Optical absorption in /spl mu/c-Si:H films induced by oxygen

Extra optical absorption in /spl mu/c-Si:H films at photon energy of 0.7/spl sim/1.2 eV caused by impurity has been studied by resonant photothermal bending spectroscopy. The extra absorption increases by thermal annealing in air. And, the absorption coefficient was not changed by carbon contamination in /spl mu/c-Si:H film. Thus, we propose that the origin of the extra absorption is localized states related to oxygen impurity in the film. In addition, the extra optical absorption has negative temperature coefficient at the temperature region of 25/spl sim/150/spl deg/C. And, the energy level of the localize state caused by the oxygen exists around 0.7 eV from band edge. From these results, we proposed that the localized state exists in the grain boundaries including amorphous Si structure.