| dc.description.abstract | The structure
of self-catalyzed GaAs NWs (length ~10 µm and thickness ~400 nm) with six GaAsSb/GaAs superlattices
(SL), have been analyzed. Four samples with varying Sb flux and GaAsSb well growth
time, which all depicted lasing when optically pumped, were studied by conventional transmission
electron microscopy. Crystal phase analysis has been done by dark-field imaging, and compared
to high-resolution lattice images. The aim of this work was to quantify the crystal phases
in the different NWs for all the SLs and link the findings to the growth conditions and observed
lasing. The sample with the lowest Sb flux has a very high stacking fault density along the entire
NW, and phase distribution is not further analyzed. The spacers between SLs are wurtzite
(WZ) GaAs, and the SLs consist of defect-free zinc-blende (ZB) phase segments separated by
regions of high stacking fault density and mixed phases (ie. twinned ZB, stacking faults and in
cases WZ). When considering crystal phase, SL-3, -4 and -5 are quite similar, while SL-6 is in
general shorter than other SLs. The ZB segments become larger and more stable, mixed phase
regions reduce in size, over all stacking fault density goes down and the amount of defect-free
WZ phase increases with Sb concentration. In addition, some specific structural features have
been observed; SL-1 has quantum dot-like features, the NW tips have distinct facet planes, and
one sample has surface damage from oxidation of the AlGaAs shell due to incomplete, or absence
of, the GaAs protective cap. The structural characterization carried out in this work helps
to understand the observed lasing behavior and compositional analysis from other studies on
the same NW batches. Together these findings can contribute to optimize the growth of NWs
with GaAs/GaAsSb SLs and the understanding as well as performance of NW-based lasers based
on these heterostructures. | en |
