Deposition of transparent and conductive ZnO films by an atmospheric pressure plasma-jet-assisted process

• Report an atmospheric pressure plasma-assisted process for ZnO film deposition.
• Conductive and transparent ZnO films are deposited.
• ZnO deposition without post-annealing steps and without intentional doping.
• Film with resistivity of 1.4 Ω-cm can be obtained.
• Zn5(OH)8Cl2 is an intermediate for the precursor to ZnO conversion process.

In this work, deposition of transparent and conductive ZnO thin films using an atmospheric pressure plasma jet (APPJ) is presented. The APPJ is sustained by a pulsed power source with a repetitive frequency up to 25 kHz using N2 as the plasma gas. ZnCl2 solution is used as the precursor and is nebulized and then sprayed into the downstream of the APPJ. With sufficiently long retention time and high jet temperature, a nearly full conversion of the precursor to ZnO occurs. Zinc hydroxyl chloride, with sheet-like structures, is formed as the intermediate when the precursor is not fully converted to ZnO. With an optimal condition, ZnO films with a resistivity of 1.4 Ω-cm and average transmittance between 400 and 800 nm of greater than 80% can be obtained with the root-mean-square surface roughness approximately 10 nm. This demonstrates a one-step and fast process without the need of post-annealing steps and intentionally doping to fabricate transparent and conductive ZnO films.