Influence of heterogeneities on the electronic properties of hydrogenated amorphous silicon

Abstract

An attempt is made to highlight the importance of inhomogeneities in hydrogenated amorphous silicon (a-Si:H), in controlling its electronic properties. We note that hydrogen increases the gap in a-Si:H and that hydrogen is distributed inhomogeneously in it. This gives rise to long-range potential fluctuations, which are mostly uncorrelated and usually ignored. These and other such considerations have not only enabled us to gain new insights into the behaviour of a-Si:H in general, but have also allowed us to resolve several unsolved puzzles. Among these are questions like why undoped a-Si:H is n-type, why the creation of dangling bonds upon light soaking (LS) so inefficient, why a-Si:H degrades more upon LS when it is doped, why the reciprocity fails for light-induced degradation, why presence of nanocrystalline silicon improves stability and so on. We provide evidence to support some of our ideas and make suggestions for verifying the others.

Keywords:

• amorphous silicon
• photodegradation
• potential fluctuations
• nanocrystalline silicon
• inhomogeneities

Acknowledgements

The author is grateful to Professor H. Fritzsche for comments and suggestions. Useful discussions with Professors Sushil Auluck, Rajendra Prasad, Dr Rajeev Gupta and Dr Sushil Kumar are acknowledged. Thanks are also due to N.P. Reddy for help with the experiments. The author is an Emeritus Scientist of the Council of Scientific & Industrial Research (CSIR), New Delhi.