Since the first reports on metastable defects in III-V and II-VI compound semiconductors appeared in the late 1960s, the number of reports on defects with metastable states has been growing at an ever increasing rate. D(X)-center and other metastability defects cause many technical problems that are exacerbated by the uncertainty and controversy surrounding the mechanisms that cause them. A lively mix of theoretical and experimental discussions, D(X)-Centres and other Metastable Defects in Semiconductors presents a timely investigation of these systems. The book discusses topics such as, the validity of negative or positive U models, as well as alternative views that challenge existing ideas. The richness and precision of experimental data now emerging in the field is chronicled as are new investigative techniques. Based on an INT symposium, this book provides a successful forum where an extraordinary variety of ideas, including new perspectives, are examined critically.