Formation and photoluminescence of Si nanocrystals in controlled multilayer structure comprising of Si-rich nitride and ultrathin silicon nitride barrier layers

The effect of ultrathin silicon nitride (Si3N4) barrier layers on the formation and photoluminescence (PL) of Si nanocrystals (NCs) in Si-rich nitride (SRN)/Si3N4 multilayer structure was investigated. The layered structures composed of alternating layers of SRN and Si3N4 were prepared using magnetron sputtering followed by a different high temperature annealing. The formation of uniformly sized Si NCs was confirmed by the transmission electron microscopy and X-ray diffraction measurements. In particular, the 1 nm thick Si3N4 barrier layers was found to be sufficient in restraining the growth of Si NCs within the SRN layers upon high annealing processes. Moreover, X-ray photoelectron spectroscopy spectra shown that films subjected to post-anneal processes were not oxidized during the annealing. X-ray reflection measurements revealed that high annealing process induced low variation in the multilayer structure where the 1 nm Si3N4 layers act as good diffusion barriers to inhibit inter-diffusion between SRN layers. The PL emission observed was shown to be originated from the quantum confinement of Si NCs in the SRN. Furthermore, the blue shift of PL peaks accompanied by improved PL intensity after annealing process could be attributed to the effect of improved crystallization as well as nitride passivation in the films. Such multilayer structure should be advantageous for photovoltaic applications as the ultrathin barrier layer allow better electrical conductivity while still able to confine the growth of desired Si NC size for bandgap engineering.