Modification of the nonlinear optical absorption and optical Kerr response exhibited by nc-Si embedded in a silicon-nitride film

We studied the absorptive and refractive nonlinearities at 532 nm and 26 ps pulses for silicon-nitride films containing silicon nanoclusters (nc-Si) prepared by remote plasma-enhanced chemical vapor deposition (RPECVD). Using a self-diffraction technique, we measured for the as-grown sample beta=7.7x10(-9) m/W, n(2)=1.8 x 10(-16)m(2)/W, and vertical bar chi((3))(1111)vertical bar = 4.6 x10(-10)esu; meanwhile, when the sample was exposed to an annealing process at 1000 degrees C during one hour in a nitrogen atmosphere, we obtained beta=-5x10(-10)m/W, n(2)=9x10(-17)m(2)/W, and vertical bar chi((3))(1111)vertical bar = 1.1 x10(-10)esu. A pure electronic nonlinear refraction was identified and a large threshold ablation of 41 J/cm(2) was found for our films. By fitting nonlinear optical transmittance measurements, we were able to estimate that the annealed sample exhibits a response time close to 1 fs. We report an enhancement in the photoluminescence (PL) signal after the annealing process, as well as a red-shift due to an increment in size of the nc-Si during the thermal process. (C) 2009 Optical Society of America