Evolution of Si (and SiC) nanocrystal precipitation in SiC matrix Dengyuan Song ⁎ , Eun-Chel Cho, Young-Hyun Cho, Gavin Conibeer, Yidan Huang, Shujuan Huang, Martin A. Green ARC Photovoltaics Centre of Excellence, University of New South Wales, Sydney NSW 2052, Australia Received 20 October 2006; received in revised form 30 April 2007; accepted 19 June 2007 Available online 26 June 2007 Abstract Si 1-x C x films with varying ratio of carbon to silicon (C/Si) were fabricated by magnetron co-sputtering from a combined C and Si target. The composition in films was changed by adjusting the ratio of sputtered target's area between C and Si. Analysis of X-ray photoelectron spectroscopy for as-deposited films shows that C/Si atomic ratios of our films have ranges of 0.33–1.02. Thermal annealing of as-deposited films was carried out at various temperatures from 800 to 1100 °C in a conventional furnace. Fourier transform infrared spectra show a shift of Si–C stretching peak towards higher wavenumbers from ∼ 737 cm - 1 to ∼ 800 cm - 1 with increasing annealing temperature. From the results of Raman spectroscopy, X-ray diffraction and transmission electron microscopy, it was found that the dominant type of nanocrystals changes from Si to SiC in the films annealed at 1100 °C when the C/Si atomic ratio increases from 0.33 to 1.02. © 2007 Elsevier B.V. All rights reserved. Keywords: Sputtering; Silicon carbide; Annealing; Silicon nanocrystal; X-ray photoelectron spectroscopy; Raman spectroscopy; Infrared spectroscopy 1. Introduction Fabrication of silicon nanocrystals embedded in a dielectric matrix has attracted considerable interest in silicon optoelectron- ics [1–3] and in third-generation photovoltaics [4,5]. When silicon nanocrystals are made very small (b ∼ 7 nm in diameter), they behave as quantum dots (QDs) due to three-dimensional confinement of carriers [5]. Quantum confinement causes material's effective bandgap to increase. Carriers also can tunnel between dots to produce a quantum dot superlattice when these QDs are close enough together. For photovoltaic applications, such nanocrystal materials may allow the fabrication of higher bandgap solar cells that can be used as tandem cell elements on top of normal Si cells [4,5]. To date, considerable work has been done on the growth and characterization of Si nanocrystals embedded in oxide [6,7] and nitride [8,9] dielectric matrices. Compared to Si nanocrystals in oxide and nitride, recent modeling [10] shows that Si nanocrystals in SiC matrix are a promising material for all-silicon tandem solar cells because carrier transport should be easier due to a lower barrier height between neighboring nanocrystals and hence high tunneling probability. However, little has been reported on the experimental properties of Si nanocrystals embedded in SiC matrix [11]. In this work we have fabricated Si 1-x C x films with varying atomic ratio of the Si to C by using a magnetron co-sputtering from a combined Si and C target. Off-stoichiometric Si 1-x C x is of interest as a precursor to realize Si nanocrystals in SiC matrix, because it is thermodynamically metastable when the compo- sition fraction is with 0 b x b 0.5. Si nanocrystals are therefore able to precipitate during a post-deposition annealing. Raman spectroscopy and X-ray diffraction (XRD) measurement were used to investigate the evolution of Si and/or SiC nanocrystals in SiC matrix with increasing carbon content and annealing temperature. Furthermore, the samples were observed by high- resolution transmission electron microscopy (HRTEM), pro- viding direct evidence for the formation of nanocrystals in the films. On the basis of Raman, XRD and TEM results, we discuss three typical cases for annealed films with a low, intermediate and high carbon-to-silicon (C/Si) ratio, with the aim of analyzing the dependence of dominant type of nanocrystals (Si and/or SiC) on the film's composition and processing conditions. Available online at www.sciencedirect.com Thin Solid Films 516 (2008) 3824 – 3830 www.elsevier.com/locate/tsf ⁎ Corresponding author. Tel.: +61 2 9385 4454; fax: +61 2 9662 4240. E-mail address: s.dengy@unsw.edu.au (D. Song). 0040-6090/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2007.06.150