Formation of High Bandgap CuIn(S,Se)2 Alloys from CuInSe2 Thin Film by a Simple (NH4)2Sx Immersion

In this work, we studied the effect of the additive, antimony, and chemical sulfurization on CuInSe₂ thin films with (NH₄)₂S_x solution. The CuInSe₂ thin films were deposited by molecular beam deposition method and trace amounts of antimony was added. The antimony, determined by Scanning Auger Electron Microscope, is concluded to react with the bi- or tri-coordinated In to saturate the dangling bonds on the growing surface as surfactants. During (NH₄)₂S_x sulfurization, the sulfur atoms enter thin films through a pathway, which is created by the replacement of antimony atoms segregated on the thin film surface ‚ and simultaneously, a portion of the selenide film is transformed into the alloy of CuInSe₂ and CuInS₂ on the grain surface. Significant amount of sulfur(35%)distribute throughout the thin film of CuInSe₂ under an antimony source temperature of 510° C in the film growth, and an increase of energy bandgap up to 1.3eV was determined. The chemical reactions are justified from a thermodynamic consideration.