Influence of Annealing Temperature on the Properties of SILAR Deposited CdSe/ZnSe Superlattice Thin Films for Optoelectronic Applications

Abstract

In this work, superlattice thin films of CdSe/ZnSe were fabricated on a non-conductive glass substrate using the successive ionic layer adsorption reaction (SILAR) method to investigate their properties for possible optoelectronic applications. The SILAR process involved a total cycle time of 100 s for a complete SILAR cycle with a total of 12 cycles made by depositing alternative layers of CdSe and ZnSe. The deposited thin films were annealed at different temperatures and characterized to determine their optical, elemental, morphological and structural properties using UV-Vis spectroscopy, Scanning electron microscope (SEM)/energy dispersive X-ray spectroscope (EDS) and X-ray diffraction techniques (XRD). The results of the characterizations revealed that optical properties of the films such as absorbance, reflectance, refractive index and extinction coefficient are low but increased as the annealing temperature increases. The bandgap energy was found to decrease from 2.50 eV to 1.90 eV for as-deposited film and those annealed between 373 K and 523 K. film thickness was found to range from 130.169 nm to 254.441 nm. The EDS results showed that the target elements such as Cd, Zn, Se and other elements traceable to the nature of substrate used were found to be present in the deposited thin film samples. The results of the XRD showed that the thin films are polycrystalline and the diffraction peaks are influenced by annealing of the sample at a higher temperature such as 523 K. The crystal parameters such as crystallite size, dislocation density and micro-strain of the film at 523 K were found to be 5.546 nm, 3.25 × 10¹⁶ l/m² and 1.13 × 10⁻². The SEM results showed that the CdSe/ZnSe superlattice films were composed of tiny nanoparticles of different dimensions and sizes with hollow which increased as the annealing temperature increased from 432 K to 523 K. Possible applications of the deposited superlattice thin films in solar cells and optoelectronic devices were established by virtue of their bandgap energy and other properties.