Spinel ZnGa₂O₄ has received significant attention from researchers due to its wide bandgap and high chemical and thermal stability; hence, paving the way for it to have potential in various applications. This review focuses on its physical, optical, mechanical and electrical properties, contributing to the better understanding of this material. The recent trends for growth techniques and processing in the research and development of ZnGa₂O₄ from bulk crystal growth to thin films are discussed in detail for device performance. This material has excellent properties and is investigated widely in deep-ultraviolet photodetectors, gas sensors and phosphors. In this article, effects of substrate temperature, annealing temperature, oxygen partial pressure and zinc/gallium ratio are discussed for device processing and fabrication. In addition, research progress and future outlooks are also identified.

Spinel ZnGa₂O₄ films were grown on c-plane sapphire substrates at the substrate temperature of 400 °C by radio-frequency magnetron sputtering. Post thermal annealing was employed at the annealing temperature of 700 °C in order to enhance their crystal quality. The effect of thermal annealing on the microstructural and optoelectronic properties of ZnGa₂O₄ films was systematically investigated in various ambiences, such as air, nitrogen, and oxygen. The X-ray diffraction patterns of annealed ZnGa₂O₄ films showed the crystalline structure to have (111) crystallographic planes. Transmission electron micrographs verified that ZnGa₂O₄ film annealed under air ambience possesses a quasi-single-crystalline structure. This ZnGa₂O₄ film annealed under air ambience exhibited a smooth surface, an excellent average transmittance above 82% in the visible region, and a wide bandgap of 5.05 eV. The oxygen vacancies under different annealing ambiences were revealed a substantial impact on the material and photodetector characteristics by X-ray photoelectron spectrum investigations. ZnGa₂O₄ film exhibits optimal performance as a metal-semiconductor-metal photodetector when annealed under air ambience. Under these conditions, ZnGa₂O₄ film exhibits a higher photo/dark current ratio of ~10⁴ order, as well as a high responsivity of 2.53 A/W at the bias of 5 V under an incident optical light of 240 nm. These results demonstrate that quasi-single-crystalline ZnGa₂O₄ films have significant potential in deep-ultraviolet applications.

This paper emphasizes that the furnace pressure, crucible rotation, and pulling rate have important effects on interstitial oxygen (O_i) concentrations and micro-defects during growth in a Czochralski single-crystal silicon (CZ-Si) growth furnace. Since oxygen in a silicon ingot influences minority carrier lifetime, different set-points of furnace pressure and crucible rotation were controlled to achieve different degrees of O_i. The O_i content has a positive correlation with furnace pressure and crucible rotation. Various numbers of micro-defects were generated under the influence of different pulling rates, owing to the transformation from liquid to solid. The sample also underwent Secco etching and a high-temperature wet oxidation to observe defects caused by the O_i concentration and pulling rate, namely, flow pattern defects (FPDs) and oxidation-induced stacking faults (OISFs). Optical microscopy was employed to confirm the surface topography, and for defect number counting, to observe the correlation between the defects and the minority carrier lifetime. The overall results show that the minority carrier lifetime is mainly dominated by OISFs under high O_i content and FPDs under low O_i content. Therefore, growth using a CZ-Si growth furnace should be carried out with low furnace pressure, low crucible rotation, and low pulling rate to reduce micro-defects.

In this study, we prepared various aluminum-doped zinc oxide (AZO) surface structures via chemical bath deposition for use in biomedical sensors. Indium tin oxide (ITO) conductive films were deposited on glass substrates via electron beam evaporation, and AZO nanorods were subsequently grown on the ITO layer using chemical bath deposition at a bath temperature of 90°C. The AZO/ITO sensor electrode was further optimized through furnace annealing, improving its structural and electrical properties. This nanostructure enhances the ability of biomedical sensor films to adsorb H+ and OH^- ions by increasing the reactive surface area between the film and the solution under test, thereby improving pH sensitivity. In addition, we used an extended gate field effect transistor module to measure glucose concentrations ranging from 0 to 10 mg/ml, achieving sensitivity values of 55.4 mV/pH and 8.07 mA/mg*ml^-1. These findings have significant implications for the future development of blood glucose monitoring and microenvironmental sensing systems.