Artículos de revistas
From amorphous to crystalline silicon nanoclusters: structural effects on exciton properties
Date
2011-12Registration in:
Journal of Physics: Condensed Matter,Bristol : Institute of Physics - IOP, v. 23, n. 50, p. 505302-1-505302-10, Dec. 2011
0953-8984
10.1088/0953-8984/23/50/505302
Author
Borrero-González, L. J.
Nunes, Luiz Antonio de Oliveira
Guimarães, Francisco Eduardo Gontijo
Wojcik, J.
Mascher, P.
Gennaro, A. M.
Tirado, M.
Comedi, D.
Institutions
Abstract
Synchrotron x-ray absorption spectroscopy (XAS) and electron spin resonance (ESR) experiments were performed to determine, in combination with Raman spectroscopy and x-ray diffraction (XRD) data from previous reports, the structure and paramagnetic defect status of Si-nanoclusters (ncls) at various intermediate formation stages in Si-rich Si oxide films having different Si concentrations (y = 0.36-0.42 in SiyO1-y), fabricated by electron cyclotron resonance plasma-enhanced chemical vapor deposition and isochronally (2 h) annealed at various temperatures (Ta = 900-1100 °C) under either Ar or (Ar + 5%H2) atmospheres. The corresponding emission properties were studied by stationary and time dependent photoluminescence (PL) spectroscopy in correlation with the structural and defect properties. To explain the experimental data, we propose crystallization by nucleation within already existing amorphous Si-ncls as the mechanism for the formation of the Si nanocrystals in the oxide matrix. The cluster-size dependent partial crystallization of Si-ncls at intermediate Ta can be qualitatively understood in terms of a 'crystalline core-amorphous shell' Si-ncl model. The amorphous shell, which is invisible in most diffraction and electron microscopy experiments, is found to have an important impact on light emission. As the crystalline core grows at the expense of a thinning amorphous shell with increasing Ta, the PL undergoes a transition from a regime dominated by disorder-induced effects to a situation where quantum confinement of excitons prevails.