Study of sub-band states formation in the optical band gap of CuGaS2 thin films by electronic excitations

Abstract

The impacts of electronic excitations with three different ion beams, namely Au, Ag, and O ions at 100–120 MeV and fluences of 5 × 1012 ions/cm2, on the structural, optical, morphological, and electrical properties of spray-deposited CuGaS2 (CGS) thin films have been investigated. Powder X-ray diffraction and micro-Raman spectroscopy measurements have revealed a significant modification in crystallinity and an increase in crystallite sizes after irradiation. Atomic force microscopy (AFM) has revealed variations in surface roughness root-mean-square values and grain size following ion irradiation. UV/Vis-NIR spectroscopy has shown that ion-irradiated films exhibit a redshift compared to pristine CGS, attributable to the creation of new sub-band states between the conduction and valence bands. The resistivity of a CGS thin film changed from 5.33 × 10−2 Ωcm to 1.30 × 10−2 Ωcm, 9.6 × 10−2 Ωcm, and 9.63 × 10−2 Ωcm, respectively, after Au-, Ag-, and O-ion-irradiations. The highest photocurrent of 1.196 mA was observed for the Au-ion-irradiated CGS film. By comparing all of the results, it is concluded that an Au-ion-irradiated CGS thin film may act as a suitable photo-absorber for photovoltaic applications.