Non-linear optical diagnostic of a-Si:H thin films deposited by RF-glow discharge

We have evidenced the high sensitivity of infra red-induced second harmonic generation (IR-ISHG) to the structural changes that 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 a temperature of about 110 K and pump-probe delaying time about 22-38 ps. This one indicates a marked effect of doped subsystems in the observed non-linear optical effects. A tremendous effect of doping is established from a drastic change of the IR-induced SHG behavior presenting an anomaly at about 400 MW/cm² for a pumping power with wavelength 3.7 μm. A minimum of the SHG is observed in that case for standard non-doped films. Note here that the doping type does not markedly affect the behavior of the second-order non-linear optical susceptibility. The thermo-annealing leads to a slight decrease of the effective second-order susceptibilities. More drastic changes are observed with doped samples for the pump-probe delaying time from about 39 till 24 ps.