$P_{b1\mathrm{}}$ interface defect in thermal $\mathrm{}\left(100\right)\mathrm{}{\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}\mathrm{O}}_2:$ ${}^{29}\mathrm{Si}$ hyperfine interaction

An optimized electron spin resonance study has resulted in the observation of the full angular dependence of the hyperfine interaction spectrum associated with the unpaired electron of the $P_{b1\mathrm{}}$ point defect at the thermal $\mathrm{}\left(100\right)\mathrm{}{\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}\mathrm{O}}_2$ interface, showing that the dominant interaction arises from a single ${}^{29}\mathrm{Si}$ isotope. The hyperfine tensor exhibits nearly axial (weakly monoclinic I) symmetry with $A_{\parallel }$ $\left(\parallel 〈211〉\right)=167\mathrm{}\pm 3\mathrm{G}$ and $A_{\perp }=107\mathrm{}\pm 4\mathrm{G}.$ Molecular-orbital analysis indicates that the unpaired electron resides for ∼58% in a single unpaired Si hybrid orbital, found to be 14% s like and 86% p like, with the p orbital pointing closely along a 〈211〉 direction at 35.26° with the [100] interface normal. If O is excluded as an immediate part of the defect, the results establish the kernel of the $P_{b1\mathrm{}}$ defect as a tilted (∼22° about 〈01¯1〉) asymmetric, likely strained, ${\mathrm{Si}}_3{\mathrm{\equiv }\mathrm{Si}}_{\mathrm{•}}$ unit. Like $P_b$ and $P_{b0\mathrm{}},$ $P_{b1\mathrm{}}$ is a prototype Si dangling bond defect. All available structural information may, in principle, be compatible with the moiety being incorporated as part of a defected strained Si-Si dimer configuration at slightly subinterfacial position. The dimer has previously been advanced as a natural building block in matching ${\mathrm{SiO}}_2$ to (100)Si.