Abstract
We report both zinc-blende (ZB) and wurtzite (WZ) crystal phase self-assembled GaAs quantum dots (QDs) embedded in single GaAs/AlGaAs core-shell nanowires. Optical transitions and single-photon characteristics of both kinds of QDs have been investigated by measuring photoluminescence (PL) and time-resolved PL spectra upon application of hydrostatic pressure. We find that the ZB QDs are of direct band-gap transition with short recombination lifetime (\ensuremath{\sim}1 ns) and higher pressure coefficient (75--100 meV/GPa). On the contrary, the WZ QDs undergo a direct-to-pseudodirect band-gap transition as a result of quantum confinement effect, with remarkably longer exciton lifetime (4.5--74.5 ns) and smaller pressure coefficient (28--53 meV/GPa). These fundamentally physical properties are further examined by performing state-of-the-art atomistic pseudopotential calculations.
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