Doping Mechanism in Transparent Conductive ZnO Films Grown by Atomic Layer Deposition
In this presentation, we report structural and electrical properties of ‘atomic-layer-doped’ ZnO films.[1,2] Firstly, Al-doped ZnO films were deposited by ALD via alternate stacking of a ZnO matrix and AlOx dopant layers. Scanning TEM-HAADF analysis revealed that the ALD-AZO films have a unique layer-by-layer structure as those were grown. Upon correlation of the structural and electrical properties, effects of the layer-by-layer doping manner were interpreted in order to investigate a carrier generation mechanism of the ALD-AZO films. In the latter part, efforts of optimizing electrical properties of ALD-ZnO films will be given by controlling surface coverage of dopant ions incorporated in each atomic-doping layer. These efforts include two approaches; i) control of the amount of Al ions deposited during 1 ALD cycle of AlOx via process-parameter adjustment, and ii) introduction of other dopant oxides (group III: In, B, transition metals: Hf, Zr, Ti) which have different surface coverage. Among the tested dopants, it is remarkable that Ti exhibited the highest electrical conductivity (950 S/cm) and doping efficiency (51%). This finding is extraordinary compared to the conventional homogeneous compounds where Al has long been considered as one of the best dopants for the ZnO.
 D.-J. Lee, K.-B. Kim et al., Adv. Funct. Mater. 21, 448 (2011).
 D.-J. Lee, K.-B. Kim et al., J. Electrochem. Soc. 158, D277 (2011).