Research On Growth And Optical Properties Of The Designed (Si/Ge)_xZnO Thin Films For Solar Cell

In this study, on the base of the present status and future development of semiconductor materials for solar cells, we have carried out the work to compose film structures of Si-based materials by theoretical analysis and experimental methods, which have potential application in modules of solar cells. The processing, features of microstructure and optical properties of the designed Si-based thin films have been studied in detail by employing methods of XRD, SEM, AFM, TEM, Raman, FTIR, UV-Vis, PL, and Ellipsometry Spectroscopy(SE).At first, the processing of Magnetron Sputtering, including parameters of gas pressure(Pg), input power(Pin), substrate temperature(T) and film thickness(Th), on the microstructure and optical properties of Si film have been discussed. The optimized growth parameters as follows have been achieved for depositing Si films: Pg=1.0Pa; T=300～400℃; and Pin=90～100W.According to the principle of Energy Bandgap Thoery and Optical Absorption Principle of semiconductor materials, four different structures have been designed as (a)Quartz/Ge/Si; (b)Quartz/(Ge/Si)3; (c)Quartz/ZnO/Ge/Si; (d)Quartz/ZnO/(Ge/Si)3, and then deposited them by Magnetron Sputtering using the optimized processing. The information of microstructure, optical properties and relevant mechanisms of the as-prepared and annealed samples has been studied. Results have demonstrated that the properties of optical absorption and photoluminescence of Quartz/(Ge/Si)3 are better than those of Quartz/Ge/Si. In the light of relevant reaction mechanisms betweet ZnO buffer layer and Si/Ge films, it is clear that the introduction of ZnO influences the roughness of Si/Ge film in reverse direction for as-prepared and annealed samples, respectively. In addition, it also enhances the crystallization temperature of Si/Ge film. The main reason lies that ZnO has reacted with Ge to form a new compound of Zn2GeO4 leading to the volume of Ge decreasing largely. We have proposed a solution to control the reaction by reducing the thickness of Ge sublayer and increasing the number of Si/Ge layer synchronously.Finally, a novel structure of"Amorphous-Polycrystalline/Nanocrystalline", (Si/Ge)xZnO thin films, has been fabricated successfully by combing Magnetron Sputtering and Thermal Annealing technologies. Features of film morphology, interfaces, microstructure, crystallization behaviors and optical properties have been investigated, which illustrates that nanocrystals of Ge has direct energy band gap in our experiment, and Si-based multilayers with broad wavelength absorption of visible light, high intersity of photoluminescence and low density of defect recombination centers has been developed. It is of great significance for its applications in photovoltaic and optoelectronic aeras.