This monograph arose out of the recognition of the importance of hydrogen in modern semiconductor technology. Hydrogen is a component of most chemicals used in the fabrication of electronic and photonic devices, is easily incorporated into semiconductors and it is a model impurity for studying defect reactions in solids. While writing this volume we have received a good deal of encourage- ment from our colleagues at AT&T Bell Laboratories, State University of New York at Albany and Lehigh University, and from collaborators at other institutions: to them we extend our sincere appreciation. In...