Elastic Properties of Thin Film Silicon: Final Report; 1 June 1999--23 August 2002

The original purpose of this research, as stated in the annual reports, was the study of the role of hydrogen in thin (polycrystalline) silicon films. We quote from the 2001 Annual Report:''Thin-film silicon holds great promise as a semiconductor that can be produced economically on a large scale. Its exceptional properties for photovoltaic energy conversion have already been demonstrated and are the subject of intensive study worldwide. Yet the entire field of heterogeneous thin-film silicon (often referred to as polycrystalline silicon) is remarkably poorly understood. This is not too surprising, given our limited understanding of one of its constituents, amorphous silicon, in particular in its hydrogenated form. In the thin-film silicon, the interfaces between crystalline grains and between crystalline and amorphous regions appear to be of particular importance, because they are likely to lead to the exceptionally large optical absorption observed in these films, which exceeds that of both c-Si and a-Si:H. The understanding of the interfacial regions is, however, entirely lacking. What is their fractional volume, and how can it be controlled? Where is the hydrogen located in these films, and what is its role in their electronic properties? A better understanding of these fundamental questions is crucial for the development of better photovoltaic devices and for any other technological application, as well. This is the objective of the present study.