Single-Electron Capacitance Spectroscopy of Individual Dopants in Silicon

Motivated by recent transport experiments and proposed atomic-scale semiconductor devices, we present measurements that extend the reach of scanned-probe methods to discern the properties of individual dopants tens of nanometers below the surface of a silicon sample. Using a capacitance-based approach, we have both spatially resolved individual subsurface boron acceptors and spectroscopically detected single holes entering and leaving these minute systems of atoms. A resonance identified as the B $^{+}$ state is shown to shift in energy from acceptor to acceptor. The resonance is absent in a control sample that does not contain the boron acceptors. By directly measuring the quantum levels and testing the effect of dopant-dopant interactions, this method represents a valuable tool for the development of future atomic-scale semiconductor devices.