Amorphous oxide semiconductors: From fundamental properties to practical applications

Amorphous oxide semiconductors (AOSs) have exceptional features of high visible transparency, high carrier mobility, excellent uniformity, and low-temperature growth process, making them promising in the electronic and information industry. InGaZnO is the most widely studied AOS and has been applied in commercial, which, however, contains rare and precious indium. For sustainable development, a diversity of In-free AOSs have been designed and proposed, which are attracted more and more attention. There have been several reviews on AOSs mainly centred on InGaZnO; in contrast, the review on In-free AOSs is not available at present. In this work, we provide a comprehensive review on In-free AOSs from fundamental properties to practical applications. Various In-free AOSs available in literatures are introduced, with the focus on ZnSnO-based AOSs. Thin-film transistors (TFTs) based on In-free AOSs are investigated in detail, which are the key device for next-generation transparent and flexible displays. Also, the applications in transparent electrodes, sensors, memristors, synaptic devices, and circuits are introduced. This review is expected to provide a guide to well understand the state-of-the-art principles, materials, devices, fabrication, applications, and perspectives of In-free AOSs.