Plasma-Enhanced Atomic Layer Deposition of p-Type Copper Oxide Semiconductors with Tunable Phase, Oxidation State, and Morphology
Julia D. Lenef, Jaesung Jo, Orlando Trejo, David J. Mandia, Rebecca L. Peterson, Neil P. Dasgupta
Abstract
Metal oxide semiconductors are important due to their diverse set of applications in (opto)electronics including light-emitting diodes, solar cells, and thin film transistors (TFTs). However, compared to their n-type counterparts, p-type oxide thin films are less often reported, and there is a need for increased fundamental understanding of their process-structure–property relationships. In this study, p-type CuOx was grown by plasma-enhanced atomic layer deposition (PE-ALD) using different ratios of hydrogen and oxygen plasma and a nonfluorinated copper amidinate precursor. This approach, combined with postdeposition annealing, enables tuning of the phase, oxidation state, and morphology of the films. Here, we comprehensively investigate the coupled relationships between: (1) PE-ALD process parameters; (2) oxidation state, composition, and grain size; and (3) electronic properties of the films. Synchrotron X-ray absorption spectroscopy was performed to quantify the copper oxidation states. By varying the hydrogen:oxygen plasma ratio, the phase of CuOx can be controlled to form Cu, Cu2O, or CuO. Vacuum annealing resulted in an increase in grain size and reduction in copper oxidation state. To study the p-type semiconductor behavior, bottom-gate TFTs were fabricated, demonstrating characteristic I–V behavior with an on/off current ratio of ∼105 for the film with the largest Cu(I) fraction and largest grain size.