The Properties Of Photoluminescence Of LiNbO₃/SiO₂/Si Multilayer Films

LiNbO₃/Si and LiNbO₃/SiO₂/Si films were fabricated by radio-frequency (RF) magnetron sputtering technique. The microstructure of the films were characterized by X-ray diffraction (XRD), X-ray small angle diffraction technique, inductively coupled plasma mass spectrum (ICP-MS) and Fourier transform infrared absorption spectrum(FT-IR). The effects of sputtering parameters such as substrate temperature, working pressure, sputtering gas Ar/O₂ flow rate, sputtering time, and SiO₂ transition layer on the photoluminescence (PL) properties of the LiNbO₃ multilayer films were studied. The mechanism of photoluminescence properties of the LiNbO₃ multilayer films was discussed.The optimal RF magnetron sputtering parameters of the high-quality c-axis orientation LiNbO₃ thin films were as follows: substrate temperature of 600℃, sputtering power of 50w, working pressure of 0.8 Pa, Ar/O₂ flow rate of 6/4 and sputtering time for 5h.PL spectra showed that blue visible emission can be observed in the LiNbO₃ multilayer films. Emission peaks situated at 439nm, 450nm and 470nm, in which the 470nm emission peak has the strongest intensity, the 439nm and 450nm emission intensities are weaker.Comparison the effect of different growth conditions and SiO₂ transition layer on the photoluminescence properties of the LiNbO₃ multilayer films. Substrate temperature is a decisive factor, so we should choose the higher substrate temperature; working pressure has the best value, and has impact on the changes of intensity; sputtering gas Ar/O₂ flow rate has minor influence to the photoluminescence properties; sputtering time has the contribution to the peak strong increase. In addition, we firstly achieved that the thickness of SiO₂ layer has no effect in the position of emission peaks. But the SiO₂ transition layer can remarkably increase the surface roughness between the LiNbO₃ thin film and Si substrate, enhances the area of contact interface, causes the radiative recombination enhancement, and results in the photoemission intensity enhances.The LiNbO₃ multilayer films photoluminescence mechanism was discussed. Eliminated the luminescence mechanism of neutral oxygen vacancy defect (O3≡Si―Si≡O3) in SiO₂ layers.According to the above analysis, we may infer that LiNbO₃ has good photorefractive effect (PRE), and results in the strong space charge field. The strong space charge field in the LiNbO₃ films can induce large lattice distortion at the surfaces of the SiO₂ layers. The photoexcited carriers in the coated film could be trapped by the distorted lattice, to form so-called self-trapped excitons. Radiative recombination of the self-trapped excitons leads to light emission.