Effects of electrodeposition parameters on characteristics of CdTe thin films investigated by X-ray photoelectron spectroscopy analysis

• Main Authors: Yu-Jung Hsu, 許育榮
• Other Authors: Chia-Hua Huang
• Format: Others
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/17700887372280249900

碩士 === 國立東華大學 === 電機工程學系 === 103 === The CdTe thin films were deposited with the acidic electrolytes consisted of CdSO4, TeO2, and H2SO4 by using a three-electrode electrodeposition system. The effects of deposition potentials, temperatures, and pH values on the as-deposited CdTe thin films were mainly investigated by using X-ray photoelectron spectroscopy (XPS). CdTe thin films were electrodeposited at different potentials between -550mV and -625mV, temperatures of 75°C~90°C, and pH values of 1.7~2.1. The pH values were adjusted by using the concentrations of H2SO4. The surface morphologies and the cross-section views, and the crystalline structures of CdTe films were characterized by field emission secondary electron microscope (FE-SEM) and X-ray diffraction analyzer (XRD), respectively. Furthermore, the binding energy of elements and the compositions of surface region and along the depth of CdTe films were analyzed by XPS measurements. The XPS results showed that the CdTe films contained the Te, Cd, and a small amount of oxygen, where the atomic ratios of Te to Cd were greater than unity. The analyses of the surface and depth compositions showed that the oxygen contents at the surface were obviously greater than that in the bulk, and the uniform distributions of Cd and Te were observed inside the films. Along with the analysis of electrochemical deposition reaction, the identification of the compounds of as-deposited films analyzed from the XPS spectra of surface region and along the depth of CdTe films by using peak deconvolution of curve fitting suggested that the electrodeposited CdTe films comprised the CdTe, TeO2, and Tex. The XPS results showed that the ratios of Cd/Te decreased with the increase of deposition potentials or temperatures, and the decrease of pH values. From the SEM and XRD results, the reduction of deposition potentials, increase of temperatures, and decrease of pH values resulted in the increase of grain aggregation around the surface region, the increase of thickness, narrowing of full width at half maximum (FWHM), the improvement of crystallinity, and the increase of grain size. Among the given deposition conditions, the deposition temperatures were a dominant factor impacting the surface morphology, film thickness, crystallinity, and Cd/Te ratios of CdTe films.