Quantum Dots in an InSb Two-Dimensional Electron Gas

Abstract

Indium antimonide (InSb) two-dimensional electron gases (2DEGs) have a unique combination of material properties: high electron mobility, strong spin-orbit interaction, large Landé g-factor, and small effective mass. This makes them an attractive platform to explore a variety of mesoscopic phenomena ranging from spintronics to topological superconductivity. However, there exist limited studies of quantum confined systems in these 2DEGs, often attributed to charge instabilities and gate drifts. We overcome this by removing the δ-doping layer from the heterostructure, and induce carriers electrostatically. This allows us to perform the first detailed study of stable gate-defined quantum dots in InSb 2DEGs. We demonstrate two distinct strategies for carrier confinement and study the charge stability of the dots. The small effective mass results in a relatively large single particle spacing, allowing for the observation of an even-odd variation in the addition energy. By tracking the Coulomb oscillations in a parallel magnetic field we determine the ground state spin configuration and show that the large g-factor (∼30) results in a singlet-triplet transition at magnetic fields as low as 0.3 T.Mesoscopic devices can be made in a two-dimensional electron gas (2DEG) using electrical gates to confine charge carriers, thus reducing the degrees of freedom. The extreme case is the zero-dimensional system, a quantum dot (QD). QDs have been used to explore a wide range of quantum phenomena 1-3 , and are emerging as a platform for quantum computing 4-6 and quantum simulations 7-9 . QDs in materials with strong spin-orbit interaction have important applications in the field of topological superconductivity. They can be used to realize Majorana zero modes in quantum dot chains 10 , and are essential elements for the readout and manipulation of topological qubits 11,12 .InSb is a promising material in this regard, with a high carrier mobility, large g-factor and strong spinorbit interaction [13][14][15][16] . QDs have been extensively studied in InSb nanowires [17][18][19] and, more recently, in InSb nanoflakes 20 . However, despite the clear benefits of scalability offered by InSb 2DEGs, experimental reports of confined systems in these quantum wells are scarce 14,21,22 . Thus far, most studies of InSb 2DEGs have been limited to heterostructures where carriers are generated in the quantum well via remote δ-doping layers. Such doped 2DEGs are known to suffer from charge instability and gate drifts, which are particularly detrimental to the study of nanostructures.Here, we show that removal of doping layers enables the realization of highly stable gate-defined quantum dots in InSb 2DEGs. We study two different QD designs on deep and shallow undoped quantum wells. In all measured devices, the charge stability diagrams show welldefined Coulomb diamonds and excited states. We find that the small effective mass of InSb results in a large separation between single-particle levels, enabling the observation of an even-odd periodicity in ...

Field effect two-dimensional electron gases in modulation-doped InSb surface quantum wells

“…Wafer G2 Eight gated Hall bars (see Table I and Figure 1) were fabricated using standard optical lithography and wetetching techniques, keeping all processes at or below a temperature of 150 • C to prevent the deterioration of device characteristics, 14,18,19 and preventing the InSb surface from coming into contact with photoresist developer (see Section I of the Supplementary Material for more details on sample fabrication). Ti/Au Ohmic contacts were deposited directly on the doped n-InSb layer.…”

“…11 a) corresponding author: francois.sfigakis@uwaterloo.ca b) baugh@uwaterloo.ca InSb QWs have generally relied on the use of modulationdoping for 2DEG formation, but these structures have frequently reported issues with parasitic parallel conduction and unstable carrier densities. [12][13][14][15] This is especially true of InSb surface QWs, which must contend with a Schottky barrier at the surface. Dopant-free field-effect 2DEGs avoid these issues and have recently been reported in undoped InSb QWs.…”

The $\mathbf{Z}_{2}$ topological invariants in 2D and 3D topological superconductors without time reversal symmetry

“…Over recent years, topological superconductors (TSCs) have drawn much attention in condensed matters for the novel properties of Majorana zero boundary states [1][2][3][4] and the promising applications in quantum computation [5][6][7][8]. People find a lot of ways to realize and study the TSCs, including quantum dots [9][10][11][12][13][14], dopping topological insulators [15][16][17][18][19][20][21], promxity effect between topological insulators and superconductors [22][23][24][25][26][27], and arranging magnetic atomic on the surface of an swave with hlical structures [28][29][30][31][32][33][34][35][36] or SOC effect [37][38][39][40][41][42][43][44].…”

A double quantum dot defined by top gates in a single crystalline InSb nanosheet*

“…Charge instabilities, gate hysteresis and leakage problems [11][12][13] have limited the realization and investigations of high-quality, confined systems in heterostructured InSb quantum wells capped with thick buffer layers [14][15][16] . Recently, by removing the doping layer from an InSb heterostructure and by inducing carriers to the InSb quantum well electrostatically, a progress in the realization of stable gate-defined QDs in an InSb quantum well has been achieved [17] . An alternative approach is to employ a free-standing InSb nanolayer, i.e., a single crystalline InSb structure without any other material layers and doping layers around.…”