Quantum Sensor For Nanoscale Defect Characterization

The optical and electronic properties of semiconductors are strongly affected by structural and stoichiometric defects. The precise incorporation of dopants and the control of impurities are essentially what makes semiconductors useful materials for a broad range of devices. The standard defect and impurity characterization methods are sensitive only on a macroscopic scale, like the most widely used method of deep-level transient spectroscopy (DLTS). We perform time-resolved measurements of the resonance fluorescence of a single self-assembled (In,Ga)As quantum dot (QD) at low temperatures (4.2 K). By pulsing the applied gate voltage, we are able to selectively occupy and unoccupy individual defects in the vicinity of the dot. We address the exciton transition of the QD with a tunable diode laser. Our time resolved measurements exhibit a shift of the resonance energy of the optical transition. We attribute this to a change of the electric field in the dot?s vicinity, caused by electrons tunneling from a reservoir to the defect sites. Furthermore, we are able to characterize the defects concerning their position and activation energy by modeling our experimental data. Our results thus demonstrate how a quantum dot can be used as a quantum sensor to characterize the position and activation energy of individual shallow defects on the nanoscale.