Light emitting mechanisms in Si-rich SiN_x films with different silicon nitride stoichiometry

Silicon-rich silicon nitride films with different stoichiometry were grown on the silicon substrate using the plasma-enhanced chemical vapor deposition. The excess silicon content in the films was monitored via varying the NH₃/SiH₄ gas flow ratio from 0.45 up to 1.0. High-temperature annealing was employed to produce the silicon nanocrystals (NCs) in the films and to enhance the photoluminescence in the range of 1.6–2.9 eV. Optical parameters of films were estimated by means of spectroscopic ellipsometry. Photoluminescence (PL) and its temperature dependences were studied as well. PL spectra were found to be complex due to the contribution of several radiative channels in the emission process. It was determined that their competition leads to the non-monotonous variation of total PL peak position with the increase of Si excess content. The analysis of PL temperature dependencies has revealed that the “blue–orange” emission is owing to the radiative host defects, whereas the “red” PL band is caused by the exciton recombination in Si NCs. The way to control emission is discussed.