Structural and optical properties of Si nanocrystals embedded in SiO 2/SiN x multilayers

Abstract

Si nanocrystals (Si-ncs) embedded in SiO 2/SiN x 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, SiO 2 and Si-rich Si 3N 4 (SRN) layers have been deposited alternatively on a silicon wafer in an electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) using N 2O, NH 3 and SiH 4 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 SiO 2 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.