Control of and Mechanisms for Room Temperature Visible light Emission from Silicon Nanostructures in SiO 2 formed by Si
- PDF / 786,881 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 40 Downloads / 172 Views
Department of Electronic and Electrical Engineering University of Surrey, Guildford, Surrey, GU2 5XH, UK
ABSTRACT
Implantation of Si+ ions into thermal oxides grown on silicon has been used to synthesise a two phase structure consisting of Si nanocrystals in a Si0 2 matrix. Various processing conditions have been used in order to modify the size and population distributions of the Si inclusions. Photoluminescence spectra have been recorded from samples annealed in nitrogen, forming gas and oxygen. Both red and blue shifts of the luminescence peaks have been observed. It is concluded that the photoluminescence is a consequence of the effects of quantum confinement but is also dependent on the presence of irradiation-induced defects or Si/SiO 2 interface states.
Introduction Following the report by Canham [1] of visible photoluminescence at room temperature from porous silicon, there has been worldwide activity both to identify the mechanisms of light emission and, also, to explore the utility of using these structures as visible light sources.
Several distinctly different mechanisms [2] have been proposed for the observed luminescence but currently there is a general consensus that the phenomena is associated with quantum confinement effects in the oxidized silicon nanostructures. Mechanisms involving SiHx [3] or siloxenes [4] have recently been ruled out following experimental investigations. Theoretical studies [5,6] have shown that quantum confinement in small Si or Ge nanostructures can modify exciton energies giving rise to visible photoluminescence which is strongly
dependent on the dimensions of the structures. Calculations suggest that spherical Si quantum dots of diameter 30 A will have a luminescence peak energy of =1.5 eV [5]. Recent detailed experimental investigations of porous Si and oxidized Si nanostructures by Schupper et al. [7]
confirm that the visible luminescence is associated with particles, but not wire-like structures, with dimensions significantly smaller than previously proposed. They find that luminescence peaking at 2 eV is associated with particles typically smaller than 13 A and is relatively insensitive to the method of preparation of the porous Si. However the details of the
mechanisms responsible for visible photoluminescence are still unknown and the role of defects and radiative traps associated with the Si/SiO 2 interface is still to be determined and quantified
[8].
Quantum confinement as the prerequisite for visible light emission has been demonstrated in Si nanostructures formed by a variety of other methods [2] including CVD, microwave plasma deposition and ion beam synthesis. Recently Atwater et al. [8], Shimizu-Iwayama et al. [9,10] and Komoda et al. [II] have reported the synthesis of Si microcrystals by the implantation of Si+ ions into thermal Si0 2 or vitreous silica specimens and observed visible photoluminescence (PL) which exhibits many of the features previously observed in porous silicon. An important 163 Mat. Res. Soc. Symp. Proc. Vol. 358 01995 Materials
Data Loading...
