Post-thermal-Induced Recrystallization in GaAs/Al_0.3Ga_0.7As Quantum Dots Grown by Droplet Epitaxy with Near-Unity Stoichiometry

Abstract

Here, we investigate the stoichiometry control of GaAs/Al 0.3 Ga 0.7 As droplet epitaxy (DE) quantum dots (QDs). Few tens of core nonstoichiometries in the Ga(As) atomic percent are revealed in as-grown “strain-free” QDs using state-of-the-art atomic-scale energy-dispersive X-ray spectroscopy based on transmission electron microscopy. Precise systematic analyses demonstrate a successful quenching of the nonstoichiometry below 2%. The control of the chemical reactions with well-controlled ex situ annealing sheds light on the engineering of a novel single-photon source of strain-free DE QDs free of defects.

Comparative Chemico-Physical Analyses of Strain-Free GaAs/Al0.3Ga0.7As Quantum Dots Grown by Droplet Epitaxy

“…In a finite-difference scheme, we evaluated the Coulomb energy J projected onto the exciton state using the integral [ 32 ] , for the dielectric screening at a given position with spin . The material parameters used in this calculation can be found in the literatures [ 11 , 35 ].…”

“…However, precise QD engineering (e.g., 3D geometric and compositional profiles) is required to sustain such a high capability of quantum networking. Several investigations have reported the fabrication of strain-free QDs using droplet epitaxy (DE) [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ] and by nanohole etching and infilling [ 15 , 16 , 17 , 18 , 19 ]. In the DE mode, QDs such as GaAs are crystallized by diffusing the initial liquid Ga droplets under an As flux, which avoids strain accumulation.…”

“…Strain-free DE QDs can be implemented on an optical chip containing controlled shapes and sizes [ 4 , 10 , 12 , 14 , 20 , 21 ], thereby serving as high-fidelity sources of entangled photons [ 4 , 5 , 22 , 23 ]. However, low-level Al defects and Al intermixing have been probed to remain in strain-free GaAs DE QDs [ 11 , 13 , 24 ]. Atomic scale analyses have confirmed a low degree of Al defects in two-dimensional (2D) [ 11 , 25 ] and 3D composition profiles [ 13 ].…”

“…However, low-level Al defects and Al intermixing have been probed to remain in strain-free GaAs DE QDs [ 11 , 13 , 24 ]. Atomic scale analyses have confirmed a low degree of Al defects in two-dimensional (2D) [ 11 , 25 ] and 3D composition profiles [ 13 ]. These Al remnants modify the electronic and phononic band structures of the GaAs DE QDs, degrading the fidelity of the entangled photons.…”

Strain-induced control of a pillar cavity-GaAs single quantum dot photon source

“…Such a change in the confinement potential not only increases the electron–hole sub-band confinement energies, but also alters the strength of the electron–hole Coulomb interaction. Even small intrinsic strains in GaAs/AlGaAs QDs can significantly alter the quantum confinement parameters 15 .…”