Research On Preparation And Properties Of SiN/(Si/Ge)_x Thin Films For Solar Cell

In this study, based on the present status and future development of semiconductor materials for solar cell applications, SiN/(Si/Ge)x multilayer films were prepared by magnetron sputtering process. The microstructure and optical properties of the films were investigated by XRD, SEM, Raman, FTIR, UV-VIS and PL methods.At first, the influences of different processing parameters of magnetron reaction sputtering, including substrate temperature, input power, gas pressure and ratio of gas flowrate, on the film thickness, density, microstructure and optical properties of SiN films were thoroughly discussed. The optimized depositing parameters of SiN films were obtained, namely substrate temperature: 450℃, input power: 100W, gas pressure: 0.5Pa, N2/Ar ratio: 6/16. With these parameters, the optical band gap of producted SiN film is 4.62eV, which is close to 4.6eV, that of stoichiometric Si3N4. As-sputtered SiN films were found mostly amorphous and their optical transmittance is relatively higher in the ultraviolet-visible region. The SiN thin films deposited by RF magnetron reaction sputtering contain about 3~5 at.% hydrogen according to Lanford and Rand'method.Secondly, by combining the principle of energy bandgap theory and optical absorption principle of semiconductor materials as well as thermal annealing technology, a novel structure of"amorphous-polycrystalline/nanocrystalline"a-Si/a-Ge/(Si/Ge)3 thin films were fabricated. The morphology, interfaces, microstructure, crystallization behaviors and optical properties were investigated. The results illustrate that nanocrystalline of Ge is featured with direct energy band gap, as well as the prepared Si-based multilayer film is with broad wavelength absorption of visible light, high intensity of photoluminescence and low density of defect recombination centers in present experiment.Finally, a SiN film was deposited on a-Si/a-Ge/(Si/Ge)3 multilayered structure as antireflection coating. And the effect of SiN thin films on the optical properties of a-Si/a-Ge/(Si/Ge)3 films were also discussed. After depositing SiN film on a-Si/a-Ge/(Si/Ge)3 films, multilayered films have better optical absorption and lower reflectance. The reflectance curve of SiN/a-Si/a-Ge/(Si/Ge)3 film is wave-like, and the positions of minimum is at the wavelength of 230nm,270nm,310nm,360nm and 570nm. These results demonstrate that the SiN thin film, deposited on a-Si/a-Ge/(Si/Ge)3 multilayered structure by RF magnetron reaction sputtering, has good reflected property not only in ultraviolet but also in visible light regions.