b-Ga2O3 nanowires and thin films for metal oxide semiconductor gas sensors: Sensing mechanisms and performance enhancement strategies

The reliable, selective, and fast detection of the inorganic and organic gases in indoor and outdoor air and industrial processes is a huge challenge for environmental sustainability, healthier life, and disease control and diagnosis. Metal oxides have been frequently explored as highly sensitive receptor elements in the electronic gas sensors since the 1960s. Gallium oxide (Ga2O3), often recognized as one of the widest-bandgap semiconductors, has shown tremendous potential as the inorganic gas receptor because of its extraordinary chemical and thermal stability, and excellent electronic properties. This article presents a comprehensive reference on the electrical properties, historical developments, detection mechanisms, and gas sensing performance of Ga2O3 nanowires and composite nanostructures. In particular, the relationships between composition, nanostructure, and gas sensing properties of galliumcontaining oxidic nanomaterials such as b-Ga2O3 nanowires, surface-modified Ga2O3, metal-doped Ga2O3 or Ga-doped metal oxides, and Ga2O3/metal oxide composite heterostructures are studied. The applications of Ga2O3 gas sensors are discussed with an emphasis on their practical limitations such as high-temperature operation, power consumption, and miniaturization issues. Finally, future research directions and potential developments are suggested.