Morphology of Si nanocrystallites embedded in SiO 2 matrix
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V. Iancu Department of Physics, University “Politehnica” of Bucharest, Bucharest R-060042, Romania
M-G. Blanchin Université Claude Bernard Lyon 1, Laboratoire de Physique de la Matie`re Condense´e et Nanostructures (PMCN), Centre National de la Recherche Scientifique (CNRS) UMR 5586, 69622 Villeurbanne Cedex, F-69000 France (Received 7 April 2008; accepted 1 August 2008)
The nanostructure of Six(SiO2)1–x films deposited on quartz substrate, where x varies from 0 to 1, was determined by high-resolution transmission electron microscopy in the sample regions with x ≈ 0.1, 0.2, 0.5, and 0.75. In the Si0.5(SiO2)0.5 region, the formation of a Si nanocrystallite network was established. At high concentrations of Si nanocrystallites, nanotwins and stacking faults occurred in the crystallites. Large Si crystallites appeared at x 艌 0.5 in the quartz substrate under the interface, while the film presented nanopores over the interface. The mechanisms for the formation of the nanocrystallites were discussed and correlated with the film properties. I. INTRODUCTION
The silicon nanocrystallite (nc-Si) structures embedded in amorphous silicon dioxide (a-SiO2) films are interesting for different applications in nano- and optoelectronics, such as floating gate memory devices,1 or floating gate metal-oxide-semiconductor field-effect transistor (MOSFET) light sources.2 They are generally obtained starting from a Si-rich silicon oxide by annealing at high temperature in an inert atmosphere. Such films were prepared by different methods: cosputtering of Si and SiO2,3–6 plasma enhanced chemical vapor deposition,7,8 pulse laser deposition,9–11 electron beam coevaporation of Si and SiO2,12,13 Si ion implantation,14–16 etc. The correlation between the structural features and the physical properties of these systems is a key point to develop their potential applications. Several investigations of Si–SiO2 thick films, focused on the electrical transport17,18 and on the structural aspects,19 were already published by us. The purpose of this paper is to present a cross-section transmission electron microscopy (XTEM) study of the Si nanocrystallite embedded in the SiO2 matrix, revealing some new features related to their formation mechanism. These features also control the physical properties of the system. The experimental details are listed in Sec. II. Section III presents the obtained results and Sec. IV
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0358 2990
http://journals.cambridge.org
J. Mater. Res., Vol. 23, No. 11, Nov 2008 Downloaded: 16 Mar 2015
discusses them. The last section summarizes the conclusions. II. EXPERIMENTAL
Amorphous SiOy thick films were prepared by cosputtering of Si and SiO2 on a quartz slide (126 mm × 11 mm), for 12 h.5,18,19 Two targets located at 50 mm below the slide were used. The sputtering was performed in a pure argon atmosphere (99.999%), using a radiofrequency (rf) voltage of 110 V (forward power 180 W). The obtained films have a thickness between 5 and
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