Influence of the size dispersion on the emission spectra of the hydrogen passivated Si nanoparticles in SiNx

Abstract

The influence of the size dispersion on the emission spectra of the hydrogen passivated silicon nanopaticles (Si NPs) in silicon nitride thin films, which are grown by helicon wave plasma-enhanced chemical vapor deposition (HWP-CVD) technique with SiH₄, H₂ and Ar-diluted 6.25% N₂ as the reactant gas sources, have been investigated. Transmission electron microscopy examination shows that Si NPs are isolated from the others by silicon nitride barriers and the sizes of Si NPs in silicon nitride matrix are distributed within a wide range. The luminescent due to quantum confinement effect of Si NPs embedded in the SiNx matrix was guaranteed by adding H₂ into film deposition process. The emission correlated to the defects such as excess silicon voids and nonradiative recombination centers have been suppressed and a strong PL with a wide band was observed. The photoluminescence (PL) spectra were investigated under different excitation energy (<i>E_ex</i>). It is shown that both the PL peak energy and their full width at half maximum (FWHM) show a decrease trend with decreasing the <i>E_ex</i>, and no obvious PL can be observed when the <i>E_ex</i> lower than a certain <i>E_ex</i>. And at high excitation energy contribution of the smaller particles in size becomes remarkable larger, thus it may be extremely difficult to correlate the PL spectra with the mean size of the Si NPs. These results are explained by quantum confinement effect model taking into account there existing a size distribution of Si NPs in the SiNx matrix.