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 CuCrO2 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 CuCrO2 delafossite thin films on Al2O3 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 CuCrO2 hexagonal phase, coexisting with the commonly reported rhombohedral CuCrO2 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.