How thick SiO2 cap layer is needed to achieve strong visible photoluminescence from SiO2-buffered SiNx films?

The effect of a SiO2 nanolayer and annealing temperature on the UV/visible room-temperature photoluminescence (PL) from SiNx films synthesized by rf magnetron sputtering is studied. The PL intensity can be maximized when the SiO2 layer is 5-10 nm thick at 800 °C annealing temperature and only 2 nm at 1000 °C. A composition-structure-property analysis reveals that the PL intensity is directly related to both the surface chemical states and the content of the Si-O and Si-N bonds in the SiNx films. These results are relevant for the development of advanced optoelectronic and photonic emitters and sensors.