Enhancement of defects induced optical nonlinearity in Al: ZnO thin films by electron beam

Controlling and understanding effects induced by electron beam irradiation is quite important to validate the enhanced optical nonlinearity exhibited by Al: ZnO thin films. Herein, we report the generation and controlling of defects by electron beam irradiation in Al: ZnO thin films. The X-ray photoelectron spectroscopy studies on the films confirm the reduction in oxygen-related radiative defect concentration on electron beam irradiation. The structural studies by glancing angle x-ray diffraction shows inclusion of lattice stress in the films upon electron beam irradiation. A drastic increase in the Raman peak intensity along with a shift and broadening of peaks were observed upon irradiation. The increment in the Raman modes intensity endorses that irradiation treatment has enhanced the structural defect centers in the films. The PL studies show a decrement in the emission intensity confirming the decrement of radiative defects in the films. The optical nonlinearity of the films shows an increment in signal intensity attributed to the variation in ground state dipole moments of the atoms investigated using laser stimulated third harmonic generation technique. The Z-scan studies endorses electron beam assisted enhancement in thermal lensing mechanism and free-carrier absorption induced two-photon absorption resulted in the enhancement of third-order optical susceptibility from 6.81 × 10^-4 esu to 31.3 × 10^-4 esu.