Semiconductor nanowires can consist of different materials.
However, in most cases semiconductor nanowire are made of only a single material, e.g. InAs. Here, the transport properties can be tuned by means of doping. However, by making use of axial or radial heterostructures the nanowire properties can be tailored in a much more versatile fashion. By inserting two semiconductor barriers with a larger band gap in axial direction quantum dot structures can be realized . By covering the nanowire radially by a higher band gap material the surface can be passivated and the surface scattering of the carrier can be reduced .
In Jülich nanowires comprising a radial heterostructure are grown by means of molecular beam epitaxy and metal organic vapor phase epitaxy. The first type of structure can be viewed as a rolled up 2-dimensional electron gas in an AlGaAs/GaAs heterostructure . Here, the GaAs core is surrounded by an AlGaAs barrier layer. The carriers in the GaAs core are supplied by a dopant layer in the AlGaAs shell.
In a different concept of the isolating GaAs core is covered by a conductive InAs shell . Here, the GaAs core can even be removed completely by means of selective wet chemical etching .
On the GaAs/InAs core/shell nanowires magnetotransport measurements were performed . By combining the low band gap shell material with a large band gap core material a tube-like conductor is formed. If at low temperatures a magnetic field is applied along the wire axis very regular oscillations are observed. These oscillations originate from electron interference effects. Particularly at low temperatures the wave properties of electrons are visible. The superposition of these electrons waves lead to interference phenomena, i.e. an enhancement (constructive interference) or a cancelation (destructive interference). By applying a magnetic field the interference pattern measured by the conductance can be shifted periodically.
Electron interference effects might be used for switching purpose in future nano-scaled devices. An advantage would be the superior energy efficiency compared to conventional devices.
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