Influence of paramagnetic defects on multicolored luminescence from nanocrystalline silicon

We report on the correlation between paramagnetic defects and the luminescent properties of nanocrystalline silicon (nc-Si) using electron spin resonance (ESR) and photoluminescence measurements. Nanocrystalline silicon having particle sizes from 1.9to3.0nm exhibited continuous luminescence from blue to red wavelengths. However, the density of nc-Si decreased as the luminescent color was shifted towards blue. Red/green/blue luminescent nc-Si contained three kinds of ESR centers, two nonradiative recombination centers (an a center and a Pb center), and a radiative recombination center (a Pce′ center). The a, Pb, and Pce′ centers originate from a Si dangling bond in nc-Si, a Si dangling bond in the nc-Si/silicon dioxide (SiO2) interface region, and electrons trapped in localized states close to the conduction band edge in the vicinity of the nc-Si surface, respectively. The spin densities of the Pb and Pce′ centers increased with the blueshift of the luminescent color. Increasing the spin density of the Pb center and reducing the density of nc-Si led to a reduction in the intensity from the red to the blue luminescence. These results indicate that this reduction in intensity as the emission was shifted towards blue was due to the presence of many Pb centers in a single particle and the generation of a little density of nc-Si.