Light emission from nanocrystalline silicon clusters embedded in silicon dioxide: Role of the suboxide states Andriy Romanyuk a,Ã , Viktor Melnik b , Yaroslav Olikh b , Johannes Biskupek c , Ute Kaiser c , Martin Feneberg d , Klaus Thonke d , Peter Oelhafen a a Department of Physics, University of Basel, 4056 Basel, Switzerland b Institute of Semiconductor Physics, 03028 Kyiv, Ukraine c Electron Microscopy Group of Materials Science, University of Ulm, 89069 Ulm, Germany d Institute of Semiconductor Physics, University of Ulm, 89081 Ulm, Germany article info Article history: Received 23 March 2009 Received in revised form 21 June 2009 Accepted 28 July 2009 Available online 5 August 2009 PACS: 61.46.þw 73.20.r 78.67.n 79.60.Jv 81.07.b Keywords: Silicon nanoclusters Photoluminescence Cluster–matrix interface Ultrasound abstract Silicon clusters embedded in a silicon dioxide matrix were prepared by ultrasound-assisted implantation resulting in a modified concentration of suboxide states as revealed by high-resolution photoelectron spectroscopy. It is suggested that ultrasound treatment results in formation of different interface structure between silicon cluster and silicon dioxide matrix which is characterized by a distinctly reduced concentration of the suboxide states. It is observed that photoluminescence properties are strongly correlated with the concentration of the suboxide states thereby providing an evidence that besides a quantum confinement effect a closer look at the chemical composition of the nc- Si/SiO 2 system is important. & 2009 Elsevier B.V. All rights reserved. 1. Introduction Silicon is an indirect band gap semiconductor with the lowest point of the conduction gap shifted from the center of the Brillouin zone resulting in poor efficiency of light emission. Since the first observation of visible photoluminescence from porous silicon at room temperature reported in 1990 by Canham [1,2], properties of low dimensional silicon quantum structures have been a subject of extensive investigations motivated by the broad potential application of nanosized silicon in photonic and optoelectronic devices (for review see Refs. [3,4]). A large amount of work on the light emission from silicon-based nanostructures have been published so far with the majority devoted to the optical properties of nanocrystalline silicon (nc-Si) clusters embedded in the dielectric matrix of silicon dioxide. Some of the most fundamental questions related to the mechanism of light emission from silicon nanocrystals are still a matter of debate. On the one hand it is widely believed that the indirect gap limitation is surmounted by confinement of the exciton wave function in silicon crystallites with size below the size of the free exciton Bohr radius which is equal 4.3nm for bulk silicon [5,6]. In this case, the increase in the overlap of the electron and the hole wave functions substantially increases the prob- ability of a radiative recombination process resulting in higher luminescence efficiency. On the other hand, the light emission could also be due to the recombination via defect levels localized on the interface between nanocrystal and the amorphous silicon oxide matrix [7,8]. Several models of the interface-mediated light emission have been suggested including distortion of surface geometry [9], formation of pinning states [10,11], or assistance of a Si–O bond vibration at the nc-Si/SiO 2 interface [12]. The silicon nanocrystals can be produced by annealing silicon oxide supersaturated with excess silicon atoms, either introduced during growth by sputtering [13,14], chemical vapor deposition [15,16], laser ablation [17], or by ion implantation [18,19]. The latter method is routinely used in silicon integrated circuit technology and offers a number of advantages such as high controllability of dopant concentration and spatial distribution, as ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence 0022-2313/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jlumin.2009.07.021 Ã Corresponding author. Tel.: +4161 267 37 20; fax: +4161 267 37 84. E-mail address: andriy.romanyuk@unibas.ch (A. Romanyuk). Journal of Luminescence 130 (2010) 87–91