Investigating the effect of Te on the structural and physical properties of CdSe films for optoelectronic applications

Abstract

Thermal evaporation was used to fabricate (CdSe)1−x(Te)x (0 at% ≤x ≤ 0.2 at%) films on ultra-clean substrates made of glass. The films in our study were deposited at room temperature in an evacuated chamber of approximately 3 × 105 mbar with a deposition rate of 2.8–2.3 Å. The thin films initially had a polycrystalline structure with a cubic crystal system, transitioning to an amorphous structure at 0.1 % Te content, before returning to a polycrystalline structure with a hexagonal crystal system at higher Te content. The microstructural parameters evaluated included dislocation density) δ (, lattice strain (ε), lattice constant (a), and average crystallite size (Davg). Scanning electron microscopy indicated that the grain size of the samples was around 10–60 nm. Swanepoel’s relation was applied to determine the film thickness (d) and refractive index (n) of the samples at specific points on the wavelength spectrum. Furthermore, the refractive index (n), and extinction coefficient (k) were calculated as functions of wavelength using Cauchy’s relation. The optical band gap (Eg) showed a slightly decreased, and the Urbach energy (Eu) increased with the Te ratio. Based on the Fourier transform infrared absorption spectrum, the CdSe vibrational mode was found to exist between 400 cm−1 and 800 cm−1. Additionally, the Raman spectrum of CdSe thin films was presented to enhance our understanding of the compounds vibrational characteristics. By carefully selecting the ideal ratio of transition metal dopants, our study opens the door to enhancing the physical properties of CdSe for use in optoelectronic devices.