Generation of optically active states in a-SiNx by thermal treatment

Amorphous silicon nitride (a-SiNx) films were deposited using plasma-enhanced chemical-vapor deposition (PECVD) and subsequently, thermal annealing processes were performed at 700–1000 °C in the ultra-high vacuum (UHV) condition. A strong photoluminescence (PL) peak induced by luminescent defect centers was observed at 710 nm for the as-deposited sample. When the sample was annealed at 700–1000 °C, the PL peak intensity became about 3–12 times stronger with no shift of the PL peak. To investigate the origin of the change in PL peak intensity after the thermal annealing, Si 2p and N 1s core-level spectra were systematically analyzed by high-resolution photoemission spectroscopy (HRPES) using synchrotron radiation. In particular, N 1s spectra were decomposed with three characteristic nitrogen-bonding states. It is revealed that the nitrogen bonding state with N–Si and NSi2 configurations (denoted as N3) contributes mainly to the change in PL peak intensity. We note that luminescent nitrogen related defect centers such as N4+ and N2° are localized in the state N3. Detailed analysis of the experimental results shows that the state N3 is located in the interface bounded by the region of the nano-sized stoichiometric silicon nitride Si3N4 (denoted as N1) and is considerably influenced by the thermal annealing, which is an appropriate process to cause strong photoluminescence of the related samples as mentioned above.