We demonstrate the deterministic integration of single site-controlled quantum dots (SCQDs) into micropillar cavities. Spatial resonance between single positioned QDs and GaAs/AlAs micropillar cavities was achieved using cross markers for precise SCQD-cavity alignment. Cavity effects are clearly reflected in an enhanced photoluminescence intensity when tuning SCQD emission lines through the fundamental cavity resonance. Single photon emission from a spatially and spectrally coupled SCQD-resonator system is confirmed by photon autocorrelation measurements yielding a g(2)(0) value of 0.12.
Results obtained by an advanced growth of site-controlled quantum dots (SCQDs) on pre-patterned nanoholes and their integration into both photonic resonators and nanoelectronic memories are summarized. A specific technique has been pursued to improve the optical quality of single SCQDs. Quantum dot (QD) layers have been vertically stacked but spectrally detuned for single SCQD studies. Thereby, the average emission linewidth of single QDs could be reduced from 2.3 meV for SCQDs in a first QD layer close to the etched nanoholes down to 600 microeV in the third InAs QD layer. Accurate SCQD nucleation on large QD distances is maintained by vertical strain induced QD coupling throughout the QD stacks. Record narrow linewidths of individual SCQDs down to approximately 110 microeV have been obtained. Experiments performed on coupled photonic SCQD-resonator devices show an enhancement of spontaneous emission. SCQDs have also been integrated deterministically in high electron mobility heterostructures and flash memory operation at room temperature has been observed.
Positioned AlGaAs nanowires with an embedded axial heterostructure GaAs quantum dot (QD) on a prepatterned substrate have been grown. The geometry of the nanowires allows for an outcoupling of the emitted light through the nanowire tip and thereby to probe a single nanowire directly on the growth substrate. Single QD linewidths as small as 95 μeV and photon antibunching were observed at continuous wave laser excitation with a second order autocorrelation function g(2)(0)=0.46. The results represent an attractive bottom-up fabrication approach for the realization of high efficiency photonic wire based single photon sources.
We report on a scalable fabrication technology for devices based on single quantum dots (QDs) which combines site-controlled growth of QDs with an accurate alignment procedure. Placement of individual QDs and corresponding device structures with a standard deviation of around 50nm from the target position was achieved. The potential of the technology is demonstrated by fabricating arrays of mesas, each containing one QD at a defined position. The presence of single, optically active QDs in the mesas was probed by scanning microphotoluminescence of the mesa arrays.
We present narrow spectral linewidth from single site-controlled In(Ga)As quantum dots (QDs) grown on nanoholes, which were defined by electron beam lithography on a (100) GaAs substrate. The long-range ordering of uncapped QDs is confirmed by electron microscopy whereas the ordering of capped QDs is visualized by atomic force microscopy. We find a small inhomogeneous broadening of 14.4 meV for the ensemble emission of site-controlled QDs with 300 nm lattice period. The photoluminescence from the excitonic transitions of single site-controlled QDs exhibits linewidth values down to 43 μeV, which is promising for the investigation of pronounced cavity quantum electrodynamic effects in scalable QD-microresonator systems.
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