Review—ZnO-based Thin Film Metal Oxide Semiconductors and Structures: Transistors, Optoelectronic Devices and Future Sustainable Electronics

Metal oxide thin films are critically important materials for modern technologies, particularly semiconductor thin films in transistors and optoelectronic applications. Many metal oxide thin films attract interest for their electronic bandgap, charge carrier mobility, optical opacity, luminescence, low cost, relative abundance, and environmentally-friendly production. Additionally, these properties are often tuneable via particle size, film density, surface morphology, film deposition, growth method, hetero-interface engineering or ion-doping. The n-type semiconducting zinc oxide (ZnO) is an important material, possessing a variety of useful properties including an intrinsically wide direct bandgap, high electron mobility, relatively high exciton binding energy, high optical transparency, demonstrated metal-ion doping, a range of different particle morphologies and deposition methods, electro/photoluminescence, low cost, and a variety of existing green synthesis methods. Here, these aspects of ZnO and some related compound semiconducting oxides are reviewed, focusing on how the unique properties of these metal oxides make them suitable for a range of different applications from thin film transistors, high mobility oxide interfaces, transparent conductive oxides, photoanodes photodetectors, chemical sensors, photocatalysts, superlattice electronics, and more. The properties and deposition methods and their impact on functionality will be discussed alongside their role in sustainable optoelectronics.