Preface

Summary

This book describes the material properties and physical phenomena of hydrogenated amorphous silicon (a-Si:H). It covers the growth of material, the atomic structure, the electronic and optical properties, as well as devices and device applications. Since it focusses on the specific properties of one amorphous material, there is a considerable emphasis on describing and interpreting the experimental information. Familiarity with semiconductor physics is assumed, and the reader is also referred to the excellent books by Mott and Davis, Elliott, and Zallen for further information about the general properties of amorphous semiconductors and glasses.

Research into amorphous semiconductors is directed towards an understanding of how the structural disorder leads to their unique properties. A-Si:H has sometimes been regarded as a derivative of crystalline silicon, in which the disorder simply degrades the electronic properties. Much of the interest in a-Si: H comes from the realization that this is not an accurate view. The disordered atomic structure and the presence of hydrogen combine to give new phenomena which are strikingly different from those in the crystalline semiconductors. The structural disorder results in the localized band tail states characteristic of amorphous materials, which are reflected in the optical, transport and recombination properties, while the hydrogen gives unique defect, doping and metastability effects.

The development of a new material with useful technological applications is relatively rare. Hydrogenated amorphous silicon is gaining increasing use in photovoltaic solar cells and in large area arrays of electronic devices.