Geometry of epitaxial GaAs/(Al,Ga)As quantum dots as seen by excitonic spectroscopy

Abstract

It is shown that exciton and multi-exciton emission lines ("spectral barcode") of a quantum dot conceal nontrivial structural information on the shape and size of the dot, information which can be uncovered by comparison with atomistic many-body theory. Application to the newly-established strain-free GaAs quantum dots grown via "droplet epitaxy" onto AlGaAs matrix reveal the shape and size as "seen" by spectroscopy. The results show that the previously determined dot height (∼ 14 nm) as "seen" by cross-sectional scanning tunneling microscopy (XSTM) could not possibly be consistent with the excitonic signature (1.7-1.9 eV), as the latter must reflect a 1-4 nm tall dot. Multi-exciton "barcode" and fine structure spitting suggest GaAs/AlGaAs dots are in Gaussianshape in agreement with XSTM measurement. Both spectroscopy and XSTM measurements were done on GaAs dots capped by the Al0.3Ga0.7As barrier layer. The fact that XSTM sees tall dots and spectroscopy sees short dots is thus not because the dot change its height in one experiment relative to the other, but because different dots must have been used. This was uncovered by theoretical simulation of the experiment showing that the two experiments could not possibly correspond to the same dot.

Precise shape engineering of epitaxial quantum dots by growth kinetics

“…Although it is based on the simple mechanism of controlled diffusion during crystallization, the DE-QD shape engineering mechanism is extremely powerful. It permits the independent achievement of usually incompatible targets, namely QD emission; interband, intervalley, spin-orbit, and strain-induced state coupling [4,5]; and electron-phonon scattering [62].…”

“…Both their single-particle and many-particle characteristics depend in a nontrivial way on the QD size and shape [2,3]. This reflects not only simple quantum-confinement physics, but also electronicstructure effects such as interband, intervalley, spin-orbit, and strain-induced state coupling [4,5], as well as electronphonon scattering probability [6][7][8]. The QD shape allows for the engineering of the QD electronic states in order to effectively extend the performance of various optoelectronic devices [9], ranging from room-temperature QD-based intersubband detectors [10] and lasers [11] to semiconductor optical amplifiers [12], polarization-controlled single-photon emitters for quantum communication systems [13,14], and QD-based photovoltaic cells [15][16][17].…”

Excitonic fine structure and binding energies of excitonic complexes in single InAs quantum dashes

“…Using atomistic theoretical calculations for deriving excitonic recombination energies that are available experimentally by means of optical measurements, the assessment to the basic structural information has been performed. 33,45 Additionally, for highly disordered structures the lattice randomness methodology has been examined in order to explain variations in the ordering of the emission spectra within a quantum dot ensemble. 46 Hereby, we investigated single QDashes both experimentally, using microphotoluminescence, and theoretically by atomistic tight-binding theory combined with the configuration interaction method.…”

Magnetic field induced valence band mixing in [111] grown semiconductor quantum dots

“…[8][9][10][11] Such a low, C 2v point symmetry is also relevant for the [001]-grown quantum dots with circular or square-shaped base provided that the top and bottom interfaces are non-equivalent or if an in-plane strain is present. 7,[12][13][14] A promising, alternative approach to suppress the fine structure splitting of the neutral exciton is the growth along the [111] crystal axis, which is also the orientation of most nanowires. 15 This growth axis has the advantage of providing in principle quantum-dot shape of the higher C 3v point symmetry.…”