Growth of Hexagonal Delafossite CuCrO ₂ Thin Films via Molecular Beam Epitaxy

With the continuous need for faster, smaller, and more energy-efficient electronics and with traditional scaling of silicon-based semiconductor technology reaching its limits, there is a surge for materials with superior properties. Among those are functional oxides, which can have applications as a semiconductor, conductor, ferroelectric, ferromagnet, or superconductor. Within the functional oxides, quasi-2D delafossite minerals such as CuCrO 2 are of special interest since they have the potential of high hole mobility, which opens the way toward high-performance p -type thin-film transistors. In this paper, we report on the layer-by-layer growth of CuCrO 2 delafossite thin films on Al 2 O 3 surfaces via atomic-oxygen-assisted molecular beam epitaxy (MBE) at growth temperatures near 700 °C. The structural quality of the epitaxial films is demonstrated by X-ray diffraction and high-resolution scanning transmission electron microscopy. Moreover, tailoring of the growth parameters in the layer-by-layer approach enables us to achieve the CuCrO 2 hexagonal phase, coexisting with the commonly reported rhombohedral CuCrO 2 phase. The flexibility and high level of control over growth conditions provided by layer-by-layer MBE offer great potential for stabilizing specific phases of the layered delafossite materials.