Enhancement of the luminescence by the controlled growth of silicon nanocrystals in SRO/SiO2 superlattices

This work reports the study of highly-luminescent silicon nanocrystals (SiNCs) in silicon rich oxide (SRO)/SiO2 multilayers (MLs). Parameters such as silicon excess (Si-excess) and SRO-thickness were modified to evaluate the structure and composition and their effect on the photoluminescence (PL) response of the different superlattices. SRO monolayers with the same silicon excess were also deposited for comparison. Both, monolayers and MLs, emit a broad emission band in the red-orange region (1.45-2.1 eV). The PL of SRO monolayers strongly increases as Si-excess decreases from 10.2 to 5.2 at.%. Nevertheless, SRO/SiO2 MLs allow up to 14-fold PL enhancement as compared to SRO monolayers. A silicon diffusion from SRO nano-layers towards the SiO2 ones reduces the Si content within the SRO allowing the SiNC size reduction (thus increasing the SiNC density) as compared to SRO monolayers. Therefore, the high luminescence is correlated with the SiNCs formation with a mean size below 3 nm where the surface defects (SiO bonds) are strongly active.