Yasin Ergunt, Rasit Turan

Proceedings Volume 10762, 107620U (2018) https://doi.org/10.1117/12.2323097

KEYWORDS: Polishing, Sensors, Crystals

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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%. Due to high resistivity of CdZnTe crystals, preparation of surfaces prior to deposition of electrodes is important. After cutting and mechanical polishing, subsurface damages are observed on the crystals, which have a negative effect on the resistivity of the crystal near to the surface alongside with the dangling bonds on the surface. Decrease in the resistivity results in high leakage current that hinders the collection of electrons produced by absorption of photons. In addition, to have a strong bonding with electrode metal, surface should be clean from contaminants like oxygen and carbon. Achieving clean surface with low leakage current can be achieved by employment of chemical polishing step prior to electrode deposition. Bromine-alcohol solutions are used for chemical polishing without much control over the etching conditions. In this study, we report on the results of optimization study of chemical polishing by bromine-alcohol. Different alcohols (methanol, ethanol, propanol) were employed with different concentrations and etching durations. In addition, etching is conducted for different orientations to examine orientation dependency of the solution.

Proceedings Article | 13 September 2018 Presentation + Paper

CdZnTe bulk crystal growth and temperature modeling studies at METU-CGL

Özden Balbaşı, Yasin Ergunt, Çiğdem Doğru, Merve Kabukcuoglu, Mustafa Ünal, Mehmet Parlak, Rasit Turan

Proceedings Volume 10762, 107620R (2018) https://doi.org/10.1117/12.2323409

KEYWORDS: X-ray detectors, Modeling and simulation, Group II-VI semiconductors, Crystals, Interfaces, Crystallography, Cadmium, Quartz, Tellurium, Heat flux, Zinc

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Cadmium Zinc Telluride (CD_1-xZn_xTe has become a crucial material for x-ray and gamma ray detection due to its wide band-gap, high atomic number and high density, which offer high efficiency and sharp spectroscopic resolution at room temperature. In addition, due to being lattice matched, it can also be used as substrate for the epitaxial growth of HgCdTe that can be used for infrared detection with high resolution. Hence, increasing the single crystal yield of CdZnTe from the grown ingot gained importance for the development of such detectors. In this study, a combination of modeling and experimental approaches has been developed in order to obtain high quality CdZnTe bulk crystals with good single crystal yield. A multi-zone Vertical Gradient Freeze (VGF) furnace was used for CdZnTe growth experiments. A global temperature model of the multi-zone furnace including complete geometry was employed using CrysMAS crystal growth modeling software. The correlation studies between the model and experimental behavior of the furnace are discussed in order to create a reliable model for temperature predictions. Temperature models were also included solid-liquid interface study in order to observe the interface shape at various stages of growth which would provide valuable insight about the quality and the yield of the ingot. Growth parameters and crucible geometries were estimated by CrysMAS simulations and interchanged between experiments. Effectiveness of temperature models and simulations was supported by experimental results such as single-crystalline yield, grain evolution and crystalline quality comparison by DCRC measurements of five successful crystal growths with moderate single crystal grain sizes.

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