Selective examination of optically and structurally separable parts within GaAs/AlGaAs core-shell nanowires by micro-photoluminescence and transmission electron microscopy

Abstract

GaAs/AlGaAs core-shell nanowires exhibit properties suitable for electronic and opto-electronic applications. In this work, individual parts of Au and self catalyzed nanowires are examined through microphotoluminescence and transmission electron microscopy. The focus of the work was to find the spatial origin of the various emission energies reported for GaAs nanowires. Parts of wires were selected by sputtering with a focused ion beam, selective deposition of Pt by a focused electron beam and probing sections with the laser beam in photoluminescence experiments. The Au catalyzed wires examined are predominantly of wurtzite crystal phase and of two structurally separable types, short and uniform or long with segments with a high density of stacking faults. The self catalyzed wires have a lower part with zinc blende crystal phase and an upper part with a high density of stacking faults, twinning and small segments of wurtzite phase. The emission from the wires have different spatial and structural origin relating to the varying morphology of the wires. It is found that the emission from the Au catalyzed wires comes from bound excitons and axial AlGaAs. The emission from self catalyzed wires comes from bound excitons or spatially indirect type II transitions relating to stacking faults and twins. It was also found that cutting the wires suppressed their radiative efficiency and that covering the wires with Pt induced surface plasmon resonance at the Pt/NW interface.