Single　nanostructures　embedded　within　nanowires　(NWs)　represent　one　of　the　most　promising　technologies　for　applications　in　quantum　photonics.　However,　fabrication　imperfections　and　etching-induced　defects　are　inevitable　for　top-down　fabrications,　whereas　self-assembly　bottom-up　approaches　cannot　avoid　the　difficulties　of　its　stochastic　nature　and　are　limited　to　restricted　heterogeneous　material　systems.　Here　we　demonstrate　the　versatile　self-assembly　of　single　＂square＂　quantum　rings　(QR)　on　the　sidewalls　of　gold-free　GaAs　NWs　for　the　first　time.　By　tuning　the　deposition　temperature,　As　overpressure　and　amount　of　gallium-droplets,　we　were　able　to　control　the　density　and　morphology　of　the　structure,　yielding　novel　single　quantum　dots,　QR,　coupled　QRs,　and　nano-antidots.　A　proposed　model　based　on　a　strain-driven,　transport-dependent　nucleation　of　gallium　droplets　at　high　temperature　accounts　for　the　formation　mechanism　of　these　structures.　We　achieved　a　single-QR-in-NW　structure,　of　which　the　optical　properties　were　analyzed　using　micro-photoluminescence　at　10　K　and　a　spatially　resolved　cathodoluminescence　technique　at　77　K.　The　spectra　show　sharp　discrete　peaks;　of　these　peaks,　the　narrowest　linewidth　(separation)　was　578　mu　eV　(1-3　meV),　reflecting　the　quantized　nature　of　the　ring-type　electronic　states.