Correlation between matrix structural order and compressive stress exerted on silicon nanocrystals embedded in silicon-r
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NANO EXPRESS
Open Access
Correlation between matrix structural order and compressive stress exerted on silicon nanocrystals embedded in silicon-rich silicon oxide Grzegorz Zatryb1, Artur Podhorodecki1*, Jan Misiewicz1, Julien Cardin2 and Fabrice Gourbilleau2
Abstract Silicon nanocrystals embedded in a silicon oxide matrix were deposited by radio frequency reactive magnetron sputtering. By means of Raman spectroscopy, we have found that a compressive stress is exerted on the silicon nanocrystal cores. The stress varies as a function of silicon concentration in the silicon-rich silicon oxide layers varies, which can be attributed to changes of nanocrystal environment. By conducting the Fourier transform infrared absorption experiments, we have correlated the stresses exerted on the nanocrystal core to the degree of matrix structural order. Keywords: Silicon, Nanocrystals, Stress, Raman, Phonon, Confinement, Order, Disorder, Matrix PACS: 78.67.Bf, 78.67.Pt, 73.63.Bd, 78.47.D, 74.25.Nd
Background Silicon nanocrystals (Si-NCs) embedded in a silicon-rich silicon oxide (SRSO) have been extensively studied due to their promising applications in the third generation tandem solar cells [1], light-emitting diodes [2], or silicon-based lasers [3]. These SRSO structures may be successfully deposited by magnetron sputtering technique. After deposition, during annealing in a N2 atmosphere and 1,100°C temperature, the excess silicon in SRSO layer precipitates to form Si nanocrystals in nearly stoichiometric silicon dioxide matrix. The structural quality of the matrix surrounding Si-NCs is very important since it influences the optical properties of Si-NCs [4]. For example, it has been shown that various defects present in the matrix may quench the emission originated from Si-NCs due to non-radiative recombination [5]. This is a serious problem from the point of view of applications, especially in the case of light-emitting devices. Besides the optical properties, due to differences in Si-NCs and SiO2 crystal structure, the matrix structural ordering may affect also the Si-NCs crystallinity and shape. It has been shown by first-principles calculations
that the surrounding matrix always produces a strain on the nanocrystals, especially at the Si-NCs/SiO2 interface. According to theory, the amount of stress exerted on the nanocrystal is connected to the Si-NCs size [6] as well as to the number of oxygen per interface silicon [7]. These structural parameters can be controlled during deposition process by varying the excess silicon concentration in the SRSO matrix [8]. The structural properties of the Si-NCs may be then experimentally examined by means of the Raman spectroscopy, since the Si-Si bonding is Raman active. On the other hand, Si-O-Si bonds are active in the infrared (IR) region and therefore the matrix properties can be examined by means of the Fourier transform IR (FTIR) spectroscopy. In this work, we investigate the correlation between short-range structural order of the matrix and stress exerted on the Si-NCs by mea
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