E′ centers in silicon dioxide:: First-principles molecular dynamics studies

The point-like defects known as E' centers are the most abundant natural defects in silicon dioxide (SiO2) and have been identified as unpaired sp(3) dangling bonds. Their importance stems from the fact that they deeply affect the quality of electronic and optical devices. For this reason, particular attention has been paid in their characterization since the early 1960s. In this work, we review theoretical and experimental results concerning these kinds of defects, focusing on the related charge and spin states. In particular, the defect known as E' in crystalline quartz and its analogous E'gamma, in amorphous SiO2, detected by electron spin resonance, are shown to be due to the Si dangling bonds that arise either upon removal or displacement of an oxygen atom in a SiO2 network, accompanied by an asymmetric relaxation of the network.