Abstract
Many of the most advanced applications of semiconductor quantum dots (QDs) in quantum information technology require a fine control of the QDs' position and confinement potential, which cannot be achieved with conventional growth techniques. Here, a novel and versatile approach for the fabrication of site-controlled QDs is presented. Hydrogen incorporation in GaAsN results in the formation of N-2H and N-2H-H complexes, which neutralize all the effects of N on GaAs, including the N-induced large reduction of the bandgap energy. Starting from a fully hydrogenated GaAs/GaAsN:H/GaAs quantum well, the NH bonds located within the light spot generated by a scanning near-field optical microscope tip are broken, thus obtaining site-controlled GaAsN QDs surrounded by a barrier of GaAsN:H (laterally) and GaAs (above and below). By adjusting the laser power density and exposure time, the optical properties of the QDs can be finely controlled and optimized, tuning the quantum confinement energy over more than 100 meV and resulting in the observation of single-photon emission from both the exciton and biexciton recombinations. This novel fabrication technique reaches a position accuracy <100 nm and it can easily be applied to the realization of more complex nanostructures.
Highlights
Semiconductor quantum dots (QDs) have attracted increasing interest in the last decades. Thanks to their tunable emission energy and to their narrow luminescence linewidth, they may find – and, in some instances, already have found – possible applications in many fields[1,2], from light-emitting devices (e.g. LED and lasers) to biology, from photovoltaics to sensor devices. Owing to their ability to act as sources of non-classical light states, QDs might serve as the main building blocks of several potentially ground-breaking devices, enabling the first practical implementation of quantum information technology[3]
For years, the strategy to deterministically align a photonic crystal cavity to a single QD was based on the fabrication of the cavity after the QD was first located by microscopy techniques[11]
We can consider that in photonic crystal (PhC) cavities the typical spatial full width at half maximum (FWHM) for the field at the antinode is slightly smaller than the lattice constant of the PhC, which in turn is about 0.25λ, where λ is the wavelength in vacuum of the considered cavity mode
Summary
Semiconductor quantum dots (QDs) have attracted increasing interest in the last decades.
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