Observation of type-II recombination in single wurtzite/zinc-blende GaAs heterojunction nanowires

We have investigated a large set of individual wurtzite/zinc-blende GaAs heterojunction nanowires using transmission electron microscopy (TEM), photoluminescence (PL), and cathodoluminescence (CL). In several cases we have combined PL and TEM on the same wire. We find a fairly deep emission that shows a strong blueshift with increasing excitation power density. By using a variety of experiments we show that this emission is due to recombination across a heterojunction with a type II band alignment. The data give a valence band offset of about 100 meV, in excellent agreement with theoretical predictions. Spatially resolved CL data on heterojunction nanowires and PL data on pure wurtzite nanowires show that the band gap of wurtzite GaAs is very close to the band gap of zinc-blende GaAs.