Optical Study of SiO 2 /nanocrystalline-Si Multilayers Using Ellipsometry Kang-Joo Lee 1 , Tae-Dong Kang 1 , Hosun Lee 1,a , Seung Hui Hong 1 , Suk-Ho Choi 1 , Kyung Joong Kim 2 , and Dae Won Moon 2 1 Department of Physics and Institute of Natural Sciences, Kyung Hee University, Suwon 449- 701, Korea 2 Nano Surface Group, Korea Research Institute of Standards and Science, P.O.Box 102, Yusong, Taejon 305-600, Korea ABSTRACT Using variable-angle spectroscopic ellipsometry, we measure the pseudo-dielectric functions of as-deposited and annealed SiO 2 /SiO x multilayers (MLs). The SiO 2 (2nm)/SiO x (2nm) MLs have been prepared under various deposition temperature by ion beam sputtering. The annealing at temperatures ≥ 1100°C leads to the formation of Si nanocrystals (nc-Si) in the SiO x layer of MLs. Transmission electron microscopy images clearly demonstrate the existence of nc-Si. We assume a Tauc-Lorentzian lineshape for the dielectric function of nc-Si, and use an effective medium approximation for SiO 2 /nc-Si MLs as a mixture of nc-Si and SiO 2 . We successfully estimate the dielectric function of nc-Si and its volume fraction. We find that the volume fraction of nc-Si decreases after annealing, with increasing x in as-deposited SiO x layer. This result is compared to expected nc-Si volume fraction, which was estimated from stoichiometry of SiO x . a) Corresponding author: hlee@khu.ac.kr INTRODUCTION In order to realize light-emitting-diode using silicon-based materials, intensive investigations on nanocrystalline silicon (nc-Si) have been carried out. Due to the confinement of electron and hole carriers in nano-scale volumes, we expect enhanced luminescence efficiency due to increasing recombination rate of carriers as well as the visible luminescence arising from quantum confinement effect [1]. Notably, superlattices composed of alternating nc-Si and SiO 2 layers have been given much attention due to a large volume fraction of nc-Si and the controllability of the size and density of nc-Si crystallites [2-3]. One promising method of nc-Si/SiO 2 MLs relies on the growth of SiO x /SiO 2 multilayers (MLs) and subsequent heat treatment [4]. We used ion beam sputtering deposition (IBSD) method to grow SiO x /SiO 2 MLs. IBSD has the advantage of low operational pressure of the ion sources and the precise control of the ion beam parameters, compared to plasma-based rf sputtering techniques. Defect densities are relatively low because a neutralized ion beam is used for sputtering and a substrate is not immersed in the plasma [5,6]. In order to optimize nc-Si/SiO 2 MLs for optoelectronic devices, we need various structural and optical characterization methods [2,3,5,7]. Using spectroscopic ellipsmetry, we can characterize the structural and optical properties at the same time. In detail, we can estimate the thickness of the nc-Si and SiO 2 layers and the volume fraction of nc-Si, as well as the dielectric function of nc-Si. Recently, several researchers successfully adopted Tauc-Lorentz (TL) model for the dielectric function of nc-Si of the diameters of 1 to 3 nm [8,9]. Mat. Res. Soc. Symp. Proc. Vol. 817 © 2004 Materials Research Society L4.4.1