Origin of the giant optical nonlinearity of Sb2Te3 phase change materials

We report the giant optical nonlinear absorption and refraction of Sb2Te3 phase change materials at low laser irradiation intensities. The nonlinear absorption and refraction coefficients reach up to -6.63 x 10(-2) m/W and 2.606 x 10(-9) m(2)/W, respectively. The first principles calculation indicates that the giant nonlinear absorption stems from the band filling effect of the photon induced free carriers under laser irradiation. The band-gap shrinking results in a positive thermo-optic coefficient, thus the giant nonlinear refraction. The numerical results are generally correlated with the experimental findings from z-scan and temperature-variable ellipsometric measurements. (C) 2010 American Institute of Physics. [doi:10.1063/1.3530428]