  We study the coupling of Pb0 dangling bond defects at the Si/SiO2 interface
and 31P donors in an epitaxial layer directly underneath using electrically
detected double electron-electron resonance (EDDEER). An exponential decay of
the EDDEER signal is observed, which is attributed to a broad distribution of
exchange coupling strengths J/2pi from 25 kHz to 3 MHz. Comparison of the
experimental data with a numerical simulation of the exchange coupling shows
that this range of coupling strengths corresponds to 31P-Pb0 distances ranging
from 14 nm to 20 nm.
