Single-electron transport in InAs nanowire quantum dots formed by crystal phase engineering

Abstract

We report electrical characterization of quantum dots formed by introducing pairs of thin wurtzite (WZ) segments in zinc blende (ZB) InAs nanowires. Regular Coulomb oscillations are observed over a wide gate voltage span, indicating that WZ segments create significant barriers for electron transport. We find a direct correlation of transport properties with quantum dot length and corresponding growth time of the enclosed ZB segment. The correlation is made possible by using a method to extract lengths of nanowire crystal phase segments directly from scanning electron microscopy images, and with support from transmission electron microscope images of typical nanowires. From experiments on controlled filling of nearly empty dots with electrons, up to the point where Coulomb oscillations can no longer be resolved, we estimate a lower bound for the ZB-WZ conduction-band offset of 95 meV.

Nonlinear thermoelectric efficiency of superlattice-structured nanowires

“…We also assume δE C = 100 meV, which is close to the value extracted from recent experiments [22] for the barrier height associated with wurtzite segments in a zinc blende InAs NW. Furthermore, we use w = 15 nm, d = 10 nm, and, unless otherwise stated, seven barriers.…”

“…To investigate the demands our proposal sets on epitaxial NW growth, we investigate how the results depend on the number of barriers, showing that a rather small number is sufficient, as well as the sensitivity to random imperfections in the barrier width and separation. We here use parameters valid for InAs NWs, where barriers can be formed by controllable growth of InP segments [18] or of segments of wurtzite structure in an otherwise zinc blende NW [19][20][21][22].…”

Individually addressable double quantum dots formed with nanowire polytypes and identified by epitaxial markers

“…QDs are also elemental in other semiconductor quantum systems that are promising for use in quantum computers and quantum systems in general [4,5,7], such as Majorana fermions [8][9][10][11]. QDs are commonly defined by gate depletion [2,5,12], but progress has been made in material-defined QDs as well [13][14][15]. The material-defined approach allows for more well-defined features and less coupling to external noise.…”

“…The material-defined approach allows for more well-defined features and less coupling to external noise. In this letter, we utilize recently developed InAs polytype bandgap engineering [15][16][17] to define DQDs with a hard-wall potential. With epitaxial markers, we gain control of the individual dots and, demonstrate the honeycomb-shaped charge stability diagrams of material-defined DQDs and the robustness of the system with a wide range of electron populations.The most common approach to forming quantum dots for transport experiments is to start from a material system that is already structurally confined in one or two dimensions and use electrostatic gating to confine the remaining dimensions.Examples here include two-dimensional electron gases [2,5], one-dimensional carbon nanotubes and semiconductor nanowires [12].…”

“…The material-defined approach allows for more well-defined features and less coupling to external noise. In this letter, we utilize recently developed InAs polytype bandgap engineering [15][16][17] to define DQDs with a hard-wall potential. With epitaxial markers, we gain control of the individual dots and, demonstrate the honeycomb-shaped charge stability diagrams of material-defined DQDs and the robustness of the system with a wide range of electron populations.…”