⋅Si≡${\mathrm{Si}}_3$ defect at thermally grown (111)Si/${\mathrm{Si}}_3$${\mathrm{N}}_4$ interfaces

Electron-spin resonance on various dehydrogenated (111)Si/(oxy)nitride structures, thermally grown at 1000–1150 °C in ${\mathrm{NH}}_3$, reveals the presence of two defects. The major one, called ${\mathit{P}}_{\mathit{b}\mathit{N}}$, is identified as a Si dangling bond (⋅Si≡${\mathrm{Si}}_3$) at the (111)Si/nitride interface aligned perpendicular to the interface; x-ray photoelectron spectroscopy actually shows that the in situ removal of the native Si oxide prior to nitridation is a prerequisite to obtaining stoichiometric ${\mathrm{Si}}_3$ ${\mathrm{N}}_4$ films. The identification is based on strong similarities with the ${\mathit{P}}_{\mathit{b}}$ defect at the (111)Si/${\mathrm{SiO}}_2$ interface, such as the g matrix, the location at the interface, and linewidth anisotropy. This observation of the ⋅Si≡${\mathrm{Si}}_3$ defect at a natural Si/solid interface other than the Si/${\mathrm{SiO}}_2$ one confirms ${\mathit{P}}_{\mathit{b}}$ as a prototype dangling-bond center, its salient properties being set by the underside Si matrix—not by the overlaying insulator. Yet, secondary ESR signatures do differ as the large interface strain, resulting from the greater rigidity of the (oxy)nitrides as compared to ${\mathrm{SiO}}_2$ films, causes a slight perturbation of the ${\mathit{P}}_{\mathit{b}\left(\mathit{N}\right)}$ symmetry, thereby lifting its ${\mathrm{C}}_{3\mathit{v}}$ symmetry. This is born out at 4.3 K by specific distortions of the ${\mathit{P}}_{\mathit{b}\mathit{N}}$ line shape. Upon increasing temperature, the perturbation of the defect’s symmetry is smoothed due to thermally activated averaging over the various defect distortions. The properties of the ${\mathit{P}}_{\mathit{b}}$ and ${\mathit{P}}_{\mathit{b}\mathit{N}}$ defects at higher temperatures become largely identical. Comparison of the extracted unresolved ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ ${\mathit{P}}_{\mathit{b}\mathit{N}}$ and ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ ${\mathit{P}}_{\mathit{b}}$ hf broadenings shows that their relative strengths comply with the known isotopic properties.