Nanocrystalline silicon films for photovoltaic and optoelectronic applications

The primary aim of this research project is to develop computational tools capable of assisting the design of a new nc-Si growth process with a Low Energy variant of a Plasma Enhanced Chemical Vapour Deposition (LEPECVD) reactor, addressed at the deposition of nc-Si films for both photovoltaic and optoelectronic applications. This objective is for many aspects really at the frontier of the today knowledge of multiphase materials, and for this reason requires the involvement of different theoretical and experimental tools and expertises. An LEPECVD reactor is actually in full use in one of the partner’s laboratories and has been already demonstrated to be a very powerful tool for high growth rate, high quality epitaxial silicon and silicon-germanium films. The modelling activities include Molecular dynamics (MD) and abinitio calculations applied to the simulation of the growth of nc-Si grains in a amorphous silicon (a- Si) matrix, to the evaluation of the best a-Si/ nc-Si ratio and the elastic/plastic effects consequent to the presence of nanocrystals of silicon in the a-Si matrix and to the presence of a grain boundary phase, which could be responsible of unwanted carrier recombination processes. The computational tools will be also used to evaluate the band offset vs microstructure and strain, in view of the fine-tuning of the optoelectronic properties. As the computer modelling could not be granted for a complete forecasting of the role of process parameters on the local nanostructural aspects and associated physical properties, additional theoretical studies on quantum confinement will be carried out. Such theoretical studies will be based on the results of systematic measurements of optoelectronic properties of nc-Si. The development of the computer modelling and of theoretical studies on quantum confinement will be paralleled, from the very early stage of the Project, by nc-Si growth experiments and by state of the art morphological, microstructural, compositional, electrical and optoelectronic characterization