Trends in Charged Defect Behavior

Abstract

This chapter summarizes broad generalizations in defect behavior that operate across several classes of semiconductor materials and across surfaces vs. bulk. For example, the defect types that exist in III-V and oxide semiconductors can be predicted with surprising accuracy based on the ambient partial pressures of the volatile constituents of the solid. However, several of these trends have apparently not been previously identified. Crystal properties such as lattice structure and size, as well as the coordination, ionicity, and radii of the constituent atoms inhibit the formation of certain types of defects. When comparing the magnitude and direction of defect-induced relaxations, trends related to ionicity and electron-lattice coupling are observed. For a given material, surface defects do not typically take on the same configurations or range of stable charge states as their counterparts in the bulk. Only modest correspondence exists between the stable charge states of isolated point defects and the corresponding defect associates. At a given Fermi energy, the charge state of a defect associate does not necessarily equal the sum of the charges of the constituent defects. Although the formation energies, symmetry-lowering relaxations, and diffusion mechanisms of bulk and surface defect structures often depend strongly on charge state, typically those effects cannot be predicted a priori.