Structural and optical properties of CdTe thin film: A detailed investigation using optical absorption, XRD, and Raman spectroscopies

Abstract

Physical vapor deposition (PVD) is used to grow CdTe thin films of different thicknesses on glass substrates. The characterization of the samples is then investigated optically and structurally. Three experimental techniques were used in this study; optical absorption (ABS), Raman, and X-ray diffraction (XRD) spectroscopies. In optical ABS spectroscopy, the Urbach energy related to the width of long-wavelength tail decreases from 827 to 585 meV as the thickness increases from 100 to 500 nm, respectively. The thickness-dependent particle size was calculated using the value of the size-dependent optical absorption edge energy. A shift of 710 meV in the ABS edge energy takes place as the thickness increases from 100 to 500 nm. Thickness-dependent shifting and widening of XRD line is presumably due to the size effect and strain. Relative to the phonon frequency of bulk CdTe crystal, a thickness-dependent blueshift was observed in Raman spectra for the Longitudinal Optical (LO) phonon frequency, while a redshift for the longitudinal acoustic (LA) and transverse optical (TO) phonon frequencies is observed. In the present work, the results of optical absorption, XRD, and Raman analyses are combined in order to study the effect of particle-size evolution, thickness-dependent strain, and structural disorder. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim