High Mobility One- and Two-Dimensional Electron Systems in Nanowire-Based Quantum Heterostructures

Free-standing semiconductor nanowires in
combination with advanced gate-architectures hold an exceptional
promise as miniaturized building blocks in future
integrated circuits. However, semiconductor nanowires are
often corrupted by an increased number of close-by surface
states, which are detrimental with respect to their optical and
electronic properties. This conceptual challenge hampers their
potentials in high-speed electronics and therefore new
concepts are needed in order to enhance carrier mobilities.
We have introduced a novel type of core−shell nanowire
heterostructures that incorporate modulation or remote doping and hence may lead to high-mobility electrons. We demonstrate
the validity of such concepts using inelastic light scattering to study single modulation-doped GaAs/Al0.16Ga0.84As core-multishell
nanowires grown on silicon. We conclude from a detailed experimental study and theoretical analysis of the observed spin and
charge density fluctuations that one- and two-dimensional electron channels are formed in a GaAs coaxial quantum well spatially
separated from the donor ions. A total carrier density of about 3 × 107 cm−1 and an electron mobility in the order of 50 000 cm2/
(V s) are estimated. Spatial mappings of individual GaAs/Al0.16Ga0.84As core−multishell nanowires show inhomogeneous
properties along the wires probably related to structural defects. The first demonstration of such unambiguous 1D- and 2Delectron
channels and the respective charge carrier properties in these advanced nanowire-based quantum heterostructures is the
basis for various novel nanoelectronic and photonic devices.