engleski

Analysis of amorphous-nanocrystalline Si multilayer structures by GIXRD, XR, Raman spectroscopy and HRTEM

he multilayer structures containing Si thin films in the amorphous and crystalline forms are promising candidates for high efficiency thin film solar cells. Since the energy distribution of states for electrons depend upon the details of structural ordering like degree of crystallinity and individual crystal sizes it is possible to tailor in certain limits the opto-electrical properties. For practical use, it is of particular interest to find the proper deposition method for large scale production and proper diagnostic tools for estimation the structural properties in order to correlate them to the films properties and deposition condition. The representative set of samples was deposited by RF plasma enhanced chemical vapour deposition. The working gas was silane, diluted by hydrogen. By variation of silane to hydrogen ratio, different degree of structural ordering was obtained, going from pure amorphous to the high percentage of nano-crystalline phase. In particularly, high degree of crystal to amorphous fraction was obtained when silane contribution dropped towards few percent of working gas mixture. The samples were examined by Raman spectroscopy, high resolution transmission microscopy (HRTEM), grazing incidence diffraction and x-ray reflectometry (GIXRD & XR). The analysis of Raman spectra showed that the samples had the crystal fraction from 0 to some 70 vol%. The estimated size of crystals was between 2 and 20 nm, with broad size distribution. HRTEM, done on certain numbers of samples, confirmed the nano-meter size of crystals and showed that the crystal fraction increased with the thickness of the layer. The XR revealed variation of thickness and interface roughness of deposited layers, while GIXRD was performed at several angles very close to critical angle. In that way, it was possible to estimate crystalline fraction and average crystallite size in films with thickness from several 10 nm to several 100 nm ; the analysis of GIXRD data confirmed the non-uniform distribution of crystal fraction. The quantitative results of all of applied methods were mutually compared and result was discussed.

amorphous-nanocrystalline silicon; HRTEM; Raman; GIXRD

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