Gallium Oxide for Gas Sensor Applications: A Comprehensive Review.

GaO has emerged as a promising ultrawide bandgap semiconductor for numerous device applications owing to its excellent material properties. In this paper, we present a comprehensive review on major advances achieved over the past thirty years in the field of GaO-based gas sensors. We begin with a brief introduction of the polymorphs and basic electric properties of GaO. Next, we provide an overview of the typical preparation methods for the fabrication of GaO-sensing material developed so far. Then, we will concentrate our discussion on the state-of-the-art GaO-based gas sensor devices and put an emphasis on seven sophisticated strategies to improve their gas-sensing performance in terms of material engineering and device optimization. Finally, we give some concluding remarks and put forward some suggestions, including (i) construction of hybrid structures with two-dimensional materials and organic polymers, (ii) combination with density functional theoretical calculations and machine learning, and (iii) development of optical sensors using the characteristic optical spectra for the future development of novel GaO-based gas sensors.