Oxide-related defects in quantum dot containing Si-rich silicon nitride films

Silicon-rich silicon nitride thin films were deposited by co-sputtering silicon and silicon nitride and annealed at high temperatures to form precipitates of silicon nanocrystals within the nitride matrix. This process was chosen to replicate the typical fabrication used for silicon nitride based quantum dots. Photoluminescence (PL) spectra were observed from the silicon nitride samples after a high temperature anneal and the PL peak shifted with increasing Si concentration. However, the time resolved PL spectra exhibited a fast decay in the nanosecond range, indicating that the PL does not originate from a radiative transition due to quantum confinement in the silicon nanocrystals. The chemical composition and the structural properties of the thin films were studied using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, and Raman spectroscopy. XPS and FTIR demonstrated that there was some oxygen incorporation in the as-deposited films, forming silicon oxynitride, which increased after high temperature annealing in N2 ambient. It is proposed that the PL originates from defect states related to the increased film oxidation after high temperature annealing and the shift in PL peak energies are due to transitions between the defect levels and the band edges of the nitride matrix.