Amorphous Thin Films: Insulators, Metals, and Semiconductors

Amorphous thin films of some materials can be prepared by various deposition techniques onto ambient temperature substrates. The process results in material which resembles the crystalline counterpart in many respects, although they show defect-related electronic states which influence some of their properties. Nonetheless they have been exploited in some technologies. Researchers at Victoria University and Industrial Research Ltd. have worked in the field for many years, and this paper reviews some of that work. The most recent studies have focused on amorphous GaN, a wide bandgap semiconductor, and the review emphasizes this ongoing research. Rapid progress in reducing the density of defect states is being made and a range of structural, conducting, and optical properties are being investigated. The best films so far have unobservable mid-gap absorption and a resistivity of 104 Ω cm.