Electronic transport modulation in spray-pyrolyzed ZnO thin films via Ar-H2, Ar-O2, and Ar-N2 plasma treatments

Abstract

This study demonstrates the modulation of electronic transport properties in spray-pyrolyzed ZnO thin films through atmospheric pressure plasma jet (APPJ) treatments with Ar-based reactive gas environments (Ar-H₂, Ar-N₂, and Ar-O₂). Electrochemical Impedance Spectroscopy (EIS) revealed that plasma exposure significantly alters interfacial and bulk resistances, with Ar-H₂ treatment reducing polarization resistance (R_P) from 704.1 Ω (untreated) to 76.91 Ω after 90 seconds, indicative of enhanced charge transfer due to hydrogen-induced defect passivation. In contrast, Ar-N₂ plasma produced variable increases in series resistance (R_S) and moderate changes in R_P, suggesting complex nitrogen incorporation effects, while Ar-O₂ treatment led to a marked decrease in R_P to 57.51 Ω, consistent with increased oxygen vacancy-mediated conductivity. Optical emission spectroscopy (OES) confirmed the generation of key reactive species for each plasma condition, and electron temperatures for hydrogen and oxygen plasmas were determined using Cu II spectral lines and Boltzmann analysis. These results establish that APPJ processing enables precise defect engineering in ZnO thin films, offering a robust route for tuning their electronic characteristics for advanced sensor and optoelectronic applications.