Correlating Raman-spectroscopy and high-resolution transmission-electron-microscopy studies of amorphous/nanocrystalline multilayered silicon thin films

The nanostructure of multilayered silicon thin films was studied using Raman spectroscopy (RS) and high-resolution transmission electron microscopy (HRTEM). Since the properties of nanocristalline silicon (nc-Si) layer depend on the size of the nanocrystals, an accurate determination of the crystallite sizes and the crystalline fraction for nc-Si is of primary importance. The average sizes of the nanocrystals estimated by RS, assuming bi-modal distribution of crystal sizes, were close to 2 nm and above 5-20 nm. HRTEM confirmed the existence of nanocrystals with a mean square value of around 2 nm and certain number of larger nanocrystals, embedded in amorphous matrix. The correlation between the results obtained by these two techniques is discussed. The optical properties of measured samples corresponded to amorphous-crystalline mixture with indication of confinement effects related to 2 nm nanocrystals.