This book gives a complete overview of the properties of deep-level, localized defects in semiconductors. Such comparatively long-lived (or metastable) defects exhibit complex interactions with the surrounding material, and can significantly affect the performance and stability of certain semiconductor devices. After an introductory discussion of metastable defects, the authors present properties of DX and EL2 centers in IIISHV compounds. They also deal with additional crystalline materials before giving a detailed description of the properties and kinetics of photo-induced defects in amorphous semiconductors. The book closes with an examination of the effects of photo-induced defects in a range of practical applications. The book will be of great use to graduate students and researchers interested in the physics and materials science of semiconductors.