Pinpointing the exact positions of the dots in the material is a challenging task, which could greatly help the characterization and engineering of these devices. In this context, researchers at our laboratory and at Néel Institute developed an original position mapping technique. By generating a controlled and inhomogeneous strain in the photonic structure, one induces a spectral shift of the QD emission, whose magnitude and sign depend on the local strain. Monitoring the QD emission change by optical spectroscopy thus yields the QD position with an accuracy that can be as low as 1 nanometer. This technique was demonstrated on a photonic wire embedding a single sheet of self-assembled QDs (Figure). Material strain was here obtained by the selective excitation of mechanical vibration modes. Combining the results obtained from the excitation of two orthogonal flexural modes, one obtains a map of the QD position in the growth plane. In the future, this approach could be applied to locate QDs embedded in other photonic structures (e.g. micropillar) and could be extended to other quantum emitters which are sensitive to strain.

Caption : (Left) SEM picture of the investigated structure. This photonic trumpet embeds a single sheet of self-assembled quantum dots, located close to its base. (Right) Map of the strain in the quantum dot layer, for a flexion of the trumpet along the horizontal axis. The strain experienced by the emitters strongly depends on their position.