Spectroscopic ellipsometry analyses of sputtered Si/SiO2 nanostructures

Abstract

A spectroscopic ellipsometry technique is used to attempt a quantitative analysis of thin Si/SiO2 nanocomposite films obtained by magnetron co-sputtering. The layers are first fabricated with varying values of deposition temperature and sputtered silicon area, before being annealed at different temperatures. Using an effective medium model, the ellipsometry tool allowed the estimate of the thickness and the volume fraction of silicon agglomerates or grains, in addition to the optical parameters of the layer through a tentative determination of the dielectric function of the Si nanostructures. The Si content obtained by the ellipsometry approach agrees with those previously determined by direct measurements. Besides the obvious increase of incorporated Si with the sputtered area of this material, we noticed a maximum excess of Si for a deposition temperature in the 400–500 °C range. In this respect, the peak position of the photoluminescence (PL) detected only in the annealed samples is found to be closely connected with the amount of excess Si, and in consequence, with the mean size of the thermally grown nanocrystallites. The systematic red shift of maximum PL with the rise of Si content, and implicitly with the increase of the particle size, regardless of the deposition conditions used for the fabrication of the original layer, is liable to allow conclusive argument as for the attribution of the PL in the 1.30–1.65 eV range to the quantum confinement effect. Besides the main contribution of the nanoparticle density, the quality of the Si/SiO2 interface, as examined by infrared absorption spectroscopy, appears determining for the PL efficiency, and is increasingly improved towards stoichiometric SiO2 when the annealing temperature is increased up to 1100 °C.

Energy Transfer from Silicon Nanocrystals to Er3+ Ions Embedded in Silicon Oxide Matrix

“…It has been established that, for our samples, Si nanocrystals have been formed when the samples were annealed at 950°C (see Figure 3 (b) in section 3.1 above). The emission peaked at ~800nm can only be observed when Si nanocrystals are present in the samples and is attributed to the exciton recombinations in Si nanocrystals (Bulutay, 2007;Charvet et al, 1999;Kik & Polman, 2001;Seino et al, 2009;Silalahi et al, 2009Wilkinson & Elliman, 2003). The increase of the emission intensity at the higher annealing temperature (in our case, 1050°C compared to 950°C) has also been reported and attributed to the better crystallization of Si nanocrystals (Kahler & Hofmeister, 2002;Kapaklis et al, 2005).…”

Effect of annealing and Nd concentration on the photoluminescence of Nd3+ ions coupled with silicon nanoparticles

“…The attenuation of the TO 4 -LO 4 pair modes with the annealing temperature indicates a reduction in disorder. 19 Besides, one can observe a progressive shift to higher wavenumbers of the TO 3 and LO 3 bands toward the stoichiometric positions of amorphous SiO 2 at 1076 cm −1 and 1256 cm −1 , respectively, while the annealing temperature was increased. It is explained by the condensation and agglomeration of the Si excess resulting in the formation of Si-np.…”

“…It is explained by the condensation and agglomeration of the Si excess resulting in the formation of Si-np. 20,21 In the same time, the increase in the LO 3 bands intensity is related to the increase in the number of Si-O-Si bonds at the SiO x / Si-np interface, 19,21 i.e., the increase in the density of Si-np. 22 Figure 2 shows the evolution of the FTIR spectra of the samples annealed at 1100°C as a function of the Nd concentration.…”

Low-loss rib waveguides containing Si nanocrystals embedded in SiO2

“…The values obtained here for the refractive index at 632 nm are about 7% higher than those obtained by Charvet et al for similar Si excess in sputtered samples. 22 This difference can be accounted for by the higher compactness of our samples.…”