Effect of plasma power strength on optical transitions in silicon-nitride films

We synthesized plasma-power-controlled silicon-nitride (PPCSN) films by using plasma-enhanced chemical vapor deposition (PECVD). We fixed the flow rates of SiH₄ (43 sccm) and N₂ (12.0 sccm) and varied the plasma power of the reactant gas in the range of 20 W to 60 W. Using photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), we investigated the origin of the luminescence from these films. As the plasma power has increased, we recognized that the PL peak position shifted toward higher energy and that the PL intensity became stronger. We also observed that all the PL spectra for the PPCSN films consisted of three transitions, which we denoted A, B, and I. Analyzing the Si 2p and N 1s XPS core-level spectra, we extracted several components of different chemical states. Using the chemical state analysis, we discuss the origin of the luminescence for each transition, A, B, and I. We noted that one component of the Si 2p chemical states indicated the extent of silicon quantum dots (QDs) and that the other one was closely associated with an increased PL intensity for transition A. We also concluded that transition I arose from the interfacial region between the Si QD and the silicon-nitride matrix. Transition B was related to some specific nanostructure, excluding Si QDs, of silicon nitride.