Deposition of highly transparent and conductive Ga-doped zinc oxide films on tilted substrates by atmospheric pressure plasma jet

Abstract

Oblique angle deposition (OAD) has become a cost-effective method for depositing nanostructured films. Films with various degrees of porosity, anisotropy, and crystallographic texture have been successfully demonstrated. However, most studies were based on the more established processes, such as evaporation and sputtering; oblique angle deposition using atmospheric pressure plasma jet (APPJ) has not been reported. Here we deposit Ga-doped zinc oxides (GZO) on tilted substrate using APPJ, and study how the film properties are affected by the oblique angle and nozzle scanning trajectory. We found that the trajectory plays a key role in determining the optoelectronic properties of the obliquely deposited films. If the nozzle scans from the upstream side of the substrate to the downstream side, the resistivity, carrier concentration and mobility deteriorate considerably near the downstream region. The film becomes more porous with the haze factor rising significantly from <5% to ∼80%, while the total transmittance remains high (>80% at 550 nm). This degradation can be attributed to the “pre-deposition” of the GZO adsorbed particles on the downstream side of the bare glass where the nozzle has not scanned. Such undesirable pre-deposition occurs due to the combined effect of asymmetric plasma jet and gas flow, both pointing toward downstream, compared to axial symmetric pattern observed in the normal case. More importantly, this undesirable phenomenon can be removed by merely reversing the scanning trajectory, i.e. from downstream to upstream. In this case, a dense film has been formed in the downstream region so the subsequent exposure of the biased plasma jet and gas flow do not result in ad-particles deposition. Therefore, highly transparent and conductive OAD films as good as the normally deposited films can be achieved, a unique phenomenon not reported before. Our findings may shed light on the development of curved display technology, and may also be applied to other deposition methods with moving nozzle or moving stage such as spray pyrolysis.