Near infrared absorption of Si nanoparticles embedded in silica films

The absorption coefficient of Si nanoparticles embedded in a silica matrix obtained through thermal annealing at 1000 °C of SiO thin films has been determined by a combination of ellipsometry and photothermal deflection spectroscopy. The high absorption level below 2 eV was explained by the superposition of the contribution of: (i) extended states and distorted bond states (Urbach tail), giving rise to an exponential regime of the variation of the absorption coefficient on energy and (ii) point defect states. The value of the characteristic energy of the exponential regime was found above 200 meV. This high value was partly related to the high stress present at the np-Si/SiO2 interface. The point defects were attributed to dangling bonds and induced an additional absorption band located near 1.2 eV contributing to above 100 cm−1 to the absorption at this energy.