Analysis of silicon nanocrystals in silicon-rich SiO2 synthesized by CO2 laser annealing - art. no. 602020

Abstract

The localized synthesis of 4.2-5.6 nm-Si nanocrystals (nc-Si) in Si-rich SiO2 (SRSO) by CO, laser annealing at laser intensity of below ablation-threshold (6 kW/cm(2)) is demonstrated. Since the SRSO exhibits a high absorption coefficient of up to 0.102 cm(-1) at wavelength of 10.6 mu m, a direct-writing CO, laser annealing system with focusing spot 2 size of 0.2 mm(2) is used to locally anneal the SRSO and precipitate the nc-Si. A thermophysical model reveals that the surface temperature of SRSO ranging from 130 degrees C to 3350 degrees C is achieved by varying the laser power densities from 1.5 to 13.5 kW/cm(2). The CO2 laser-ablation-threshold power density is about 6 kW/cm(2). corresponding to the optimized annealing temperature 1285 degrees C at the ablation threshold. The CO2 laser annealing is capable of the precise control on power density and spot size, which benefits from the in-situ and localized annealing temperature control of SRSO film, and also prevents from the eternal damage of the other electronic devices nearby the annealing site. The nc-Si dependent photoluminescence (PL) were observed at 806 nm or longer, whereas the laser-ablation damaged SRSO film exhibits significant blue PL at 410 nm due to the oxygen-related structural defects. The refractive index of the laser-treated SRSO film is increasing from 1.57 to 2.31 as the laser intensity increases from 1.5 to 6.0 kW/cm(2) which is mainly attributed to the increasing density of nc-Si embedded in SRSO. High resolution transmission electron microscopy (HRTEM) analysis reveals that the average size of nc-Si embedded in SRSO film is about 5.3 nm, which correlates well with the theoretical prediction of a corresponding PL at 806 nm. The HRTEM estimated square density of the nc-Si in SRSO film under the laser intensity of 6 kW/cm(2) is about 10(18) cm(-3).