Abstract
The structural-phase transformations induced by air annealing of SiOx and SiOx < Er,F > films were studied by the combined use of infrared spectroscopy and ellipsometry. The films were prepared using vacuum evaporation of SiO powder and co-evaporation of SiO and ErF3 powders. The annealing took place at moderate temperatures (750 and 1000 °C). It was found that the micro- and macrostructure of the annealed films is similar to the structure of the Si–SiOx nanocomposites obtained by annealing SiOx in vacuum or inert atmosphere and subjected to post-annealing in oxidizing atmosphere. This proves that the phase separation in the non-stoichiometric SiOx films proceeds much faster than their oxidation. The results of the work point at a possibility to simplify the annealing technology by replacing the two-step annealing with one-step in the oxygen-containing environment while maintaining the positive effects. The differences in the structure of the nanocomposites obtained by annealing the SiOx and SiOx < Er,F > films are explained by the action of Er centers as the promoters for SiOx disproportionation, as well as the enhanced action of F on the processes of disorder-to-order transition and crystallization in amorphous silicon.
Highlights
Thin-film nanocomposites consisting of crystalline and amorphous Si nanoparticles embedded in silicon oxide layers have been actively studied during the last two decades as suitable materials for non-volatile memory devices, third generation of photovoltaic, and other applications
Under investigation of SiOx films annealed in vacuum [11], it was shown that the combination of infrared spectroscopy and ellipsometry can provide available information on the composition, homogeneity, and structural arrangement of the matrix as well as Si volume fraction and the morphology of Si nanoparticles
When solving the inverse task of ellipsometry (ITE) for every sample, we started with the simplest model, the Isotropic uniform transparent layer (IUTL) model, which is characterized by two parameters, the refractive index n and the thickness h
Summary
Thin-film nanocomposites consisting of crystalline and amorphous Si nanoparticles embedded in silicon oxide layers have been actively studied during the last two decades as suitable materials for non-volatile memory devices, third generation of photovoltaic, and other applications. One of the most widespread methods to produce these composites is the thermally stimulated phase separation in non-stoichiometric silicon oxide films (SiOx, x < 2). Such a process has been studied in detail [1]; the investigations were mainly concerned with the study of structuralphase transformations caused by thermal annealing of SiOx films in vacuum or in inert atmosphere. The presence of silicon nanoparticles (both amorphous and crystalline) in them has been confirmed by Raman spectroscopy [9, 10] The detailed data both on silicon inclusions and oxide matrix properties are necessary for subsequent performance optimization of these nanostructures. The purpose of this paper is to spread such an approach onto investigation of SiOx and SiOx < Er,F > films exposed to heat treatment in the air at the temperatures of 750 and 1000 °C
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