Modulation of wall thickness of Al‐doped ZnO nanotubes by nanolamination of atomic layer deposition for oxygen sensing

Abstract The high surface‐to‐volume ratio and feature dimensions of the gas sensors are the key factors for improving the gas response. In this study, a novel method to prepare an Al‐doped ZnO (AZO) nanotube oxygen sensor with tunable wall thickness is reported via the ZnO–Al 2 O 3 nanolamination of atomic layer deposition (ALD) using tris(8‐hydroxyquinoline) gallium nanowire (GaQ 3 NW) as a template. The ALD of Al 2 O 3 significantly enhances wall uniformity and decreases the wall thickness of the AZO nanotubes. In addition, the incorporation of Al 2 O 3 allows full coverage of AZO on GaQ 3 NWs. With an increase in the Al 2 O 3 fraction, the carrier concentration increases, but the depth of the depletion layer and gas response of the nanotube sensor are reduced. The gas response of the nanotubes is inversely proportional to wall thickness, suggesting that it is a function of the surface‐to‐volume ratio. When the wall thickness is decreased to 12 nm, the gas response of AZO nanotubes with 2% Al increases significantly to 7. This can be explained by the grain control model, because thin wall leads to the formation of fully charge‐depleted nanotubes.