Nonlinear optical dynamics in CdSe/Bi2O3 thin films

Abstract

Herein, thermally evaporated CdSe thin films are interfaced with Bi2O3 nanosheets to construct a conduction band aligned heterojunction device suitable for nonlinear optical applications. Depositing of Bi2O3 nanosheets onto CdSe, increased the crystallite size and decreased the strain and line defects concentration by 15.4%, 12.2% and 23.1%, respectively. Bi2O3 nanosheets successfully narrowed the energy band gap of CdSe. The absorption improved by 403%, and optical conductivity, dielectric constant and terahertz cutoff frequency are increased by 498% 60% and 302% near 1.65 eV, respectively. In addition, formation of zero conduction band offset and large valence band offset of 1.55 eV, resulted in high drift mobility and free carrier density values of 27.75 cm2/Vs and 4.0 making the device attractive for terahertz transistors technology. Moreover, the calculated first and third order nonlinear susceptibility exhibited values of 0.3–0.5 esu, 10−11-10−12 esu, respectively. Bi2O3 coating onto CdSe resulted in the enhancement in the nonlinear refractive index by more than 100%. The enhancement reached 1000% at 1.80 eV. The response of the CdSe/Bi2O3 to the intensity of light passing through it improved by 300%. Furthermore, the ratio of the volume energy loss factor to the surface energy loss factor is always larger than one indicating the domination of the bulk plasmonic excitations which are essential in plasmonic applications.