Daniel Jacobsson

A general approach for sharp crystal phase switching in InAs, GaAs, InP, and GaP nanowires using only group V flow.

III-V-based nanowires usually exhibit random mixtures of wurtzite (WZ) and zinc blende (ZB) crystal structure, and pure crystal phase wires represent the exception rather than the rule. In this work, the effective group V hydride flow was the only growth parameter which was changed during MOVPE growth to promote transitions from WZ to ZB and from ZB to WZ. Our technique works in the same way for all investigated III-Vs (GaP, GaAs, InP, and InAs), with low group V flow for WZ and high group V flow for ZB conditions. This strongly suggests a common underlying mechanism. It displays to our best knowledge the simplest changes of the growth condition to control the nanowire crystal structure. The inherent reduction of growth variables is a crucial requirement for the interpretation in the frame of existing understanding of polytypism in III-V nanowires. We show that the change in surface energetics of the vapor-liquid-solid system at the vapor-liquid and liquid-solid interface is likely to control the crystal structure in our nanowires.

Interface dynamics and crystal phase switching in GaAs nanowires

Controlled formation of non-equilibrium crystal structures is one of the most important challenges in crystal growth. Catalytically grown nanowires are ideal systems for studying the fundamental physics of phase selection, and could lead to new electronic applications based on the engineering of crystal phases. Here we image gallium arsenide (GaAs) nanowires during growth as they switch between phases as a result of varying growth conditions. We find clear differences between the growth dynamics of the phases, including differences in interface morphology, step flow and catalyst geometry. We explain these differences, and the phase selection, using a model that relates the catalyst volume, the contact angle at the trijunction (the point at which solid, liquid and vapour meet) and the nucleation site of each new layer of GaAs. This model allows us to predict the conditions under which each phase should be observed, and use these predictions to design GaAs heterostructures. These results could apply to phase selection in other nanowire systems.

Direct Imaging of Atomic Scale Structure and Electronic Properties of GaAs Wurtzite and Zinc Blende Nanowire Surfaces.

Using scanning tunneling microscopy and spectroscopy we study the atomic scale geometry and electronic structure of GaAs nanowires exhibiting controlled axial stacking of wurtzite (Wz) and zinc blende (Zb) crystal segments. We find that the nonpolar low-index surfaces {110}, {101[overline]0}, and {112[overline]0} are unreconstructed, unpinned, and without states in the band gap region. Direct comparison between Wz and Zb GaAs reveal a type-II band alignment and a Wz GaAs band gap of 1.52 eV.

High crystal quality wurtzite-zinc blende heterostructures in metal-organic vapor phase epitaxy-grown GaAs nanowires

AbstractWe have prepared GaAs wurtzite (WZ)-zinc blende (ZB) nanowire heterostructures by Au particle-assisted metal-organic vapor phase epitaxy (MOVPE) growth. Superior crystal quality of both the transition region between WZ and ZB and of the individual segments themselves was found for WZ-ZB single heterostructures. Pure crystal phases were achieved and the ZB segments were found to be free of any stacking defects, whereas the WZ sections showed a maximum stacking fault density of 20 μm−1. The hexagonal cross-sectional wires are terminated by

Confinement in Thickness-Controlled GaAs Polytype Nanodots.

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GaAs/AlGaAs heterostructure nanowires studied by cathodoluminescence

-type side facets for the WZ segment and predominantly {110}-type side facets for the ZB part of the wire. A diameter increase occurred after the transition from WZ to ZB. Additionally, facets of the

Strategies to obtain pattern fidelity in nanowire growth from large-area surfaces patterned using nanoimprint lithography

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