Transferable GaO Membrane for Vertical and Flexible Electronics via One-Step Exfoliation.

Transferable GaO thin film membrane is desirable for vertical and flexible solar-blind photonics and high-power electronics applications. However, GaO epitaxially grown on rigid substrates such as sapphire, Si, and SiC hinders its exfoliation due to the strong covalent bond between GaO and substrates, determining its lateral device configuration and also hardly reaching the ever-increasing demand for wearable and foldable applications. Mica substrate, which has an atomic-level flat surface and high-temperature tolerance, could be a good candidate for the van der Waals (vdW) epitaxy of crystalline GaO membrane. Beyond that, benefiting from the weak vdW bond between GaO and mica substrate, in this work, the GaO membrane is exfoliated and transferred to arbitrary flexible and adhesive tape, allowing for the vertical and flexible electronic configuration. This straightforward exfoliation method is verified to be consistent and reproducible by the transfer and characterization of thick (∼380 nm)/thin (∼95 nm) κ-phase GaO and conductive n-type β-GaO. Vertical photodetectors are fabricated based on the exfoliated GaO membrane, denoting the peak response at ∼250 nm. Through the integration of Ti/Au Ohmic contact and Ni/Ag Schottky contact electrode, the vertical photodetector exhibits self-powered photodetection behavior with a responsivity of 17 mA/W under zero bias. The vdW-bond-assisted exfoliation of the GaO membrane demonstrated here could provide enormous opportunities in the pursuit of vertical and flexible GaO electronics.