Photoluminescence comparison of SRO-LPCVD films deposited on quartz, polysilicon and silicon substrates

Abstract

In the present work, photoluminescence spectra of silicon-rich oxide monolayers (SRO10 and SRO25) and bilayers (SRO25/10, SRO10/25) films deposited on quartz, polysilicon on quartz and silicon substrates are compared. Silicon-rich oxide films were deposited using Low Pressure Chemical Vapor Deposition (LPCVD) technique. The films were characterized by Ellipsometry, Fourier Transform Infrared Spectroscopy, Secondary Ion Mass Spectrometry, Optical Transmittance, Photoluminescence, Scanning Electron Microscope, and High-Resolution Transmission Electron Microscopy. The results show that the bilayer films, deposited on polysilicon film on quartz have the stronger photoluminescence, which is indicative that there are different types of defects, Silicon nanocrystals, Silicon nanoparticles, and amorphous silicon nanoparticles that improve the Photoluminescence response. Also, it was observed constructive interferences in the transmittance a spectrum of silicon-rich oxide films/polysilicon films on quartz, due to that their refractive indices are different and they are together. This, when a beam of light crosses the interface between materials with different refraction indexes, its direction of propagation is altered, and the bigger is the difference of its refractive indexes, the greater will be the beam refraction. In all materials known this phenomenon is called as positive refraction. The photoluminescence is related to silicon dioxide defects such as weak oxygen bonds, neutral oxygen vacancy, non-bridging oxygen hole centers, or positively charged oxygen vacancies. Moreover, it is a combined effect where the bandgap energy acquires some direct bandgap properties due to quantum confinement, both effects (defects and quantum confinement) are important to increase the photoluminescence intensity. The average diameters of Silicon nanocrystals were estimated from the band gap energy and also by High-Resolution Transmission Electron Microscopy obtaining an average diameter of 3.8 ± 0.08 nm. Comparative analysis of optical and structural properties was performed on all samples.