The Stark splitting of a single fourfold degenerate impurity located within the built-in potential of a metal-semiconductor contact is investigated using low temperature transport measurements. A model is developed and used to analyze transport as a function of temperature, bias voltage, and magnetic field. Our data is consistent with a boron impurity. We report $g$ factors of $g_{1/2}=1.14$ and $g_{3/2}=1.72$ and a linear Stark splitting $2\Delta$ of 0.1 meV.

• Received 22 March 2006

DOI:https://doi.org/10.1103/PhysRevLett.98.096805