InN, a historic review: from obscurity to controversy

In the last two years the semiconducting material indium nitride has come into intense investigation. The development of new generations of nitride based devices are incumbent upon a better understanding of indium nitride and its alloys with gallium nitride. This review takes a timely look at the older literature for this material in relation to latest research. Controversy surrounds the material in terms of its band-gap, the electron effective mass, the defect properties, the role of oxygen, and the variation of the decomposition temperature. Some of the older literature has already addressed these problems, in particular a working model of oxygen in indium nitride has been in place for many years. The variation of the decomposition temperature with an overpressure of ions has been addressed. While the Moss-Burstein effect for InN has had a long history of study. The latest developments in our understanding of the properties of InN are also reviewed here including an overview of work presented at the recent First International Workshop on InN. The issue of the band-gap has been re-opened with strong evidence that the 0.7 eV feature is due to a deep level defect related to indium rich aggregates. Preliminary work indicates a band-gap in the range of 1.0 to 1.5 eV is likely, though the old band-gap of 1.89 eV cannot at this stage be excluded. The carrier concentration dependence of the free electron effective mass is discussed, as is the appropriateness of using the Kane model for the band structure of InN. The problems of film stoichiometry and uniformity are also addressed.