Rational Molecular Design for Non-aqueous Atomic Layer Deposition of Zinc Oxide

Abstract

Zinc oxide (ZnO) is a transparent wide band gap semiconductormaterialwith various possible applications in form of thin films. Most previousstudies on atomic layer deposition (ALD) of ZnO thin films utilizeda few well-known processes with diethylzinc (DEZ) and counter-reactantssuch as H2O and O-3. However, O-3 andH(2)O reactants have relatively strong reactivity, so thatthey are not suitable for substrates sensitive to oxidation. Therefore,development of milder non-aqueous alternative ALD process for ZnOis highly desired. In this study, we introduce ALD of ZnO using alcoholswith theoretically optimized molecular structure. To discover suitablealcohol reactants for ZnO ALD, reaction pathways and reactivity betweenvarious types of alcohol reactants with surface-ethyl groups wereevaluated through density functional theory calculations. It was foundthat unsaturated allylic alcohols would have the lowest activationenergy for ZnO ALD via an allylic rearrangement mechanism. Experimental,novel ALD processes for ZnO using DEZ with alcohol as oxygen sourcesare set up. Ethanol as a typical simple alcohol is compared to 2-methyl-3-buten-2-ol(MBO) as an alcohol with optimal molecular structure setup. ALD ZnOfilms using MBO showed processes and material properties comparableto those of H2O-ALD ZnO. ZnO thin films as transparentconducting oxide could be obtained, and device performances of thin-filmtransistors based on alcohol-ALD processes are evaluated.