Structural, optical and electrical characterization of CDSEXTE1-X thin films

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2020
Demir, Merve
The aim of this study is to investigate the structural, optical and electrical properties of ternary CdSexTe1-x thin films. CdTe and CdSe thin films are being used in solar cells due to their favorable direct band gaps of 1.5eV and 1.7eV, respectively. Moreover, having high absorption coefficients provide an important role to CdTe and CdSe films as an absorber layer. Therefore, by mixing these two films, properties of resultant ternary CdSexTe1-x alloy can be optimized for solar cell applications. Chemical similarities between Te and Se and the structural similarities between CdTe and CdSe provides broad range of solid solubility. By changing the ratio of Se to Te, structural, optical and electrical properties of CdSexTe1-x can be tuned and hence, promising results can be obtain for solar energy conversion technology. Ternary CdSexTe1-x thin films deposited by stacking electron beam evaporated CdTe layers on top of thermally evaporated CdSe layers. In order to identify the effects of varying stoichiometry on structure, CdSexTe1-x films with different constituent ratios were prepared. In addition, effects of the post deposition treatment, specifically post annealing, were analyzed and the process were optimized. The structural properties of the films were investigated by X-ray diffraction (XRD), Raman spectroscopy and energy-dispersive X-ray diffraction (EDX). For optical characterization of the films, UV-Vis spectroscopy was employed and the band gap values of CdSexTe1-x thin films were determined. Electrical characterization includes temperature dependent conductivity and photoconductivity measurements. Moreover, surface structure of the CdSexTe1-x thin films was examined by atomic force microscope (AFM) and scanning electron microscope (SEM). It was discovered that formation of CdSexTe1-x thin films can be observed by post heat treatment at 400°C for 60 minutes. XRD and Raman spectroscopy results showed that films have polycrystalline nature and crystallinity increase with increasing annealing temperature. However, it is found that in order to preserve desired stoichiometry the upper limit should be set for annealing procedure. Otherwise, Se evaporation at high temperatures leads to variations in composition of the films uncontrollably. Furthermore, band gap of CdSexTe1-x thin films can take values between 1.4 eV≤E_g≤1.7 eV and conductvity values on the order of 10-7 (Ω.cm)-1.

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Citation Formats
M. Demir, “Structural, optical and electrical characterization of CDSEXTE1-X thin films,” Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Physics., Middle East Technical University, 2020.