A gas sensor based on a ZnGa 2 O 4 (ZGO) thin film grown by metalorganic chemical vapor deposition operated under the different temperature from 25 °C to 300 °C is investigated in this study. This sensor shows great sensing properties at 300 °C. The sensitivity of this sensor is 22.21 as exposed to 6.25 ppm of NO and its response time is 57 s. Besides that, the sensitivities are 1.18, 1.27, 1.06, and 1.00 when exposed to NO 2 (500 ppb), SO 2 (125 ppm), CO (125 ppm), and CO 2 (1500 ppm), respectively. These results imply that the ZGO gas sensor not only has high sensitivity, but also has great selectivity for NO gas. Moreover, the obtained results suggest that ZGO sensors are suitable for the internet of things(IOT) applications.

Deep ultraviolet (DUV) phototransistors with high photoresponsivity are fabricated on ZnGa 2 O 4 grown by metal−organic chemical-vapor deposition. Owing to transistor actions, the photodetector meets to a large photocurrent and optical response. When illuminated with photon wavelength within the range of 200−250 nm, the ZnGa 2 O 4 -based phototransistor presented a large responsivity, especially 1.51 × 10 6 A/W as the incident light at 210 nm with 1.73 μW/cm 2 . It was also observed that the photocurrent/dark current ratio and rising time can be improved by gate control, which is related to threshold voltage shifting when under illumination. These results demonstrate ZnGa 2 O 4 -based phototransistor is a very promising candidate for DUV optoelectronic devices applications.

The development of phototransistors is attributed to material stability, and energy saving has remained a challenge. This is particularly important for single-crystalline ZnGa 2 O 4 epitaxial thin films essential for applications in sensing, energy conversion, and storage. We report herein that high-temperature thermal annealing with 800 °C in N 2 ambient for 1 h could significantly improve epilayer quality, which has been used to fabricate the phototransistor. It was found that the off current of the annealed sample decreased to be ∼2 pA and I DS induced by the visible current (at 450 nm) response can be reduced from 2 × 10 −8 to 3 × 10 −9 A as compared with that of the asgrown phototransistor. It could have resulted from the higher crystallinity and lower defect density after the annealing treatment. The responsivity of a ZnGa 2 O 4 phototransistor is 4.74 × 10 2 A/W at 240 nm, in which the rejection ratio is improved to 1.54 × 10 2 . Moreover, the resulting ZnGa 2 O 4 phototransistor has an excellent 0.4 s response time. The above results demonstrate that the high superiority of annealed ZnGa 2 O 4 can be applied in the deep ultraviolet photodevices.

The properties of gas sensors based on Ga-doped ZnO epilayers grown by metalorganic chemical vapor deposition with dislocation and strain control inside the active layer have been investigated. The gas sensor device based on a Ga-doped ZnO epilayer with a lower TEGa flow rate presents better performance for NO sensitivity than based on a Ga-doped ZnO epilayer with higher TEGa flow. It could be due to Ga source deficiency during the film formation, which results in the higher dislocation density in the ZnO epilayer. In our devices, the best performing device has a NO sensitivity of 23.653 under a 2.5 ppm NO environment. Furthermore, the sensitivities are 5.321, 1.692, 3.320, 1.000, 1.066, and 1.163 for our device with the atmosphere of NO (500 ppb), NO2 (500 ppb), CO (100 ppm), CO2 (1500 ppb), SO2 (100 ppm), and NH3 (100 ppm), respectively. In this work, the stain of the activated film is quantified by high-resolution lattice images, and the higher strain value sample performs better NO sensitivity than others. The result is correlated to the amount of dangling bond inside the activated layer and highly relevant to a proposed strain quantification method. Finally, our device still has a sensitivity as a NO gas concentration lowers to 25 ppb, which is promising for future medical applications.

Single-crystalline ZnGa2O4 epilayers with different diethylzinc (DEZn) flow rates were successfully grown on sapphire substrates. By decreasing the DEZn flow rate and keeping the deposition time constant, the operational mode of the transistors changed from depletion mode (D-mode) to enhancement mode (E-mode). The relevant electrical properties and physical characteristics are well presented and verified. An E-mode (DEZn = 10 sccm) n-channel thin-film transistor was fabricated for deep-ultraviolet (DUV) phototransistor application. In the phototransistor, the photocurrent gain values increased substantially in the DUV region, the peak value of which measures 1.54 × 102 at 240 nm. The superior performance of DUV phototransistors is correlated to the improvement in the quality of materials.