Effects of excess electron-hole pairs on defect migration in semiconductors

Irradiation of semiconductors by various sources, including X-rays, lasers, and ion strikes, leads to the generation of large concentrations of free electrons and holes. Wide-band-gap, compound semiconductors are often used in power electronics where large voltages are applied to devices. However, the combination of energetic-heavy-ion irradiation and large electric fields may lead to catastrophic device failure (i.e., burnout). The role of defects in such failures is generally an open question. Typically, modification of the defect diffusion barrier by an electric field follows ?E_migr = Eqd for a field of strength E applied to a defect in charge state q, with d being half a hopping length. In this work, using density-functional theory, we investigate the role of significant concentrations of free electrons and holes in modifying the migration barriers. We find that the presence of defect-induced electronic resonances in either the conduction or valence bands can have a significant impact. A number of related issues, results, and connections to experimental data will be discussed.