Evidence of quantum size effect in nanocrystalline silicon by optical absorption

Abstract

The optical absorption spectrum in nanocrystalline silicon $(n\ensuremath{-}\mathrm{Si})$ was determined from both light transmittance and reflectance measurements. We observed that $n\ensuremath{-}\mathrm{Si}$ has a phonon structure in the optical absorption spectrum. This structure originates from momentum-conserving TO phonon absorption and emission, and provides direct evidence that $n\ensuremath{-}\mathrm{Si}$ is an indirect-band-gap semiconductor with quantum size effects. By using small-angle x-ray scattering to measure the nanocrystal size distribution, we found that the band-gap widening varies as ${(1/L)}^{1.6}$ with decreasing nanocrystal diameter L.