Burstein-Moss shift and Urbach energy recovery in AZO nanowires via Ar/H2 atmospheric plasma treatment

Abstract

This study presents a combined doping and post-treatment strategy to tune the optical properties of hydrothermally synthesized ZnO nanowires. Aluminum (Al³⁺) doping increased the bandgap from 3.17 eV (undoped ZnO) to 3.23 eV via the Burstein-Moss effect but introduced significant disorder, as indicated by a rise in Urbach energy from 0.025 eV to 0.48 eV. To address this, a low-temperature Ar/H₂ atmospheric pressure plasma jet (APPJ) treatment was applied, further widening the bandgap to 3.27 eV and reducing the Urbach energy to 0.027 eV. We report a 94.4% recovery in optical quality relative to untreated AZO. Optical emission spectroscopy confirmed the presence of hydrogen radicals and ionized argon species essential for defect passivation. The electron temperature, determined from Cu II Boltzmann analysis, was ~5294 K. These findings demonstrate that plasma hydrogenation effectively mitigates doping-induced disorder and enhances the structural order of ZnO nanostructures, offering a viable post-synthetic method for tailoring optoelectronic materials.