Effect of ambient air flow on resistivity uniformity of transparent Ga-doped ZnO film deposited by atmospheric pressure plasma jet

Transparent gallium-doped zinc oxide films were deposited on large area (117 mm x 185 mm) glass substrates by atmospheric pressure plasma jet method, using two different enclosure conditions-with and without side opening boundary. The opening allows gas exchange between the growth ambient and outside atmosphere. The spatial resistivity distribution was apparently influenced by the air flow field. The case with side opening has higher overall non-uniformity, and the film near the opening has the highest resistivity, caused by considerable reduction in carrier concentration (-32%) and mobility (-15%). Computer fluid dynamics simulations show that air was drawn in, through the side opening, from outside atmosphere, resulting in a much higher oxygen mass fraction (+50%) near the opening. As such, the film near the opening was deposited in O-rich conditions. The degradation of electrical conductivity in O-rich conditions cannot be explained by oxygen vacancies. We suggest that it is due to the formation of dopant-defect complex Ga-Zn-V-Zn (the lowest formation energy) and reduction of hydrogen impurity (reduced hydrogen partial pressure) in O-rich conditions. Therefore, the tool enclosure, gas flow field, and scanning trajectory must be carefully designed to achieve minimum resistivity non-uniformity on large-area substrates. (c) 2018 Elsevier B.V. All rights reserved.