Extensive and systematic studies on reactive magnetron sputtering of InN thin films are summarized. The films have been deposited onto several types of substrates, with variations in such process parameters as deposition temperature, partial pressures of reactive and inert gases, sputtering power and gas flows. These films have been characterized by measuring their electrical, optical, structural and morphological properties. It has been shown that epitaxial growth of InN occurs on the basal plane of single-crystal (00.1) sapphire and (001) mica substrates and on the (111) face of cubic substrates such as silicon and zirconia.
Two principal problems currently limit the usefulness of thin films of InN. First, although epitaxy can be attained with the proper choice of substrate type and deposition temperature, the resulting film is an agglomerate of epitaxial grains -- not a single crystal. Second, all magnetron sputtered InN films prepared to date have low mobility and high carrier concentration (likely due to nitrogen vacancies). In an attempt to address these problems, experiments on the growth and characterization of sputtered InN films have been carried out and are discussed here with particular emphasis on seeded heteroepitaxial growth and the effects of film deposition temperature.
For example, it was found early that the growth of InN on the bare surface of several crystalline substrates at growth temperatures near 350°C results in a morphological transition that causes a degradation of semiconducting properties. The predeposition of an AIN seed layer inhibits this morphological transition and stabilizes a relatively high mobility state, but a still too high carrier concentration obtains. Further progress critically depends on optimizing the seeded heteroepitaxial growth technique in conjunction with the achievement of InN films with lower density of nitrogen vacancies.