Atomic layer-controlled growth of transparent conducting ZnO on plastic substrates

Highly transparent ( T > 80%) and conductive ( ρ ∼ 10 −3 Ω cm) zinc oxide thin films were deposited by atomic layer-controlled growth on a wide variety of substrates, including glass sapphire and flexible polyethylene terephthalate (PET) at temperatures of 100–210°C using diethylzinc (DEtZn) and water. This is the first example of atomic layer-controlled growth or atomic layer epitaxy on a polymer substrate. The growth was accomplished by separating the CVD reaction, Zn(CH 2CH 3) 2 + H 2O → ZnO + 2CH 3CH 3, into the following half reactions: (A) Zn–OH * + Zn(CH 2CH 3) 2 → Zn–O–Zn–CH 2CH 3 * + CH 3CH 3 (B) Zn–CH 2CH 3 * + H 2O → Zn–OH *+CH 3CH 3.The reactions were self-terminating and growth rates from 1.5–1.9 Å/cycle were observed. In order to grow films at higher temperatures and to improve film adhesion, alumina buffer layers were deposited before the ZnO films on PET substrates. The resistivity of the films improved by doping gallium into the films and with increasing temperature. The best film grown on PET had a resistivity of 1.4 × 10 −3 Ω cm, while the best film grown on glass had a resistivity of 8 × 10 −4 Ω cm.