Structural and optical properties of Si nanocrystals embedded in SiO2/SiNx multilayers

Si nanocrystals (Si-ncs) embedded in SiO2/SiNx multilayer structures can be of interest for optoelectronic devices such as solar cells. However, controlling the size and density of the Si-ncs is strongly requested for an efficient use in a functioning solar cell device. In this work, SiO2 and Si-rich Si3N4 (SRN) layers have been deposited alternatively on a silicon wafer in an electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) using N2O, NH3 and SiH4 gases. The Si-ncs can be obtained in the SRN layers after thermal annealing, thanks to the phase separation between the Si atoms in excess and the matrix. The SiO2 layers allow the Si clusters’ spatial confinement in the SRN film and are also used as a barrier of diffusion. The amount of Si atoms in excess can be controlled by the gas flow ratio. The structural characteristics of Si-ncs density have been investigated by conventional TEM and HR-TEM for different silicon nitride layer thicknesses. Their optical properties were studied by photoluminescence (PL) spectroscopy. Results clearly show a room temperature PL in the visible range, which is of interest for the solar cells applications