Direct observation of dangling bond motion in disordered silicon

We report an unexpected temperature dependence of the electron-spin-resonance linewidth $\Delta H_{\mathrm{PP}}$ for the silicon $D$-center resonance in polycrystalline silicon. Distinct temperature dependences were found in as-prepared and hydrogen-passivated polycrystalline silicon. This observation invalidates the identification of this resonance with a static dangling bond, and changes the perspective on similar $D$-center resonances observed in amorphous silicon, porous silicon, and at crystal silicon interfaces. We propose that motional averaging is the principal mechanism for this effect, and illustrate this view with a calculation based on hopping of the $D$ center.