  The Stranski-Krastanov (SK) growth-mode facilitates the self-assembly of
quantum dots (QDs) using lattice-mismatched semiconductors, for instance InAs
and GaAs. SK QDs are defect-free and can be embedded in heterostructures and
nano-engineered devices. InAs QDs are excellent photon emitters: QD-excitons,
electron-hole bound pairs, are exploited as emitters of high quality single
photons for quantum communication. One significant drawback of the SK-mode is
the wetting layer (WL). The WL results in a continuum rather close in energy to
the QD-confined-states. The WL-states lead to unwanted scattering and dephasing
processes of QD-excitons. Here, we report that a slight modification to the
SK-growth-protocol of InAs on GaAs -- we add a monolayer of AlAs following InAs
QD formation -- results in a radical change to the QD-excitons. Extensive
characterisation demonstrates that this additional layer eliminates the
WL-continuum for electrons enabling the creation of highly charged excitons
where up to six electrons occupy the same QD. Single QDs grown with this
protocol exhibit optical linewidths matching those of the very best SK QDs
making them an attractive alternative to standard InGaAs QDs.
