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As a promising ultra-wide bandgap semiconductor material, gallium oxide (Ga2O3) is attracting an extensive attention of researchers due to its feasible growth process, appropriate bandgap of 4.4-5.3 eV allowing for deep-ultraviolet (deep-UV) detection, good physical and chemical stability, high breakdown field strength and electron mobility, etc. Different from the strict processes for controllable crystalline Ga2O3 (usually refer to stable monoclinic β-Ga2O3), amorphous Ga2O3 (a-Ga2O3) film can be prepared uniformly at low temperature on a large-area deposition substrate, suggesting great advantages such as low manufacturing cost and excellent flexibility, dispensing with high-temperature and high vacuum techniques. Thus, a-Ga2O3 extremely facilitates important applications in various applied fields. Therefore, in this concise review, we summarized several major deposition methods for a-Ga2O3 films, of which the characteristics were discussed. Additionally, potential methods to optimize the film properties were proposed by right of the inspiration from some recent studies. Subsequently, the applications of a-Ga2O3 thin films, e.g., in photodetectors, resistive random access memories (RRAMs) and gas sensors, were represented with a fruitful discussion of their structures and operating mechanisms.

A self-powered solar-blind ultraviolet (UV) photodetector (PD) was successfully constructed on a Ga2O3/Bi2WO6 heterojunction, which was fabricated by spin-coating the hydrothermally grown Bi2WO6 onto MOCVD-grown Ga2O3 film. The results show that a typical type-I heterojunction is formed at the interface of the Ga2O3 film and clustered Bi2WO6, which demonstrates a distinct photovoltaic effect with an open-circuit voltage of 0.18 V under the irradiation of 254 nm UV light. Moreover, the Ga2O3/Bi2WO6 PD displays excellent photodetection performance with an ultra-low dark current of ∼ 6 fA, and a high light-to-dark current ratio (PDCR) of 3.5 × 104 in self-powered mode (0 V), as well as a best responsivity result of 2.21 mA/W in power supply mode (5 V). Furthermore, the PD possesses a stable and fast response speed under different light intensities and voltages. At zero voltage, the PD exhibits a fast rise time of 132 ms and 162 ms, as well as a quick decay time of 69 ms and 522 ms, respectively. In general, the newly attempted Ga2O3/Bi2WO6 heterojunction may become a potential candidate for the realization of self-powered and high-performance UV photodetectors.

A flower-like SnO2–SnO/porous GaN (FSS/PGaN) heterojunction was fabricated for the first time via a facile spraying process, and the whole process also involved hydrothermal preparation of FSS and electrochemical wet etching of GaN, and SnO2–SnO composites with p–n junctions were loaded onto PGaN surface directly applied to H2S sensor. Meanwhile, the excellent transport capability of heterojunction between FSS and PGaN facilitates electron transfer, that is, a response time as short as 65 s and a release time up to 27 s can be achieved merely at 150 °C under 50 ppm H2S concentration, which has laid a reasonable theoretical and experimental foundation for the subsequent PGaN-based heterojunction gas sensor. The lowering working temperature and high sensitivity (23.5 at 200 ppm H2S) are attributed to the structure of PGaN itself and the heterojunction between SnO2–SnO and PGaN. In addition, the as-obtained sensor showed ultra-high test stability. The simple design strategy of FSS/PGaN-based H2S sensor highlights its potential in various applications.

A 4×4 beta-phase gallium oxide (β-Ga2O3) deep-ultraviolet (DUV) rectangular 10-fingers interdigital metal-semiconductor-metal (MSM) photodetector array of high photo responsivity is introduced. The Ga2O3 thin film is prepared through the metalorganic chemical vapor deposition technique, then used to construct the photodetector array via photolithography, lift-off, and ion beam sputtering methods. The one photodetector cell shows dark current of 1.94 pA, photo-to-dark current ratio of 6×107, photo responsivity of 634.15 A⋅W−1, specific detectivity of 5.93×1011 cm⋅Hz1/2⋅W−1 (Jones), external quantum efficiency of 310000%, and linear dynamic region of 108.94 dB, indicating high performances for DUV photo detection. Furthermore, the 16-cell photodetector array displays uniform performances with decent deviation of 19.6% for photo responsivity.