Si-doped zinc oxide transparent conducting oxides; nanoparticle optimisation, scale-up and thin film deposition

Abstract

Silicon-doped zinc oxide, Zn_1−xSi_xO_y, transparent conducting oxide nanoparticles were prepared using a laboratory scale (production rate of 60 g h⁻¹) continuous hydrothermal flow synthesis (CHFS) process in the dopant range 0.25 to 3.0 at% Si. The resistivity of the materials was assessed as pressed heat-treated pellets, revealing that the sample with the lowest resistivity (3.5 × 10⁻² Ω cm) was the 0.25 at% Si doped ZnO sample. The synthesis of this optimum composition was then scaled up to 350 g h⁻¹ using a larger pilot plant CHFS process. Spin coating of a slurry of the resulting nanopowder made on the pilot plant, followed by an appropriate heat-treatment, produced a thin film with an optical transmission >80% and a low resistivity of 2.4 × 10⁻³ Ω cm, with a carrier concentration of 1.02 × 10²⁰ cm⁻³ and a mobility of 11 cm² V⁻¹ s⁻¹. This is a factor of almost twenty times improvement in the resistivity versus the analogous pressed, heat-treated pellet.