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

J Ebothé,K J Plucinski,I V Kityk,K Nouneh,P Roca I Cabarrocas

doi:10.1155/jnm/2006/63608

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/cm2 for a pumping power with wavelength 1.54 μm. 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.

Highlights

Amorphous hydrogenated silicon (a-Si : H) films are promising optoelectronic materials used as solar cell or other optoelectronic devices requiring additional investigations for a rigorous control of defects in the subsystems formed
The role of deposition temperature on the second-order harmonic generation (SHG) behavior of a-Si : H films is evidenced in Figure 4 through the study of the second-order susceptibility
Sample S3 deposited at 50◦C exhibits a higher response than S1 obtained at 150◦C. Their particular maximum nonlinear optical (NLO) signals appear at about 120 K

Summary

Introduction

Amorphous hydrogenated silicon (a-Si : H) films are promising optoelectronic materials used as solar cell or other optoelectronic devices requiring additional investigations for a rigorous control of defects in the subsystems formed. These defects are crucially dependent on the method used and the conditions applied in the sample elaboration. The reduction observed elsewhere below 100◦C [3, 4] has been explained either by the decrease of the deposition rate giving enough time to manifold precursors SiH3 radicals to find the most favorable sites for incorporation into the film [5] or by the reduction of the polymerization process [6] Another important aspect to be considered is the film’s doping. The results obtained from dc-conductivity and IR spectra cannot provide information concerning the hyperfine influence of the trapping levels formed by interfaces

Methods

Results

Conclusion