Modification of Light Emission in Si-Rich Silicon Nitride Films Versus Stoichiometry and Excitation Light Energy

Si-rich SiN_x films with different stoichiometry were grown on Si substrate by plasma-enhanced chemical vapor deposition. The Si content was varied by changing the NH₃/SiH₄ gas flow ratio from 0.45 up to 1.0. Conventional furnace annealing at 1100°C for 30 min was applied to produce the Si quantum dots (QDs) in the SiN_x films. Spectroscopic ellipsometry was used to determine the refractive index of the SiN_x films that allowed estimating the film's stoichiometry. Fourier transform infrared spectroscopy has been also used to confirm the stoichiometry and microstructure. Photoluminescence (PL) spectra of Si-rich SiN_x films are complex. A non-monotonous variation of the different PL peaks versus Si excess contents testifies to the competition of different radiative channels. The analysis of PL spectra, measured at the different excitation light energies and variable temperatures, has revealed that the PL bands with the peaks within the range 2.1–3.0 eV are related to the carrier recombination via radiative native defects in the SiN_x host. Simultaneously, the PL bands with the peaks at 1.5–2.0 eV are caused by the exciton recombination in the Si QDs of different sizes. The way to control the SiN_x emission is discussed.