Lone-Pair Relationships and the Origin of Excited States in Amorphous Chalcogenides
What are the chemical and structural bases of localized states in amorphous materials? In the case of tetrahedral amorphous materials, chemistry and structure can be closely related and the localized states can be clearly distinguished, for example, materials which have not reached their lowest free energy can have dangling bonds, structurally dependent voids and other kinds of vacancy defects. We classify these as extrinsic localized states which can be annealed out. When the materials are at their lowest free energy, as represented by the ideal model of Polk,(1) the localized states which remain and are the result of chemical bonding and positional disorder we consider intrinsic. In such materials, substitutional impurities can insert new extrinsic localized states and the possibility of ordinary doping exists, as shown by the work of Spear and LeComber.(2) While this is an important subject, we believe that it will follow the concepts of classical crystalline tetrahedral materials.
KeywordsLone Pair Amorphous Material Vacancy Defect Lower Free Energy Amorphous Semiconductor
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