Electron trapping in SiO2 - An injection mode dependent phenomenon

Electron trapping in MOS structures and its dependence on the injected electron energy distribution and oxide field were studied. It is found that in high injection level´s trapping efficiency and saturation level increase with the accelerating field in the Si, and decrease with increase in the oxide field. These results differ markedly from those obtained in low level injection, in which it is assumed that trapping is of electrons injected from the Si into the oxide conduction band. Based on the high level injection experimental results, it is proposed that significant electron trapping is obtained through direct tunneling of hot electrons with energy less than the potential barrier, into the localized states in the oxide near Si-SiO2interface. Confirmation of the location of the trapped electrons is obtained from detrapping measurements and the boron doping concentration effect on trapping.