Atomically Precise GaAs/AlGaAs Quantum Dots Fabricated by Twofold Cleaved Edge Overgrowth

The formation of a $7\times 7\times 7{\mathrm{nm}}^3$ size GaAs quantum dot (QD) at the intersection of three quantum wells is demonstrated for the first time. Intense radiative recombination between zero-dimensional states in the QDs is clearly identified by microscopic photoluminescence ( $\mu \mathrm{PL}$). In contrast to the inhomogeneously broadened quantum well and quantum wire signals originating from the complex twofold cleaved edge overgrowth structure, the strongly spatially localized QD response is characterized by spectrally sharp lines in $\mu \mathrm{PL}$ excitation spectra with a linewidth below $70\mu \mathrm{eV}$.