Influence of deposition angle on structural, optical, and electronic properties of zinc sulfide nano-layers and optical relation between Kramers-Kronig and DFT calculations

Abstract

Nano-layers of zinc sulfide on glass substrates were prepared by physical vapor deposition (PVD) method, under high vacuum (HV) conditions, with different deposition angles of 0, 25, and 35° at 300 K temperature. Thickness of the layers was measured 73 nm, by quartz crystal method. The nanostructures of the films were obtained, by using X-ray diffraction (XRD) and atomic force microscopy (AFM) methods. Optical reflectance and transmittance of the layers were measured in the wavelength range of 300–1100 nm by a spectrophotometer. Kramers-Kronig relations were used to calculate the optical constants. Fraction of voids were calculated by Aspens theory. By increasing deposition angle, more voids are formed on layers and structure of layers has changed from homogeneous to heterogeneous. In this work, the influence of deposition angle on optical properties, structural changes, and the relation between nano structures and optical properties of ZnS nano-layers are investigated. The samples prepared under higher deposition angles showed smaller absorption coefficient. Optical properties are studied using full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). In this approach, the generalized gradient approximation (GGA) was used for the exchange-correlation potential calculation. The calculation results are compared with experimental data. Possible energy transitions are also reported. An average value of 2.40-eV band gap for the layers produced in this work has been deduced which is also calculated from FP-LAPW method, and obtained about 2.2 eV.