Structural and optical properties of silicon quantum dots in silicon nitride grown in situ by PECVD using different gas precursors

A low temperature in situ approach for growing silicon nanostructures in silicon nitride is investigated, as a powerful method of implementing third generation photovoltaic concepts within classical thin film silicon solar cell architectures on low cost substrates. Evidence of spontaneous aggregation of silicon quantum dots in silicon nitride films deposited by plasma enhanced chemical vapour deposition (PECVD) at low temperature (300 °C) is reported. Two different types of samples are studied, grown using two gas mixtures, composed of silane and nitrogen with and without ammonia. The film microstructure is analysed through Raman spectroscopy. Visible photoluminescence (PL) is observed in all cases, and tuning of PL emission is demonstrated by adjusting the gas flow rates. As an effect of the extra hydrogen available through the dissociation of NH3, much stronger PL is observed on samples grown with ammonia. Similar optical absorption spectra are found for the two types of samples, with the rising edge dominated by the absorption in Si nanoclusters.