Influence of angle deposition on the properties of ZnTe thin films prepared by thermal evaporation

Thin films of ZnTe were deposited at angles of 0°, 20°, 40°, 60° and 80° by thermal evaporation. The chemical, structural, morphological, optical, and photocurrent properties of ZnTe thin films were investigated. The elemental composition of the films was investigated by energy dispersive x-ray spectroscopy (EDX) and x-ray photoelectron spectroscopy (XPS). EDX and XPS analyses showed that at lower angles (0° and 20°), the deposited films were Te-rich, at 40°, the deposited film was nearly stoichiometric; and at higher angles (60° and 80°), the deposited films were Zn-rich. X-ray diffraction (XRD) analysis showed that all films were polycrystalline. X-ray diffraction patterns showed that lower-angles-deposited films had an extra peak at 2θ = 36.47° that belongs to Te element. Atomic force microscopy analysis revealed that the surface roughness of films was increased by increasing the deposition angle from 0° to 80° because shadowing effect raised due to an oblique angle. It was observed that higher-angles-deposited films (ZnTe-60°, and ZnTe-80°) showed less transmittance and high reflectance compared to lower-angles-deposited films because of high metallic Zn content in these films. Current-voltage (I-V) measurements showed that nearly stoichiometric (ZnTe-40°) film showed better photocurrent response compared to non-stoichiometric films (ZnTe-0°, ZnTe-20°, ZnTe-60°, and ZnTe-80°).