Optical and electrical anisotropies in Cu2ZnSnS4 and Cu2MgSnS4 thin films deposited by thermal evaporation at obliquely incident angle

In this work, CMTS (Cu2MgSnS4) and CZTS (Cu2ZnSnS4) thin films have been deposited at room temperature by thermal evaporation at different oblique incident angles gamma = 00 degrees, 30 degrees, 60 degrees, 75 degrees and 85 degrees. XRD and Raman measurements were carried out to study the structural properties. The morphological properties and compositional analysis of the synthesised thin films were analysed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The optical and electrical properties of the resulting films were evaluated by UV-Vis-NIR spectrophotometry and 4-point probes, respectively. The surface and cross-section of the films were visualised by scanning electron microscopy (SEM). The as-deposited films exhibited a tilted columnar structure in the direction of incident flux. The dependence of the optical properties on the deposition angle was investigated over a wavelength range from 300 to 1800 nm. The transmission spectra (T(lambda)) indicate that the number of fringes decreases as the incident angle increases from 00 degrees to 85 degrees for both materials. The in-plane birefringence of CZTS and CMTS indicates that the optical anisotropy is maximal for an incident angle of gamma=60 degrees. Similarly, the maximum electrical anisotropy is observed for the angle of incidence of 60 degrees. In addition, a strong dependence of the anisotropy, film thickness and porosity on the deposition angle was found for both materials. It appears that the 60 degrees angle of incidence is critical for enhancing the anisotropy properties. Accordingly, the oblique angle of incidence process offers a promising route to producing columnar nanostructures with improved anisotropy properties.