Search query: Transport properties of near surface InAs two-dimensional heterostructures

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abstract: Two dimensional electron systems confined to the surface of narrowband semiconductors have attracted great interest since they can easily integrate with superconductivity (or ferromagnetism) enabling new possibilities in hybrid device architectures and study of exotic states in proximity to superconductors. In this work, we study indium arsenide heterostructures where a combination of a clean interface with superconductivity, high mobility, and spin orbit coupling can be achieved. The weak antilocalization measurements indicate the presence of strong spin orbit coupling at high densities. We study the magnetotransport as a function of top barrier and density and report a clear observation of integer quantum Hall states. We report improved electron mobility reaching up to 44 000 cm2/Vs in undoped heterostructures and well developed integer quantum Hall states starting as low as 2.5 T.Two dimensional electron systems confined to the surface of narrowband semiconductors have attracted great interest since they can easily integrate with superconductivity (or ferromagnetism) enabling new possibilities in hybrid device architectures and study of exotic states in proximity to superconductors. In this work, we study indium arsenide heterostructures where a combination of a clean interface with superconductivity, high mobility, and spin orbit coupling can be achieved. The weak antilocalization measurements indicate the presence of strong spin orbit coupling at high densities. We study the magnetotransport as a function of top barrier and density and report a clear observation of integer quantum Hall states. We report improved electron mobility reaching up to 44 000 cm2/Vs in undoped heterostructures and well developed integer quantum Hall states starting as low as 2.5 T.
author_names: Kaushini S Wickramasinghe

William Mayer

Joseph Yuan

Tri Tuan Nguyen

Lu Jiao

Vladimir E Manucharyan

Javad Shabani
title: Transport properties of near surface InAs two dimensional heterostructures
year: 2018

author_names: Joseph Yuan

William Mayer

Kaushini S Wickramasinghe

Javad Shabani
title: Transport Properties Of Near Surface Quantum Wells In InAs Heterostructures
year: 2018

abstract: Near surface InAs two dimensional electron gas (2DEG) systems have great potential for realizing networks of multiple Majorana zero modes towards a scalable topological quantum computer. Improving mobility in the near surface 2DEGs is beneficial for stable topological superconducting states as well as for correlation of multiple Majorana zero modes in a complex network. Here, we investigate near surface InAs 2DEGs (13 nm away from the surface) grown on GaSb(001) substrates, whose lattice constant is closely matched to InAs, by molecular beam epitaxy. The effect of 10 nm thick top barrier to the mobility is studied by comparing Al$_{0.9}$Ga$_{0.1}$Sb and In$_{0.75}$Ga$_{0.25}$As as a top barrier on otherwise identical InAs quantum wells grown with identical bottom barrier and buffer layers. A 3 nm thick capping layer on Al$_{0.9}$Ga$_{0.1}$Sb top barrier also affects the 2DEG electronic transport properties by modifying scattering from 2D remote ionized impurities at the surface. The highest transport mobility of 650,000 cm$^2$/Vs with an electron density of 3.81 \times$ 10${11} cm$ 2} was observed in an InAs 2DEG with an Al$_{0.9}$Ga$_{0.1}$Sb top barrier and an In$_{0.75}$Ga$_{0.25}$As capping layer. Analysis of Shubnikov de Haas oscillations in the high mobility sample suggests that long range scattering, such as remote ionized impurity scattering, is the dominant scattering mechanism in the InAs 2DEGs grown on GaSb(001) substrates. In comparison to InAs quantum wells grown on lattice mismatched InP, the ones grown on GaSb show smoother surface morphology and higher quantum mobility. However, In$_{0.75}$Ga$_{0.25}$As top barrier in InAs quantum well grown on GaSb limits the transport mobility by charged dislocations formed in it, in addition to the major contribution to scattering from the alloy scattering.
author_names: Joon Sue Lee

Borzoyeh Shojaei

Mihir Pendharkar

Mayer Feldman

Kunal Mukherjee

Chris J Palmstrom
title: Contribution of top barrier materials to high mobility in near surface InAs quantum wells grown on GaSb(001)
year: 2018

abstract: We have investigated the anisotropic transport behavior of InAs/AlSb heterostructures grown on a (001) InP substrate. An electrical analysis showed anisotropic sheet resistance Rsh and electron mobility mn in the two dimensional electron gas (2DEG) Hall measurements demonstrated an enhanced anisotropy in mn when cooled from room temperature to 2 K. High electron mobility transistors exhibited 27% higher maximum drain current IDS and 23% higher peak transconductance gm when oriented along the [1 10] direction. The anisotropic transport behavior in the 2DEG was correlated with an asymmetric dislocation pattern observed in the surface morphology and by cross sectional microscopy analysis of the InAs/AlSb heterostructure.
author_names: Giuseppe Moschetti

Huan Zhao

Per Ake Nilsson

Shumin Wang

Alexey Kalabukhov

Gilles Dambrine

S Bollaert

Ludovic Desplanque

Xavier Wallart

Jan V Grahn
title: Anisotropic transport properties in InAs/AlSb heterostructures
year: 2010

abstract: Abstract We have studied the magnetoresistance of a near surface two dimensional electron gas (2DEG) in the presence of a random magnetic field produced by CoPd multilayers deposited onto the surface of the heterostructure. This novel method allows us to switch the random field on and off by applying an external magnetic field and also to control the amplitude and correlation length of the random field by varying the growth parameters of the multilayers. The presence of the random field is confirmed by quenching of the Shubnikov de Haas oscillations and we see an enhanced magnetoresistance which can be interpreted semi classically. We also observe other unusual features which may be quantum in origin.
author_names: Andrew W Rushforth

B L Gallagher

P C Main

A C Neumann

Christopher H Marrows

I Zoller

Mark A Howson

B J Hickey

Mohamed Henini
title: Transport properties of a two dimensional electron gas due to a spatially random magnetic field
year: 2000

abstract: We have studied the magnetoresistance of a near surface two dimensional electron gas (2DEG) in the presence of a random magnetic eld produced by CoPd multilayers deposited onto the surface of the heterostructure. This novel method allows us to switch the random eld on and o by applying an external magnetic eld and also to control the amplitude and correlation length of the random eld by varying the growth parameters of the multilayers. The presence of the random eld is con rmed by quenching of the Shubnikov de Haas oscillations and we see an enhanced magnetoresistance which can be interpreted semi classically. We also observe other unusual features which may be quantum in origin. 2000 Elsevier Science B.V. All rights reserved. PACS: 72.20.My; 73.50.Jt; 75.70 i
author_names: A W Rushfortha

B L Gallaghera

P C Maina

A C Neumanna

C H Marrowsb

I Zollerb

M A Howsonb

B J Hickeyb

M Heninia
title: Transport properties of a two dimensional electron gas due to a spatially randommagnetic eld
year: 2000

abstract: The isolation of a growing number of two dimensional (2D) materials has inspired worldwide efforts to integrate distinct 2D materials into van der Waals (vdW) heterostructures. While a tremendous amount of research activity has occurred in assembling disparate 2D materials into "all 2D" van der Waals heterostructures, this concept is not limited to 2D materials alone. Given that any passivated, dangling bond free surface will interact with another via vdW forces, the vdW heterostructure concept can be extended to include the integration of 2D materials with non 2D materials that adhere primarily through noncovalent interactions. In the first part of this talk I will present our work on emerging mixed dimensional (2D nD, where n is 0, 1 or 3) heterostructure devices performed at Northwestern University. I will present two distinct examples of gate tunable p n heterojunctions 1. Single layer n type MoS2 (2D) combined with p type semiconducting single walled carbon nanotubes (1D) and 2. Single layer MoS2 combined with 0D molecular semiconductor, pentacene. I will present the unique electrical properties, underlying charge transport mechanisms and photocurrent responses in both the above systems using a variety of scanning probe microscopy techniques as well as computational analysis. This work shows that van der Waals interactions are robust across different dimensionalities of materials and can allow fabrication of semiconductor devices with unique geometries and properties unforeseen in bulk semiconductors. Finally, I will briefly discuss our recent work from Caltech on near unity absorption in atomically thin photovoltaic devices.
author_names: Deep Jariwala
title: Mixed Dimensional Van der Waals Heterostructures for Opto Electronics.
year: 2017

abstract: Molecular self assembly is a well known technique to create highly functional nanostructures on surfaces. Self assembly on two dimensional (2D) materials is a developing field driven by the interest in functionalization of 2D materials in order to tune their electronic properties. This has resulted in the discovery of several rich and interesting phenomena. Here, we review this progress with an emphasis on the electronic properties of the adsorbates and the substrate in well defined systems, as unveiled by scanning tunneling microscopy. The review covers three aspects of the self assembly. The first one focuses on non covalent self assembly dealing with site selectivity due to inherent moire pattern present on 2D materials grown on substrates. We also see that modification of intermolecular interactions and molecule substrate interactions influences the assembly drastically and that 2D materials can also be used as a platform to carry out covalent and metal coordinated assembly. The second part deals with the electronic properties of molecules adsorbed on 2D materials. By virtue of being inert and possessing low density of states near the Fermi level, 2D materials decouple molecules electronically from the underlying metal substrate and allow high resolution spectroscopy and imaging of molecular orbitals. The moire pattern on the 2D materials causes site selective gating and charging of molecules in some cases. The last section covers the effects of self assembled, acceptor and donor type, organic molecules on the electronic properties of graphene as revealed by spectroscopy and electrical transport measurements. Non covalent functionalization of 2D materials has already been applied for their application as catalysts and sensors. With the current surge of activity on building van der Waals heterostructures from atomically thin crystals, molecular self assembly has the potential to add an extra level of flexibility and functionality for applications ranging from flexible electronics and OLEDs to novel electronic devices and spintronics.
author_names: Avijit Kumar

Kaustuv Banerjee

Peter Liljeroth
title: Molecular assembly on two dimensional materials.
venue: Nanotechnology
year: 2017

abstract: A bilayer structure of indium arsenide (InAs) and gallium antimonide (GaSb) has been proposed as a two dimensional (2D) electronic system tunable to different states of matter namely the trivial and the topological insulator (TI) phases. 2D TI which is also called quantum spin Hall (QSH) insulator is characterized by an insulating bulk and non dissipative counterpropagating edge states with opposite spin polarizations. These features identify the quantum spin Hall effect where the helical edge states are topologically immune against backscattering guaranteed by time reversal symmetry. Lowtemperature electronic transport measurements may serve to examine the transport properties of InAs/GaSb quantum wells and therefore to inquire into the essence of its bulk and edge behavior. This work is aimed to study the constituents necessary to obtain a robust quantum spin Hall insulator based on InAs/GaSb bilayer heterostructure. We focus on the localization phenomena in InAs/GaSb bilayer quantum wells which are intentionally disordered by silicon atoms. We observed that Si doping near the InAs/GaSb interface significantly alters the transport behavior of these heterostructures. First, we investigated the localization of trivial edge states driven by silicon impurities. As confirmed by recent experimental studies, conductance quantization due to nontrivial edge states, which is the most significant highlight of the QSH effect is obscured by spurious conductivity arising from trivial edge states. In this thesis, we present an experimental observation of the strong localization of trivial edge modes in an InAs/GaSb heterostructure which is weakly disordered by silicon delta like dopants within the InAs layer. The edge conduction which is characterized by a temperature independent behavior at low temperatures and a power law at high temperatures is observed to be exponentially scaled with the length of the edge. Results of comprehensive analyses on measurements done with a range of devices are in agreement with the localization theories in quasi onedimensional electronic systems. Spin orbit interaction is one of the main ingredients of the TIs and in particular in disordered and thus low mobility electronic systems it leads to a weak anti localization characteristic in low field magnetoconductance measurements. As the charge carriers are depleted using a top gate electrode, we observed a crossover from weak anti localization (WAL) to weak localization (WL) This occurs when the dephasing length decreases below the spin orbit characteristic length as a result of enhanced electron electron interactions at lower carrier concentrations. The same crossover is observed with increasing temperature. The linear temperature behavior of inelastic scattering rate indicates that the dominant phase breaking mechanism in our 2D system is due to electron electron interactions. Finally, we compare three heterostructures (Wafers A, B, and C) all delta doped with silicon atoms at different spatial positions in the growth direction near the InAs/GaSb interface. We found the transport behavior of these heterostructures to be very different from each other which can be attributed to the vertical position of disorder within the layered structures. Since the silicon atoms are donors to InAs and acceptors to GaSb, it matters where they are located with respect to the InAs/GaSb interface considering the interfacial effects and potential fluctuations induced by impurities
author_names: Vahid Sazgari Ardakani
title: Localization phenomena in INAS/GASB composite quantum wells with disorder
year: 2019

abstract: Abstract We discuss structural and electrical properties of AlAs x Sb 1 x bulk layers and InAs/AlAs x Sb 1 x heterostructures grown by molecular beam epitaxy over a wide range of composition (0 x 0.4) We demonstrate the strong sensitivity of the structural quality and the composition of Al(As,Sb) on growth parameters such as substrate temperature, As Sb flux ratio, as well as total group V flux, and discuss the influence of a miscibility gap on the molecular beam epitaxial growth of Al(As,Sb) We also find that both the composition and the growth temperature strongly influence the surface morphology: Al(As,Sb) especially when grown at low substrate temperature appears to grow in an island coalescence mode rather than in a two dimensional manner as it does for pure AlAs or AlSb. The electrical transport along AlSb/InAs/Al(As,Sb) quantum wells is strongly influenced by the growth temperature of Al(As,Sb) and we observe the formation of additional defects when the top barrier was grown at low substrate temperature. The transport across InAs/Al(As,Sb) heterojunctions was found to depend on both the growth temperature and the arsenic composition. An increase in arsenic composition results in a strongly decreased current across the heterojunction. From ballistic electron emission spectroscopy experiments, we confirm the transition from a staggered band lineup for InAs/AlSb to a straddled band lineup for InAs/AlAs x Sb 1 x for x =0.16.
author_names: H Blank

S K Mathis

Eric M Hall

S Bhargava

Alexander Behres

Michael Heuken

Herbert Kroemer

Venkatesh Narayanamurti
title: Al(As,Sb) heterobarriers on InAs: growth, structural properties and electrical transport
year: 1998