Effect of local strain on single acceptors in Si

We explore the low temperature transport through a resonant acceptor impurity located near a metal-semiconductor interface and observe a large shift (12 meV) and splitting (0.8 meV) of its ground state. The shift is attributed to the quadratic Stark effect resulting from the electric field of the electrostatic barrier. The splitting is too large to be attributed to a linear Stark splitting. We calculate the strain field due to a nearby point defect and show that it can cause a large ground state splitting.