  Strain-free GaAs/AlGaAs semiconductor quantum dots (QDs) grown by droplet
etching and nanohole infilling (DENI) are highly promising candidates for the
on-demand generation of indistinguishable and entangled photon sources. The
spectroscopic fingerprint and quantum optical properties of QDs are
significantly influenced by their morphology. The effects of nanohole geometry
and infilled material on the exciton binding energies and fine structure
splitting are well understood. However, a comprehensive understanding of
GaAs/AlGaAs QD morphology remains elusive. To address this, we employ
high-resolution scanning transmission electron microscopy (STEM) and reverse
engineering through selective chemical etching and atomic force microscopy
(AFM). Cross-sectional STEM of uncapped QDs reveals an inverted conical
nanohole with Al-rich sidewalls and defect-free interfaces. Subsequent
selective chemical etching and AFM measurements further reveal asymmetries in
element distribution. This study enhances the understanding of DENI QD
morphology and provides a fundamental three-dimensional structural model for
simulating and optimizing their optoelectronic properties.
