ABSTRACT
Perfect crystals exist only in theory or in textbooks. In reality, all crystals have imperfections. Some of these imperfections make semiconductors highly interesting from electrical and optical device points of view. These are the electrically active dopant impurities that either replace a crystal host atom (substitutional) or occupy an interstitial site. Other imperfections are undesirable because they can produce energy levels in the band gap that influence device performance in a detrimental way. Defects are broadly defined as any perturbations in an otherwise perfect crystal. In
this chapter, we discuss ways to classify and understand different types of defects in semiconductors. First, they can be classified by their atomic structure and symmetry. Second, defects are classified by the energy levels that they introduce into the band gap. We then discuss specific defect systems, in order of increasing dimensionality: point defects (impurities and intrinsic defects), line defects (dislocations), and area defects (surfaces and interfaces).
