The Role of Counteranions in Solution Deposition of ZnS Thin Films on GaAs

Using 5 commonly employed precursors for Zn²⁺ cations, ZnSO₄, ZnI₂, ZnCl₂, Zn(NO₃)₂, and Zn(CH₃COO)₂, we demonstrate the effect of counterions on ZnS thin film formation. We show that both film nucleation and growth stages are strongly dependent on the Zn²⁺ precursor type. We systematically studied the mechanisms of thin film deposition on GaAs(100), including solution-substrate interactions, Zn²⁺ ion adsorption on the substrate, and nuclei formation as well as stress accumulation during film growth. It was shown that the early stages of film formation play a key role in the subsequent growth kinetics and resulting film quality. X-ray photoelectron spectroscopy, supported by contact angle measurements, transmission electron microscopy, and energy-dispersive spectroscopy showed that increasing the degree of surface oxidation and passivation at the early stages of ZnS film formation inhibits solution desorption. Finally, the previously reported mechanism of crack formation is explored through an interrupted growth series of ZnS films deposited from solutions with different Zn²⁺ precursors.