Absorption spectra of nanocrystalline silicon embedded in SiO₂ matrix

Nanocrystalline silicon embedded SiO₂ matrix is formed by annealing the SiO_x films fabricated by plasma enhanced chemical vapor deposition technique. Absorption coefficient and photoluminescence of the films have been measured at room temperature. The experimental results show that there exists an exponential absorption in the spectral range of 2.0-3.0 eV. The relationship of (αhν)^1/2∝(hν-E_g) demonstrates that the luminescent nanocrystalline silicon has an indirect band structure. The existence of Stokes shift between photoluminescence and absorption edge indicates that radiative combination can take place not only between shallow trap states of electrons and holes but also between quantized states of electrons and holes.