Characterization of Ge nanocrystals embedded in SiO₂by Raman spectroscopy

Abstract

Ge nanocrystals formed in a SiO 2 matrix by ion implantation were studied by Raman spectroscopy. It is shown that Raman analysis based on the phonon confinement model yields a successful explanation of the peculiar characteristics resulting from the nanocrystals. A broadening and a shift in the Raman peak are expected to result from the reduced size of the crystals. Asymmetry in the peak is attributed to the variations in the size of the nanocrystals. These effects were observed experimentally for the Ge nanocrystals prepared by ion implantation and explained theoretically by incorporating the effect of size and size distribution into the theoretical description of the Raman shift. A comparison with the transmission electron microscopy images indicated that this analysis could be used to estimate the structural properties of nanocrystals embedded in a host matrix. The evolution of nanocrystal formation with annealing temperature, i.e. the size growth, was monitored by Raman spectrometry for several samples and the corresponding nanocrystal sizes were estimated using the phonon confinement model.

Structural properties of Ge nanocrystals embedded in sapphire

“…A similar, though smaller, blue shift of Raman spectra of silicaembedded Ge nanocrystals is frequently observed and is attributed to matrix-induced compressive stress on embedded nanocrystals. [15][16][17][18][19][20] i. Quantitative Stress Analysis…”

Raman and TEM studies of Ge nanocrystal formation in SiOx:Ge/SiOx multilayers

“…Among many properties of interest, structural information revealing crystal structure, nanocrystal shape, type and density defects is fundamental because they determine almost all other properties of the nanocrystals. Structural information can be obtained by several analytical techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman scattering spectroscopy to name a few [2,3]. Ge nanocrystals have been obtained by ion beam synthesis in SiO 2 and post growth annealing [4,5].…”

Evolution of SiO2/Ge/HfO2(Ge) multilayer structure during high temperature annealing

“…A presence of such a shoulder is then an indication of nano-sized structure. In our earlier publication, we showed that the size of Ge nanocrystals can be estimated from the asymmetric Ge peak [17]. The annealing temperature of 700°C is lower end of the temperature range in which Ge crystallization occurs.…”