Optical and electrical properties of SiO2 and CaSiO3

Abstract

Wide band gap materials are of very high research interest due to their wide applications in semiconductor industry. SiO2 and CaSiO3, both can be used as the topmost layer of the solar cell because it is observed in literature survey that their optical properties can be modified by the action of temperature and these modified samples may exhibit some interesting properties by doping suitable material. Keeping all these in view, in present work, samples of SiO2 and CaSiO3 has been prepared by sol gel method and hydrothermal method respectively. Purity of these samples has been confirmed by analyzing their XRD pattern and indexing was done for miller planes corresponding to each peak. The band gap for all presently studied samples has been determined through diffuse reflectance spectroscopy (DRS) based on the formalism of Kubelka-Munk function and Tauc relation.The band gap of SiO2 Samples was observed to be decreasing with increase in Annealing temperature making it suitable to use as the top most layer of solar cell if band gap can further be decreased by doping/defects or other means. The band gap of CaSiO3 has been observed to be increasing with increase in Annealing temperature; it proves that we will need some other method such as doping/defects to make it suitable so that it can be used in increasing the efficiency of solar cell. Defect states (extra state at lower energy) are clearly visible in DRS absorption plot, by comparing this plot with theoretical calculations; one can find the exact amount (percentage) of oxygen defects produced by annealing at different temperatures. Keeping this in view, we have performed Density functional to generate Density of states (DOS) and optical spectra using WIEN2k code. A first-principle calculation has been carried out using local density Approximations (LDA). To validate our experimental results, we have performed first principle calculations and the results are found to be in accordance with the experimental data.