Annealing effects on the photoluminescence of amorphous silicon-nitride films

Amorphous silicon-nitride films were deposited at low temperature (350 °C) and with high deposition rates (220 - 280 Å/min) by using plasma-enhanced chemical-vapor deposition (PECVD). The optical and the structural properties of these films have been characterized by using photoluminescence (PL) and atomic force microscopy (AFM). Five broad emission peaks, one each at 3.1, 2.4, 2.15, 1.9, and 1.75 eV, were observed in the PL spectra by adjusting the flow rate of the nitrogen gas. As the nitrogen gas flow was increased, the wavelength of the emitted light shifted from blue to red in the PL spectra. After the films were annealed at 700 - 1000 °C for 10 min in ultra-high vacuum (UHV) condition, the PL intensity became 4-10 times stronger while the positions of the PL peaks were not changed. These experimental results show that the PL of amorphous silicon nitride films is closely related to the formation of optically active defect states. According to this interpretation, we will explain the PL enhancement after the thermal annealing process.