Evolution of photoluminescence from Si nanocrystals embedded in a SiO 2 matrix prepared by reactive pulsed laser deposit
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Photoluminescence (PL) properties of SiOx thin films deposited by pulsed laser ablation of Si in a reactive oxygen ambient and annealed in a nitrogen atmosphere were studied at room temperature. Raman spectroscopy, Fourier transform infrared spectroscopy, and optical transmission measurements were used to characterize the deposited films before and after annealing and complement the PL studies. Strong PL due to quantum confinement was observed at room temperature from Si nanocrystals with an average diameter of approximately 5 nm at 325-nm light excitation. An apparent dependence of PL on the oxygen pressure for film deposition was observed. A detailed analysis of the effects of the annealing temperature revealed a significant PL evolution in luminescence intensity, spectrum profile, peak position, and spectrum range with the annealing temperature ranging from 300 to 1200 C. Structural variations induced by thermal annealing of the films deposited at different oxygen pressures were also discussed on the basis of their correlation with the PL evolution. I. INTRODUCTION
Since the discovery of efficient room temperature photoluminescence (PL) from porous Si by Canham,1 and from silicon ultrafine particles by Takagi et al.,2 Si nanostructures have attracted much attention due to their light emission in the near-infrared to red regions at room temperature and potential applications in Si-based optoelectronic and optical devices. Among various Si nanostructures, Si nanocrystals embedded in a SiO2 matrix (Si-NCs/SiO2) are considered as one of the most promising Si-based, light-emitting materials because of their appreciable and stable light emission, as well as their robust structure compared with porous Si prepared by anodization. In addition, optoelectronics based on SiNCs/SiO2 seems compatible with the current Si-based microelectronics technology, and effective integration of Si-NCs-based optoelectronic devices is expected. Si-NCs/ SiO2 can be fabricated by direct introduction of silicon into silicon dioxide using Si ion implantation,3–5 or thermal annealing of amorphous silicon suboxides (a-SiOx) films deposited by chemical vapor deposition,6–8 pulsed laser deposition (PLD),9–11 sputtering,12,13 and thermal evaporation of SiO powder.14,15 Solid SiOx is thermodynamically unstable, and the decomposition of SiOx takes place when it is annealed at high temperatures, leading to the precipitation of Si and the formation of Si-NCs/ SiO2.6,12,16 This chemical disproportionation reaction a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0279 J. Mater. Res., Vol. 24, No. 7, Jul 2009
accompanied by diffusion processes in Si-rich oxide films is probably one of the simplest methods to obtain light-emitting Si nanostructures. The crystal size and thereby the emitted light are directly controlled by the excess of Si quantity in the initial a-SiOx films, which may be another reason for Si-NCs/SiO2 to be promising for potential application in Si-based optoelectronics. The luminescence fro
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