Spatial atomic layer deposition of ZnO/TiO2 nanolaminates

Abstract

Spatial atomic layer deposition (S-ALD) is a potential high-throughput manufacturing technique offering fast and large scale ultrathin films deposition. Here, an S-ALD system with modular injectors is introduced for fabricating binary oxides and their nanolaminates. By optimizing the deposition conditions, both ZnO and TiO2 films demonstrate linear growth and desired surface morphology. The as-deposited ZnO film has high carrier mobility, and the TiO2 film shows suitable optical transmittance and band gap. The ZnO/TiO2 nanolaminates are fabricated by alternating substrate movement between each S-ALD modular units of ZnO and TiO2. The grazing incidence x-ray diffraction spectra of nanolaminates demonstrating the signature peaks are weaker for the same thickness nanolaminates with more bilayers, suggesting tuning nanolaminates from crystalline to amorphous. Optical transmittances of ZnO/TiO2 laminates are enhanced with the increase of the bilayers' number in the visible range. Refractive indices of nanolaminates increase with the thickness of each bilayer decreasing, which demonstrates the feasibility of obtaining desired refractive indices by controlling the bilayer number. The electronic properties, including mobility, carrier concentration, and conductivity, are also tunable with different bilayers.