Photoluminescence performance limits of Si nanocrystals in silicon oxynitride matrices

Abstract

The present comprehensive study of photoluminescence (PL) quantum yield (QY) of Si nanocrystals (SiNCs) in Si-rich oxynitride (SRON) superlattices was performed over a broad set of samples. The PL QY is sensitive mostly to the thickness of SRON and barrier oxide layers and to the passivation procedures. Annealing in hydrogen improves the QY proportionally to the NC surface area by passivating the NC/oxide interface defects present at a surface density of about 2.5 × 1012 cm−2. The maximum external QY of nearly 30% is found in well-passivated superlattices with a SiNC size of about 4 nm and a SiO2 barrier thickness of 2 nm or larger. We reveal the existence of an extended near-infrared tail of the PL spectra, whose weak intensity anti-correlates with the external QY. The relative intensity of this emission increases with temperature as well as for strong excitation above the PL saturation level and may be related to excitation energy transfer to the structural defects near NCs. Finally, we discuss the possible mechanisms which are responsible for limiting the attainable PL QY and which may be the subject of future efforts to further increase the PL QY.