Photonic Jet Writing of Quantum Dots Self‐Aligned to Dielectric Microspheres

Abstract

Owing to their ability to generate non‐classical light states, quantum dots (QDs) are very promising candidates for the large‐scale implementation of quantum information technologies. However, the high photon collection efficiency demanded by these technologies may be impossible to reach for “standalone” semiconductor QDs, embedded in a high‐refractive index medium. In this work a novel laser writing technique is presented, enabling the direct fabrication of a QD self‐aligned—with a precision of ±30 nm—to a dielectric microsphere. The presence of the microsphere leads to an enhancement of the QD luminescence collection by a factor 7.3 ± 0.7 when an objective with 0.7 numerical aperture is employed. This technique exploits the possibility of breaking the N−H bonds in GaAs1−xNx:H by a laser light, obtaining a lower‐bandgap material, GaAs1−xNx. The microsphere, deposited on top of a GaAs1−xNx:H/GaAs quantum well, is used to generate a photonic nanojet, which removes hydrogen exactly below the microsphere, creating a GaAs1−xNx QD at a predefined distance from the sample surface. Second‐order autocorrelation measurements confirm the ability of the QDs obtained with this technique to emit single photons.

Selective Effects of the Host Matrix in Hydrogenated InGaAsN Alloys: Toward an Integrated Matrix/Defect Engineering Paradigm

“…Upon hydrogenation these annealed regions would be lower‐energy gap areas, wherein carriers could be laterally confined. In principle, the size of these carrier‐confining potentials could be pushed to the nanoscale by applying the subwavelength light‐focusing techniques recently applied to the fabrication of site‐controlled GaAsN:H/GaAsN quantum dots, [ 10,11 ] thus demonstrating the potential of the novel approach proposed here.…”

“…[1,[4][5][6][7][8] In GaAs 1−x N x , H fully neutralizes the effects of N. This phenomenon was exploited for the realization of single-photon emitters using a spatially selective hydrogen incorporation/removal at the sub-micrometer scale, which permitted a spatial tuning of the energy gap. [9][10][11] This approach would be even more interesting in In y Ga 1−y As 1−x N x , whose band gap energy may be brought in the telecommunication wavelength range. [12] However, indications of an uncertain N passivation in hydrogenated InAs 1−x N x [13][14][15] have prompted the need to understand the conditions that may favor or not such passivation in In y Ga 1−y As 1−x N x alloys, where the local N environment ranges from 4Ga-N clusters (encountered in GaAsN) to 4In-N clusters (as it occurs in InAsN).…”

Optical Trapping, Sensing, and Imaging by Photonic Nanojets

“…The optical properties of the photonic nanojets [65], whispering gallery mode [66], and directional antenna [67] of the microsphere lens enhance the interaction between photons and matter, thereby improving the ability of optical trapping, sensing, and imaging. The imaging of a conventional optical microscope comprises light spots formed by light and dark streaks.…”

Photonic Jets and Single‐Photon Emitters

“…A photonic jet (PJ) consists of a highly intense electromagnetic beam with sub-wavelength lateral extent, obtained by illuminating a micrometer-sized object or microparticle with a plane or Gaussian wave. PJs have been observed with a multitude of particle shapes, including microcylinders, [1,2] microspheres, [3][4][5] micro-ellipsoids, [6,7] micro-cubes, [8] core-shell microspheres, [9,10] and others. [11][12][13][14][15] The lateral size of a PJ can be as small as λ/3, [3] and it can propagate for several wavelengths in the surrounding medium in an elongated shape with little divergence.…”