Single Site-controlled Quantum Dots Research Articles

Enhancing the photon-extraction efficiency of site-controlled quantum dots by deterministically fabricated microlenses

We report on the realization of scalable single-photon sources (SPSs) based on single site-controlled quantum dots (SCQDs) and deterministically fabricated microlenses. The fabrication process comprises the buried-stressor growth technique complemented with low-temperature in-situ electron-beam lithography for the integration of SCQDs into microlens structures with high yield and high alignment accuracy. The microlens-approach leads to a broadband enhancement of the photon-extraction efficiency of up to (21 ± 2)% and a high suppression of multi-photon events with g(2)(τ = 0) < 0.06 without background subtraction. The demonstrated combination of site-controlled growth of QDs and in-situ electron-beam lithography is relevant for arrays of efficient SPSs which, can be applied in photonic quantum circuits and advanced quantum computation schemes.

Size-dependent properties of single InAs quantum dots grown in nanoimprint lithography patterned GaAs pits

We report on the structural and optical properties of single InAs quantum dots (QDs) formed in etched GaAs pits with different dimensions. The site-controlled QDs were fabricated by molecular beam epitaxy on GaAs(001) surfaces patterned by nanoimprint lithography. We show that the properties of the QDs can be modified by varying the dimensions of the etched GaAs pits. Increasing the pit size resulted in larger QDs and thus in longer photoluminescence wavelengths. However, the fine structure splitting remained unaffected. A photoluminescence linewidth of 41 μeV and average fine structure splitting of 15.7 μeV were obtained for exciton recombination in the single site-controlled QDs.

In(Ga)As/GaAs site‐controlled quantum dots with tailored morphology and high optical quality

AbstractIn this article, we describe epitaxial growth and investigations of optical properties of In(Ga)As/GaAs site‐controlled quantum dots (QDs) fabricated on (001)‐oriented GaAs substrates. The QD nucleation is directed by pre‐patterning planar GaAs surfaces with shallow nanoholes. The focus of this work lies on the realization of arrays of site‐controlled QDs (SCQDs) with a tailored morphology and optical properties comparable to QDs fabricated on planar substrates. By maximizing the migration length during QD deposition, we were able to increase the QD pitches to values exceeding device dimensions of typical semiconductor microresonators. The introduction of a seeding layer in our growth scheme allows us to extend the vertical distance between the QDs and the etched nucleation centres to about 20 nm without suffering from nanoholes being occupied by multiple QDs. Furthermore, the extended distance between the QD layer and the re‐growth interface allows us to preserve excellent optical properties of the single QDs as probed in photoluminescence with an average single QD related linewidth of 133 µeV and minimum values as low as 25 µeV for non‐resonant excitation. The high yield of optically active QDs on the pre‐defined nucleation positions is studied by cathodoluminescence (CL) with high spatial resolution. We find emission from single SCQDs on more than 90% of the nucleation centres, which is a pre‐requisite for any scalable QD‐device fabrication scheme.

Microcavity enhanced single photon emission from an electrically driven site-controlled quantum dot

In this work we report on the integration of single site-controlled quantum dots (SCQDs) into electrically driven micropillar cavities. The electroluminescence of these devices features emission of single SCQDs with inhomogeneous broadenings down to 170 µeV. The enhancement of electroluminescence by quantum dot-cavity coupling is demonstrated by temperature dependent investigations. Single photon emission from a spatially and spectrally coupled SCQD-resonator system is confirmed by photon autocorrelation measurements under electrical excitation yielding a g(2)(0) value of 0.42.

Single photon emission from a site-controlled quantum dot-micropillar cavity system

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.