Structure and photoluminescence features of nanocrystalline Si/SiO2 films produced by plasma chemical vapor deposition and post-treatment

Abstract

Experimental results of the visible photoluminescence (PL) from nanocrystalline Si (nc-Si) embedded in a SiO2 matrix, prepared by plasma Chemical vapor deposition and a subsequent post-treatment, are reported here. Scanning electron microscopy, transmission electron microscopy, x-ray diffraction, and Fourier transform infrared are used to characterize the morphology, crystallite size, and the composition and structure of nc-Si/SiO2 films. The visible PL can be finely tuned from 1.3 to 1.75 eV by changing annealing time and temperature. The effect of high temperature (870 °C) forming gas (FG) annealing on the visible PL can be divided into three stages. In the first stage, the visible PL blueshifts from 1.3 to 1.55 eV, and the PL intensity increases. In the second stage, the peak energy shows a small shift, and the PL intensity continues increasing. In the last stage, the peak energy blueshifts to ∼1.75 eV, but the PL intensity decreases. The visible PL shows a maximum intensity around 1.5±0.05 eV. For a PL obtained after a high temperature anneal, a subsequent low temperature FG annealing (400 °C) will lead to a redshift of peak energy and an increase in PL intensity. In particular, for a PL around 1.75 eV, a kinetic oscillation of the spectral shift and the PL intensity has been observed upon this annealing. Detailed analysis indicates that the most probable candidates for the visible PL are two oxygen thermal donor-like defect states (TDs) (Si-NL8 and Si-NL10) generated during annealing. The effect of annealing temperature and time on the spectral change and the kinetic oscillation of the spectral change can be explained by the formation and decay kinetics of these two oxygen TDs-like defect states. On the one hand, these experimental results verified the Si–O bond related origin for the visible PL in this system; on the other hand, they also pointed out that apart from the common features of Si–O related visible PL, the detailed configuration and composition of this PL center by different synthesis methods may be different and possess some features of their own.