White photoluminescence from SiNx films prepared by plasma enhanced chemical vapor deposition

Intense visible blue to red emissions were obtained from SiNx thin films prepared by plasma enhanced chemical vapor deposition (PECVD) using SiH4 and NH3 as the source gases. A continuous blue shift of the photoluminescence (PL) peak from 660nm to 440nm was observed by increasing the NH3 flow rate from 20 to 150sccm, while the flow rate of N2 diluted 2% SiH4 was fixed at 650sccm. This controllable PL was attributed to the quantum confinement effect of Si quantum dots (QDs) which were formed during the deposition process and embedded in the SiNx films. White photoluminescence with multiple emission peaks was achieved for potential solid state lighting applications from multi-layered SiNx films by changing the SiH4/NH3 ratio during the deposition process. This was attributed to a combination of Si quantum dots with different sizes within the different layers. Surface texturing of the thin film samples was conducted by potassium hydroxide (0.56%) etching the (100) Si substrate for 3~40 min at 80°C before deposition. The reflectivity of the etched samples decreased with increasing etch time due to increased surface roughness. The extraction efficiency of light emission from the textured SiNx thin films was significantly improved, owing to a depression of the internal reflection and interference effects. In addition, the elimination of the multiple emission peaks by surface texturing significantly affected the color coordinates of the output spectrum.

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