Nonlinear Optical Study of Nano-Sized Effects in a-Si: H Thin Films Deposited by RF-Glow Discharge

Abstract

We have evidenced the high sensitivity of infrared-induced second harmonic generation (IR-ISHG) to the structural changes occurred in amorphous hydrogenated silicon films (a-Si: H) prepared by RF-glow discharge technique at different substrate temperatures and doping types. In every case, a maximal signal of the IR-induced SHG is achieved at temperature of about 110 K and pump-probe delaying time about 22–39 ps. It indicates a marked effect of doped subsystems in the observed nonlinear optical effects. A substantial effect of doping is established from a drastic change of the IR-induced SHG behavior presenting an anomaly at about 400 MW/cm2for a pumping power with wavelength 1.54μm. A minimum of the SHG is observed in that case for standard nondoped films. Note here that the doping type does not affect the behavior of the second-order nonlinear optical susceptibility. The thermo annealing leads to a slight decrease of the effective second-order susceptibilities. Larger changes are observed with doped samples for the pump-probe delaying time from about 39 till 24 ps.