Investigation of photoluminescence of silicon rich nitrides multilayer thin films

Abstract

Silicon is a very important material in the electronics industry. However, due to its indirect bandgap characteristic, it is an inefficient light emitter. Intensive research had been conducted to come up with different types of silicon-based materials that are suitable for optoelectronic applications. Examples include amorphous silicon nitride (a-SiN:H) and amorphous silicon carbide (a-SiC:H). In addition, multilayer thin films consisting of various combinations of silicon-based materials have also been proposed to address this issue. Such combinations include a-SiC:H/a-Si:H multilayers [2] and a-SiNx/a-Si multilayers [3].

For this study, the multilayer samples, fabricated using plasma enhanced chemical vapour deposition (PECVD), is made up of 16 alternating layers comprising of a-SiC:H (well layer) and a-Si3N4:H (barrier layer), sandwiched by buffer layers of a-Si3N4:H. Two samples, labeled as S15 and S16, were fabricated by varying the thickness of the well layer. The well layer thickness is 2 nm and 4 nm for S15 and S16 respectively. As for the barrier thickness, it is fixed at 7 nm for both samples. Another a-SiC:H bulk material labeled as S13 will be used as a reference.

Steady-state photoluminescence (PL) and time-resolved photoluminescence measurements were conducted to investigate the PL properties and decay characteristics of the material. The emission intensity of the multilayer samples is much higher compared to the bulk material due to electron-hole localization induced by the quantum-well structure. A blue shift of the peak wavelength is also observed due to sample S15 having a wider gap in the bandtail states and higher bandgap.