Micro-photoluminescence study of single GaAsSb/GaAs radial and axial heterostructured core-shell nanowires

We report on the low temperature micro-photoluminescence (μ-PL) of single GaAs/AlGaAs core-shell nanowires (NWs) with axial GaAsSb core-inserts grown by Au-assisted molecular beam epitaxy. The GaAs NW core has hexagonal wurtzite (WZ) crystal structure, whereas the GaAsSb NW core-insert has cubic zinc blende (ZB) crystal structure. The upper GaAsSb/GaAs interface contains a few nm thin cubic ZB GaAs segment just before the crystal structure switches back to WZ. By adding a growth interruption (GI) directly after the GaAsSb insert, the ZB GaAs segment in the WZ GaAs barrier can be avoided. This GI-induced crystal structure change of the upper GaAs barrier next to the GaAsSb/GaAs interface makes a large difference on the PL properties from the GaAsSb NW core-inserts. This is believed to be due to that the GaAsSb/GaAs heterojunction band alignment is changed from type II to type I when the GaAs crystal structure is changed from ZB to WZ.