Investigation on the microscopic structure of E' center in amorphous silicon dioxide by electron paramagnetic resonance spectroscopy

The E′δ center is one of the most important paramagnetic point defects in amorphous silicon dioxide (a-SiO2) primarily for applications in the field of electronics. In fact, its appearance in the gate oxide of metal-oxide-semiconductor (MOS) structures seriously affects the proper work of many devices and, often, causes their definitive failure. In spite of its relevance, until now a definitive microscopic model of this point defect has not been established. In the present work we review our experimental investigation by electron paramagnetic resonance (EPR) on the E′δ center induced in γ-ray irradiated a-SiO2. This study has driven us to the determination of the intensity ratio between the hyperfine doublet and the main resonance line of this point defect. On the basis of this estimation we have pointed out that the unpaired electron wave function of the E′δ center is actually delocalized over four nearly equivalent silicon atoms, shedding new light on the microscopic structure of this technologically relevant point defect.