Polarization-resolved photoluminescence study of an atom probe tip containing a ZnO-(Mg,Zn)O heterostructure

We studied polarization-resolved photoluminescence originating from a ZnO-(Mg,Zn)O quantum well heterostucture embedded within an atom probe tip, i.e. a nanoscale needle-shaped sample with apex radius of several tens of nm, prepared by focused ion beam. The study was carried out within a photonic atom probe before the atom probe analysis of the sample. This setup allows for the analysis of the polarization of the photoluminescence emitted by the tip and for its orientation around its axis. While the photoluminescence emitted by bulk ZnO and by the (Mg,Zn)O alloy is strongly polarized along the tip axis, coinciding with the crystal [1-100] axis, the ZnO/(Mg,Zn)O quantum well luminescence appears to be strongly polarized along its in-plane direction, perpendicular to the crystal [1-100] axis. Finite-difference time domain calculations provide a key for the interpretation of these results in terms of selection rules and of effects related to the waveguide effect of the tip.