Laser Annealing of Transparent ZnO Thin Films: A Route to Improve Electrical Conductivity and Oxygen Sensing Capabilities

Abstract

The chemical deposition of high-performance Zinc Oxide (ZnO) thin films is challenging, thus significant efforts have been devoted during the past decades to develop cost-effective, scalable fabrication methods in gas phase. This work demonstrates how ultra-short-pulse Laser Beam Scanning (LBS) can be used to modulate electrical conductivity in ZnO thin films deposited on soda-lime glass by Spatial Atomic Layer Deposition (SALD), a high-throughput, low-temperature deposition technique suitable for large-area applications. By systematically optimizing laser parameters, including pulse energy and hatching distance, significant improvements in the electrical performance of 90 nm-thick ZnO films were achieved. The optimization of the laser annealing parameters —0.21 μJ/pulse energy and a 1 μm hatching distance— yielded ZnO films with an electrical resistivity of (9 ± 2) · 10-2 Ω⋅cm, 3 orders of magnitude lower than as deposited films. This result suggests that laser post-deposition-processing can play an important role in tailoring the properties of ZnO thin films. Excessive laser intensity can compromise structural integrity of the films, however, degrading their electrical transport properties.