One-step fabrication of β-Ga2O3–amorphous-SnO2 core–shell microribbons and their thermally switchable humidity sensing properties

Abstract

We reported the fabrication of a highly sensitive, fast, and thermally switchable humidity sensor based on a β-Ga₂O₃–amorphous-SnO₂ core–shell microribbon, which was synthesized via a simple one-step chemical vapour deposition. The as-grown microribbons were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) and the results indicated that the microribbon has a well-defined core–shell structure with β-Ga₂O₃ in the core and amorphous SnO₂ in the shell. At 25 °C, the conductivity of the humidity sensor at 75% relative humidity (RH) was three orders of magnitude larger than that in dry air (5% RH). The response time and recovery time were ∼28 and ∼7 s, respectively, when RH was switched between 5 and 75%. Interestingly, by changing the temperature between 12 and 40 °C at 75% RH, the sensitivity can be tuned between ∼10⁵ (12 °C) and ∼10² (40 °C). Typical thermally switchable properties of β-Ga₂O₃–amorphous-SnO₂ core–shell microribbons at 75% RH were demonstrated using a heating–cooling cycle between 20 and 30 °C. The possible mechanisms have been proposed based on the novel core–shell structures and water adsorption–desorption processes. Our findings pave the way for new types of humidity sensors and thermal switches.