Structural and optical properties of position-retrievable low-density GaAs droplet epitaxial quantum dots for application to single photon sources with plasmonic optical coupling

Abstract

The position of a single GaAs quantum dot (QD), which is optically active, grown by low-density droplet epitaxy (DE) (approximately 4 QDs/μm2), was directly observed on the surface of a 45-nm-thick Al0.3Ga0.7As capping layer. The thin thickness of AlGaAs capping layer is useful for single photon sources with plasmonic optical coupling. A micro-photoluminescence for GaAs DE QDs has shown exciton/biexciton behavior in the range of 1.654 to 1.657 eV. The direct observation of positions of low-density GaAs DE QDs would be advantageous for mass fabrication of devices that use a single QD, such as single photon sources.

Post-thermal-Induced Recrystallization in GaAs/Al0.3Ga0.7As Quantum Dots Grown by Droplet Epitaxy with Near-Unity Stoichiometry

“…A detailed description of the growth mechanism and parameters can be found in our previous works. 22,23 We note that the structural morphology and optical characteristics have also been reported for the similar type of DE QDs. 24…”

“…The average QD density of ∼3/μm 2 was obtained by measuring the images of a charge-coupled device for optically excited samples. A detailed description of the growth mechanism and parameters can be found in our previous works. , We note that the structural morphology and optical characteristics have also been reported for the similar type of DE QDs …”

“…The GaAs QDs under investigation were grown by DE using molecular beam epitaxy. − As illustrated in Figure , the epitaxial growth of GaAs QDs in the DE mode is based on the crystallization of Ga droplets via the injection of an As 4 flux. The crystallized GaAs QDs are then capped with an AlGaAs protective layer.…”

“…Experiencing a substantial (intrinsic) strain field, the chemical composition profiles of SK QDs unfortunately significantly modify their optoelectronic properties, which is an obstacle to the integration of QD single-photon sources in on-chip optical circuits. For decades, droplet epitaxy (DE) has attracted attention as an alternative technique for fabricating deterministic QD structural morphologies that are free of strain. − In the DE mode, liquid droplets of a metallic material (Ga) are formed on a group-III-terminated surface, followed by crystallization under the flux of a group-V element (As) (Figure a). While the structural morphology of QDs can be precisely controlled by growth parameters, such as the substrate temperature, the flux of As 4 , and the surface stoichiometry, the DE technique enables the fabrication of “strain-free” GaAs QDs on a lattice-matched AlGaAs matrix.…”

“…The presence of a small amount of defects in DE QDs, however, can strongly modify their optoelectronic properties and their chemi-physical nature, drastically decreasing the efficiency of photon emitters. Suffering from the low efficiency of optical emission in QD photoluminescence (PL), many studies have reported improving the quality of DE QDs by performing ex situ thermal treatments. − ,,,,− The optimization of the post-thermal process (relative to improving the crystallinity of QDs) relies on phenomenological enhancements in the intensity of the QD PL. Such analyses need to be put in structural and chemical contexts that nanoscopic studies have been lacking. − Atomic-resolution systematic analyses of such DE QDs are therefore in high demand to acquire a precise chemi-physical understanding to engineer defect-free and strain-free QDs.…”