Strain broadening of the dangling-bond resonance at the (111)Si-SiO2interface

It is observed that the linewidth and line shape of the Zeeman resonance associated with dangling bonds at the (111)Si-${\mathrm{SiO}}_2$ interface ($P_b$ centers) vary with the direction of the applied magnetic field. An analysis of the line shape of this resonance indicates that it can be represented analytically by the Voigt function, which is a convolution of Lorentzian and Gaussian line broadening. To a first approximation the Lorentzian component is attributed to natural line broadening and is angle independent. The Gaussian component arises from strain broadening of only $g_{\perp }$ and not $g_{?}$ giving an angle-dependent Gaussian linewidth. The strain broadening of the g→ dyadic is understood in terms of the molecular-orbital theory for the g→ anisotropy of paramagnetic dangling bonds in silicon of Watkins and Corbett. The standard deviation in the bond angle between the paramagnetic dangling bond and the adjacent bonds localized on the common silicon atom is 0.5°, as deduced from our previous measurements of the ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ hyperfine broadening. It is observed at K band that the relative intensity of the $P_b$ resonance, as determined by double numerical integration of the measured derivative spectrum or from integration of the Voigt function, varies from 1 for B∥[111] to approximately 1.7 for B∥[11¯0] with ${\mathrm{B}}_{\mathrm{microwave}\mathrm{\parallel }\left[112\mathrm{¯}\right]}$. .AE