Features of electron gas in InAs nanowires imposed by interplay between nanowire geometry, doping and surface states

Abstract

We present a study of electron gas properties in InAs nanowires determined by interaction between nanowire geometry, doping and surface states. The electron gas density and space distribution are calculated via self-consistent solution of coupled Schroedinger and Poisson equations in the nanowires with a hexagonal cross-section. We show that the density of surface states and the nanowire width define the spatial distribution of the electrons. Three configurations can be distinguished, namely the electrons are localized in the center of the wire, or they are arranged in a uniform tubular distribution, or finally in a tubular distribution with additional electron accumulation at the corners of the nanowire. The latter one is dominating for most experimentally obtained nanowires. N-type doping partly suppresses electron accumulation at the nanowire corners. The electron density calculated for both, various nanowire widths and different positions of the Fermi level at the nanowire surface, is compared with the experimental data for intrinsic InAs nanowires. Suitable agreement is obtained by assuming a Fermi level pinning at 60 to 100 meV above the conduction band edge, leading to a tubular electron distribution with accumulation along the corners of the nanowire.Electron and hole gas in semiconductor nanowires of the sizes compared to the de Broglie wavelength is a fascinating object since its properties are determined by quantum-mechanical effects. Moreover, III/V semiconductors offer a wide range of opportunities to change the nanowire material composition, geometry and heterostructure design. This, in turn has a lot of implications, namely nanowires act as a test bed for detailed study of fundamental physics in low-dimensional systems as well as a perspective platform for numerous applications in nanoelectronics, optoelectronics, and spintronics 1-4 . The quantization in the potential landscape of a nanowire is ruled by both the Schroedinger and Poisson equations with appropriate boundary conditions at the surface. Thus, the state of a nanowire surface might strongly govern both charge carrier distribution and density within a nanowire. This apparently holds for InAs surface which is known for its high density of surface states in particular after exposure to air [5][6][7][8][9][10][11][12][13] . It is believed that due to the dominating donor-type surface states, supplying electrons to nanowire body, even intrinsic InAs nanowires have high n-type conductivity without additional doping [14][15][16][17][18][19][20][21][22][23][24] . In addition, low contact resistance of InAs nanowires 25 is another indication for the formation of an electron accumulation layer at the nanowire surface. It is natural to expect that the electron gas formed in InAs nanowires due to the surface states would possess different features depending on the surface states and the nanowire diameter 14,23,[26][27][28][29][30][31][32][33] . So far there exist several studies of electron and hole gas properties in core-shell nanowires, i.e. nano...

Unified numerical approach to topological semiconductor-superconductor heterostructures

“…[22]. InAs is known to have a strong surface accumulation layer at the pristine InAs surface [61,62]. We model [0001] wurtzite InAs nanowires, for which the precise parameters of the surface accumulation layer are presently unknown.…”

“…2. Due to their accumulation layer hexagonal InAs nanowires have a tendency to accumulate a higher density in their corners than below their facets [62]. In the two-facet device there is a corner that is not adjacent to the Al-shell or the backgate.…”

Regaining a Spatial Dimension: Mechanically Transferrable Two-Dimensional InAs Nanofins Grown by Selective Area Epitaxy

“…An additional nice aspect of the nanofins is the potential for accumulation of high electron density at the two nanofin edges because each edge has three facet corners. 12,13 These might provide natural 1D channels for use in parafermion-based device designs.…”

“…Improved contact arrangements facilitate better understanding of materials by enabling us to measure transport mobility versus carrier density rather than resort to single-figure metrics, e.g., field-effect mobility, that are used by necessity in nanowires due to contact limitations. 11 Finally, by depositing patterned superconductor films and exploiting electron density accumulation at the facet corners 12,13 at opposite edges of the nanofin, exciting new pathways to Majorana/parafermion zero-mode devices 14,15 for topological quantum computation applications may be possible. 16 III-V nanowires were originally and are still commonly grown from a nanoparticle catalyst using a vapor-liquid-solid (VLS) approach.…”

Magnetoconductance correction in zinc-blende semiconductor nanowires with spin-orbit coupling

“…The WAL/WL effect in the diffusive regime was analyzed by Kettemann [32] and Wenk [33,34] for planar quantum wires with a zinc-blende lattice. In our preceding article [14], we developed a model for diffusive zinc-blende nanowires where the transport is governed by surface states, which occurs in materials with Fermi level surface pinning [12,25,30,35,36] or core/shell nanowires [26].…”