Study On Low Temperature Preparation And Optical Properties Of Crystalline Silicon Thin Films

The crystalline silicon thin films with advantages such as stable,high-efficiency, and cost-effective,it has become one of the most promising candidates for applications of photovoltaics.How to promote the crystallization rate and decrease annealing temperature has been one of the hottest scientific research areas at present. In this study,two kinds of crystalline silicon thin films,hydrogenated nanocrystalline silicon(nc-Si:H) and poly crystalline silicon have been studied.The deposition of hydrogenated nanocrystalline silicon(nc-Si:H) on float glass substrate at a relative high working pressure(100 Pa-500 Pa) is performed by using a conventional Radio Frequency Plasma Enhanced Chemical Vapor Deposition (RF-PECVD).The properties of nc-Si:H,such as crystallinity,optical band gap and photoluminescence have been studied in terms of process pressure,substrates temperature,and flow rate radio of H₂/SiH₄.It was found that at a relative high pressure(500 Pa) the film has good crystallinity and faster deposition rate.Structural characterizations of the films were performed by X-ray diffraction(XRD) and Field emission electron microscopy(FE-SEM).Optical characterization was performed by Raman spectroscopy and UV-VIS spectra and photoluminescence(PL) studies.The crystalline volume fraction and the crystallite size of the films estimated from the Raman spectra and XRD is found to vary from 5%to 68%and from 4.55 nm to 18.29 nm in diameter,respectively.And the Tauc's optical band gap is varied from 1.90 eV to 2.43 eV.And a novel deposition way of nickel film for crystallization of amorphous silicon film is introduced.Electroless nickel plating is a convenient and inexpensive way to deposit nickel without using the electric field or any complicated facilities.A 200 nm nickel film is deposited on the glass substrates and then a 200nm a-Si film is deposited on the nickel film.The bi-layer film is annealed at 500℃for several hours in the nitrogen atmosphere.The crystallized Si thin films were characterized by XRD, Raman spectroscopy,FE-SEM and energy dispersive spectroscopy(EDS).the Raman demonstrates that the a-Si has been crystallized and XRD shows that the crystalline of silicon is(111)-oriented.Furthermore,the lateral crystalline morphology shown in the FE-SEM photographs,manifests that the length of silicon grain is up to 5μm and the EDS reveals the nickel distribution in the MILC and MIC area.