Optical dynamics in the Ag/α-Ga₂S₃ layer system

Abstract

In this work, thin films of Ga2S3 are deposited onto 150 nm thick transparent Ag substrate by the physical vapor deposition technique under vacuum pressure of 10(-5) mbar. The films are studied by the X-ray diffraction and optical spectrophotometry techniques. It is found that the Ag substrate induced the formation of the monoclinic alpha-Ga2S3 polycrystals. The transparent Ag substrate also changed the preferred optical transition in Ga2S3 from direct to indirect It also increased the light absorption by 79 and 23 times at incident light energies of 2.01 and 2.48 eV, respectively. In addition, a red shift in all types of optical transitions is observed. Some the extended energy band tails of Ag appears to form interbands in the band gap of Ga2S3. These interbands strongly attenuated the dielectric and optical conduction parameters. Particularly, an enhancement in the dielectric constant values and response to incident electromagnetic field is observed. The Drude-Lorentz modeling of this interface has shown that the free carrier density, drift mobility, plasmon frequency and reduced electron-plasmon frequency in Ga2S3 increases when the Ag substrate replaced the glass or other metals like Yb, Al and Au. The nonlinear optical dynamics of the Ag/Ga2S3 are promising as they indicate the applicability of this interface for optoelectronic applications.