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The epitaxial growth of technically important β-Ga 2 O 3 semiconductor thin films has not been realized on flexible substrates due to the limitations of high-temperature crystallization conditions and lattice-matching requirements. We demonstrate the epitaxial growth of β-Ga 2 O 3 (-201) thin films on flexible CeO 2 (001)-buffered Hastelloy tape. The results indicate that CeO 2 (001) has a small bi-axial lattice mismatch with β-Ga 2 O 3 (-201), inducing simultaneous double-domain epitaxial growth. Flexible photodetectors are fabricated on the epitaxial β-Ga 2 O 3 -coated tape. Measurements reveal that the photodetectors have a responsivity of 4 × 10 4 mA/W, with an on/off ratio reaching 1000 under 254 nm incident light and 5 V bias voltage. Such a photoelectrical performance is within the mainstream level of β-Ga 2 O 3 -based photodetectors using conventional rigid single-crystal substrates. More importantly, it remained robust against more than 20,000 bending test cycles. Moreover, the technique paves the way for the direct in situ epitaxial growth of other flexible oxide semiconductor devices in the future.

In present work, we report a room-temperature ozone sensor using InGaZnO (IGZO)-decorated amorphous Ga 2 O 3 (a-Ga 2 O 3 ) thin films. The gas sensing tests demonstrate that the topmost IGZO modification can significantly promote the sensors' responsivity. Intriguingly, the sensing capability presents a first increasing and then decreasing tendency as the surface morphology of IGZO develops from dispersed particles to a continuous film. Finite difference time domain (FDTD) simulation results prove that IGZO nanoparticles can remarkably increase the surface density of photogenerated electrons, clearly manifesting a strong dependence on IGZO particle size and contributing to the boosted responsiveness. However, once IGZO particles coalesce into a thin film, the ozone sensor's responsivity starts to decrease even though the number of photogenerated carriers still increases. The smaller specific surface area of IGZO thin film is believed to be responsible for this phenomenon. The proposed ozone gas sensors own the merits of low cost, room-temperature detection, easy integration, and mass production, significantly expanding the application fields of a-Ga 2 O 3 thin film.