Solidity is an imperfect state

Solid materials are by necessity imperfect systems. Some defects are vital for applications, such as semiconductor doping with selected impurities for conductivity adjustment or for control of carrier lifetimes. Our modern characterization techniques have greatly facilitated observation and parameterization of many defects. Amorphous and nonstoichiometric materials have recently become highly useful and will stimulate more research and development activities in the future. (C) 2007 Elsevier Ltd. All rights reserved.