Quantum confinement dominates band gaps while defects lead the photoluminescence in silicon nanowires.

The quantum confinement effect has been observed in silicon nanowires (SiNWs) and is a widely accepted mechanism for visible photoluminescence (PL). Besides the observed widening of the band gap, an increase in Urbach energy is seen, revealing the presence of structural disorder due to oxygen-related defects. Surprisingly, in contrast to band gap widening, PL spectra showed a spectral shift instead of peak widening. Our finding indicates that oxygen-related defect states have a significant influence on the shifts in PL peaks. The combined influence of the quantum confinement effect and these defect states is demonstrated to play an important role in defining the PL response. This work provides insights into the interplay between quantum confinement and defect states, offering a clearer understanding of PL mechanisms in SiNWs.