Dipolar interactions between dangling bonds at the (111) Si-SiO2interface

In this paper a computational model is developed which allows one to calculate the contribution to the Zeeman linewidth arising from magnetic dipole-dipole interactions between unpaired electrons in the dilute limit, which in our specific application correspond to dangling bonds ($P_b$ centers) localized at the (111) Si-${\mathrm{SiO}}_2$ interface. Transmission-electron-microscopy studies of the samples we studied with electron paramagnetic resonance (EPR) indicate that the interface between the silicon and the thermally grown oxide was chemically abrupt and atomically flat over distances ranging from 15 to 300 Å. The atomic flatness of the silicon ‘‘surface’’ at the interface was interrupted by steps from one atomic (111) silicon plane to the next. Thus, the dangling bonds observed by EPR are believed to be essentially localized on a two-dimensional plane. The density of dangling bonds is between 3×${10}^{12}$ and 5×${10}^{12}$ ${\mathrm{cm}}^{\mathrm{-}2}$, which suggests that resolved fine structure might be detectable as well as broadening of the $P_b$ Zeeman resonance.