Structural characterization and surface polarity determination of polar ZnO films prepared by MBE

Study of Gallium-Doped Zinc Oxide Thin Films Processed by Atomic Layer Deposition and RF Magnetron Sputtering for Transparent Antenna Applications

Gallium-doped zinc oxide (GZO) films were fabricated using RF magnetron sputtering and atomic layer deposition (ALD). The latter ones demonstrate higher electrical conductivities (up to 2700 S cm-1) and enhanced charge mobilities (18 cm2 V-1 s-1). The morphological analysis reveals differences mostly due to the very different nature of the deposition processes. The film deposited via ALD shows an increased transmittance in the visible range and a very small one in the infrared range that leads to a figure of merit of 0.009 Ω-1 (10 times higher than for the films deposited via sputtering). A benchmarking is made with an RF sputtered indium-doped tin oxide (ITO) film used conventionally in the industry. Another comparison between ZnO, Al:ZnO (AZO), and Ga:ZnO (GZO) films fabricated by ALD is presented, and the evolution of physical properties with doping is evidenced. Finally, we processed GZO thin films on a glass substrate into patterned transparent patch antennas to demonstrate an application case of short-range communication by means of the Bluetooth Low Energy (BLE) protocol. The GZO transparent antennas' performances are compared to a reference ITO antenna on a glass substrate and a conventional copper antenna on FR4 PCB. The results highlight the possibility to use the transparent GZO antenna for reliable short-range communication and the achievability of an antenna entirely processed by ALD.

Effects of Surface Polarity on the Structure and Magnetic Properties of Co Implanted and Co-Sm Co-Implanted Polar ZnO Films

We present a comprehensive experimental and theoretical study of the effects of surface polarity on the structure and ferromagnetic properties of Co implanted and Co-Sm co-implanted polar ZnO films deposited on sapphire substrates by molecular beam epitaxy. Substantial intrinsic ferromagnetism (FM) is found for all the implanted polar ZnO films. The magnetization of O-polar ZnO is observed to be higher than that of Zn-polar ZnO under the same implantation conditions, and the magnetization is enhanced for Co-Sm co-implanted ZnO in contrast with unimplanted and Co implanted films. First-principles calculations reveal that the Sm 4f and Co 3d states have strong hybridization with the O 2p state in O-polar ZnO, leading to larger magnetic moments for Co and Co-Sm substituting Zn atoms on the O-polar surface. Meanwhile, X-ray photoelectron spectroscopy results confirm that more oxygen vacancies are introduced into O-polar films by implantation and annealing. We consider that the stronger ferromagnetism in O-polar ZnO is associated with the combined influence of more oxygen vacancies and larger local moments related to Co and Sm doping. These results not only contribute to understanding the origin of FM in diluted magnetic semiconductors but also highlight the feasibility of developing polar spintronic devices for future polar thin film systems.