InAs Quantum Wells Research Articles

Effect of illumination on the interplay between Dresselhaus and Rashba spin-orbit couplings in InAs quantum wells

We studied the dependence on carrier density of the spin–orbit coupling (SOC) and of the semiconducting properties of a thin n-type InAs quantum well in the limit of high carrier density, when the second subband starts to populate. Measurements of sheet and Hall resistances were performed in a variable magnetic field, temperature, and under illumination with wavelengths of 400 nm up to 1300 nm. Beats in the Shubnikov de Haas oscillations indicated the presence of strong spin–orbit coupling, and the fast Fourier transforms of the oscillations point toward the presence of both Rashba and Dresselhaus spin–orbit interactions. We used simulations to extract the carrier density dependence of the SOCs, based on the Hamiltonian of a single subband 2D electron system with both types of spin–orbit interactions and subject to a perpendicular magnetic field. The results indicate that the Rashba coefficient decreases with increasing the carrier concentration, with an accelerated decrease close to the transition to double occupancy. The Dresselhaus coefficient is not only smaller but also drops in the proximity of the transition, together with the carrier mobility and the Landau level broadening energy. This behavior is discussed in the context of phenomena associated with the onset of double occupancy and based on intersubband interactions.

Full electrostatic control of quantum interference in an extended trenched Josephson junction

Hybrid semiconductor/superconductor devices constitute an important platform for a wide range of applications, from quantum computing to topological-state-based architectures. Here, we demonstrate full modulation of the interference pattern in a superconducting interference device with two parallel islands of ballistic InAs quantum wells separated by a trench, by acting independently on two side-gates. This so far unexplored geometry enables us to tune the device with high precision from a SQUID-like to a Fraunhofer-like behavior simply by electrostatic gating, without the need for an additional in-plane magnetic field. These measurements are successfully analyzed within a theoretical model of an extended tunnel Josephson junction, taking into account the focusing factor of the setup. The impact of these results on the design of novel devices is discussed.

Counterflowing edge current and its equilibration in quantum Hall devices with sharp edge potential: Roles of incompressible strips and contact configuration

We report the observation of counterflowing edge current in InAs quantum wells which leads to the breakdown of quantum Hall (QH) effects at high magnetic fields. Counterflowing edge channels arise from the Fermi-level pinning of InAs and the resultant sharp edge potential with downward bending. By measuring the counterflow conductance for varying edge lengths, we determine the effective number $\langle N_\text{C} \rangle$ of counterflowing modes and their equilibration length $\lambda_\text{eq}$ at bulk integer filling factor $\nu = 1$--$4$. $\lambda_\text{eq}$ increased exponentially with magnetic field $B$, reaching $200~\mu$m for $\nu = 4$ at $B \geq 7.6$~T. Our data reveal important roles of the innermost incompressible strip with even filling in determining $\langle N_\text{C} \rangle$ and $\lambda_\text{eq}$ and the impact of the contact configuration on the QH effect breakdown. Our results show that counterflowing edge channels manifest as transport anomalies only at high fields and in short edges. This in turn suggests that, even in the integer QH regime, the actual microscopic structure of edge states can differ from that anticipated from macroscopic transport measurements, which is relevant to various systems including atomic-layer materials.

Mid-infrared type-I InAs/In0.83Al0.17As quantum wells grown on GaP and InP by gas source molecular beam epitaxy

Type-I InAs quantum wells have been grown on metamorphic In0.83Al0.17As buffers on (0 0 1)-oriented GaP and InP substrates by gas source molecular beam epitaxy. The structural and optical properties as well as strain conditions were characterized and investigated to compare the material quality of samples grown on GaP and InP substrates, respectively. Photoluminescence up to 2.8 μm has been observed for the quantum wells at room temperature. The quantum wells on GaP and InP show the similar photoluminescence intensity, X-ray diffraction peaks and Raman shift performances. These results indicate the potential to demonstrate type-I mid-infrared light sources on Si substrate using GaP as a template.

Design and growth of multi-functional InAsP metamorphic buffers for mid-infrared quantum well lasers on InP

We present InAsP multi-functional metamorphic buffers (MFMBs) designed to enable mid-infrared Type-I InAs quantum well (QW) lasers on InP substrates. InAsxP1-x/InP MFMBs with x = 0.5–0.7 provide a versatile platform for Type-I InAs QW laser diodes in the mid-infrared regime by bridging the lattice mismatch between InAs and InP while simultaneously functioning as the bottom cladding layer for laser structures. Cross-sectional transmission electron microscopy shows that InAs multi-QWs can be grown as thick as 15 nm without forming misfit dislocations on an InAs0.7P0.3 buffer, enabling room-temperature photoluminescence at wavelengths >3 μm. We then compare the performance of lasers grown on InAsP MFMBs and show that the temperature dependence strongly depends on the energy band offset between the QW and the metamorphic InAsP waveguides. Future work could improve performance at longer wavelengths by investigating the use of electron blocking layers and adjusting the device design to minimize parasitic heating.

Contribution of top barrier materials to high mobility in near-surface InAs quantum wells grown on GaSb(001)

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.

Edgeless and purely gate-defined nanostructures in InAs quantum wells

Nanostructures in InAs quantum wells have so far remained outside of the scope of traditional microfabrication techniques based on etching. This is due to parasitic parallel conduction arising from charge carrier accumulation at the physical edges of samples. Here, we present a technique which enables the realization of quantum point contacts and quantum dots in two-dimensional electron gases of InAs purely by electrostatic gating. Multiple layers of top gates separated by dielectric layers are employed. Full quantum point contact pinch-off and measurements of Coulomb-blockade diamonds of quantum dots are demonstrated.

Mid-infrared emissions from In(Ga)As quantum wells grown on GaP/Si(001) substrates

This work reports on the approach of metamorphic In(Ga)As quantum wells on GaP/Si(001) substrates for Si-based mid-infrared applications. Metamorphic InP and In0.83Al0.17As templates are grown on Si, and room temperature photoluminescence emissions at 2.1 μm and 2.6 μm have been demonstrated from InAs/In0.53Ga0.47As triangular quantum wells and InAs quantum wells on the templates, respectively. The surface root mean square roughness is 4-5 nm. The quantum wells act fully strained and the threading dislocation density is 107-108 cm-2 in the upper side of buffer.

High-mobility InAs 2DEGs on GaSb substrates: A platform for mesoscopic quantum transport

High mobility, strong spin-orbit coupling, and large Land\'e g-factor make the two-dimensional electron gas (2DEG) in InAs quantum wells grown on nearly-lattice-matched GaSb substrates an attractive platform for mesoscopic quantum transport experiments. Successful operation of mesoscopic devices relies on three key properties: electrical isolation from the substrate; ability to fully deplete the 2DEG and control residual sidewall conduction with lithographic gates; and high mobility to ensure ballistic transport over mesoscopic length scales. Simultaneous demonstration of these properties has remained elusive for InAs 2DEGs on GaSb substrates. Here we report on heterostructure design, molecular beam epitaxy growth, and device fabrication that result in high carrier mobility and full 2DEG depletion with minimal residual edge conduction. Our results provide a pathway to fully-controlled 2DEG-based InAs mesoscopic devices.

Photoconductivity Amplification in a Type-II n-GaSb/InAs/p-GaSb Heterostructure with a Single QW

Significant photocurrent/photoconductivity amplification is observed at low reverse biases in a type-II n-GaSb/InAs/p-GaSb heterostructure with a single quantum well (QW), grown by metal-organic vapor phase epitaxy. A sharp increase in the photocurrent by more than two orders of magnitude occurs under exposure of the heterostructure to monochromatic light with a wavelength of 1.2–1.6 μm (at 77 K) and the application of a reverse bias in the range 5–200 mV. The optical gain depends on the applied voltage and increases to 2.5 × 102 at a reverse bias of 800 mV. Theoretical analysis demonstrated that the main role in the phenomenon is played by the screening of the external electric field by electrons accumulated in the deep InAs QW and by the mechanism of the tunneling transport of carriers with a small effective mass. It is shown that the effect under study is common to both isotype and anisotype type-II heterojunctions, including structures with QWs and superlattices.

Radiative versus non-radiative recombination in high-efficiency mid-IR InSb/InAs/In(Ga,Al)As/GaAs metamorphic nanoheterostructures

Nanostructures with a submonolayer InSb type-II insertion inside a InAs/InGaAs type-I quantum well (QW) have been grown by molecular beam epitaxy on GaAs (0 0 1) substrates via a convex-graded InAlAs metamorphic buffer layer (MBL). Selection of optimal growth conditions and design of the MBL-virtual substrate system enables one to increase mid-infrared photoluminescence (PL) and internal quantum efficiency (IQE) of the nanoheterostructures. The maximum low temperature IQE of about 90% has been obtained owing to the residual strain engineering which has resulted in both reduction of the extended defect density in the QW, likely responsible for Shockley–Read–Hall non-radiative recombination, and suppression of the Auger recombination channels in the InAs QW and the barriers. Temperature dependence of the integrated PL intensity was analyzed to determine an activation energy of an additional high-temperature non-radiative process (~49 meV) related presumably to hole delocalization through acceptor states in the strained InAs QW.

Эффект увеличения фотопроводимости в гетероструктуре II типа n-GaSb/InAs/p-GaSb с одиночной квантовой ямой

AbstractSignificant photocurrent/photoconductivity amplification is observed at low reverse biases in a type-II n -GaSb/InAs/ p -GaSb heterostructure with a single quantum well (QW), grown by metal-organic vapor phase epitaxy. A sharp increase in the photocurrent by more than two orders of magnitude occurs under exposure of the heterostructure to monochromatic light with a wavelength of 1.2–1.6 μm (at 77 K) and the application of a reverse bias in the range 5–200 mV. The optical gain depends on the applied voltage and increases to 2.5 × 10^2 at a reverse bias of 800 mV. Theoretical analysis demonstrated that the main role in the phenomenon is played by the screening of the external electric field by electrons accumulated in the deep InAs QW and by the mechanism of the tunneling transport of carriers with a small effective mass. It is shown that the effect under study is common to both isotype and anisotype type-II heterojunctions, including structures with QWs and superlattices.

Proximity-induced superconductivity within the InAs/GaSb edge conducting state

We experimentally investigate Andreev transport through the interface between an indium superconductor and the edge of the InAs/GaSb bilayer. To cover all possible regimes of InAs/GaSb spectrum, we study samples with 10 nm, 12 nm, and 14 nm thick InAs quantum wells. For the trivial case of a direct band insulator in 10~nm samples, differential resistance demonstrates standard Andreev reflection. For InAs/GaSb structures with band inversion (12~nm and 14 nm samples), we observe distinct low-energy structures, which we regard as direct evidence for the proximity-induced superconductivity within the current-carrying edge state. For 14~nm InAs well samples, we additionally observe mesoscopic-like resistance fluctuations, which are subjected to threshold suppression in low magnetic fields.

Observation of fractional quantum Hall effect in an InAs quantum well

The two-dimensional electron system in an InAs quantum well has emerged as a prime candidate for hosting exotic quasiparticles with non-Abelian statistics such as Majorana fermions and parafermions. To attain its full promise, however, the electron system has to be clean enough to exhibit electron-electron interaction phenomena. Here, we report the observation of the fractional quantum Hall effect in a very low disorder InAs quantum well with a well width of 24 nm, containing a two-dimensional electron system with a density $n=7.8\ifmmode\times\else\texttimes\fi{}{10}^{11}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ and low-temperature mobility $1.8\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{2}$/Vs. At a temperature of $\ensuremath{\simeq}\phantom{\rule{0.16em}{0ex}}35$ mK and $B\ensuremath{\simeq}24$ T, we observe a deep minimum in the longitudinal resistance, accompanied by a nearly quantized Hall plateau at a Landau level filling factor $\ensuremath{\nu}=4/3$.

Mobility in excess of 106 cm2/V s in InAs quantum wells grown on lattice mismatched InP substrates

We investigate the transport properties of a two-dimensional electron gas residing in strained composite quantum wells of In0.75Ga0.25As/InAs/In0.75Ga0.25As cladded with In0.75Al0.25As barriers grown metamorphically on insulating InP substrates. By optimizing the widths of the In0.75Ga0.25As layers, the In0.75Al0.25As barrier, and the InAs quantum well, we demonstrate mobility in excess of 1×106 cm2/V s. Mobility vs. density data indicate that scattering is dominated by a residual three dimensional distribution of charged impurities. We extract the effective Rashba parameter and spin-orbit length for these composite quantum wells.

Vertical transport in type-II heterojunctions with InAs/GaSb/AlSb composite quantum wells in a high magnetic field

Vertical transport in type-II heterojunctions with a two-barrier AlSb/InAs/GaSb/AlSb quantum well (QW) grown by MOVPE on an n-InAs (100) substrate is investigated in quantizing magnetic fields up to B = 14 T at low temperatures T = 1.5 and 4.2 K. The width of the QWs is selected from the formation condition of the inverted band structure. Shubnikov–de Haas oscillations are measured at two orientations of the magnetic field (perpendicular and parallel) relative to the structure plane. It is established that conduction in the structure under study is occurs via both three-dimensional (3D) substrate electrons and two-dimensional 2D QW electrons under quantum limit conditions for bulk electrons (B > 5 T). The electron concentrations in the substrate and InAs QW are determined. The g-factor for 3D carriers is determined by spin splitting of the zero Landau level. It is shown that the conductance maxima in a magnetic field perpendicular to the structure plane and parallel to the current across the structure in fields B > 9 T correspond to the resonant tunneling of 3D electrons from the emitter substrate into the InAs QW through the 2D electron states of the Landau levels.

Conductance fluctuations in InAs quantum wells possibly driven by Zitterbewegung

The highly successful Dirac equation predicts peculiar phenomena such as Klein tunnelling and Zitterbewegung (ZB) of electrons. From its conception by Erwin Schrödinger, ZB has been considered key in understanding relativistic quantum mechanics. However, observing the ZB of electrons has proved difficult, and instead various emulations of the phenomenon have been proposed producing several successes. Concerning charge transport in semiconductors and graphene, expectations were high but little has been reported. Here, we report a surprisingly large ZB effect on charge transport in a semiconductor nanostructure playing “flat pinball”. The setup is a narrow strip of InAs two-dimensional electron gas with strong Rashba spin–orbit coupling. Six quantum point contacts act as pinball pockets. In transiting between two contacts, ZB appears as a large reproducible conductance fluctuation that depends on the in-plane magnetic field. Numerical simulations successfully reproduced our experimental observations confirming that ZB causes this conductance fluctuation.

Edge transport in InAs and InAs/GaSb quantum wells

We investigate low-temperature transport through single InAs quantum wells and broken-gap InAs/GaSb double quantum wells. Nonlocal measurements in the regime beyond bulk pinch-off confirm the presence of edge conduction in InAs quantum wells. The edge resistivity of $1--2\mathrm{k}\mathrm{\ensuremath{\Omega}}/\ensuremath{\mu}\mathrm{m}$ is of the same order of magnitude as edge resistivities measured in the InAs/GaSb double quantum well system. Measurements in a tilted magnetic field suggests an anisotropy of the conducting regions at the edges with a larger extent in the plane of the sample than normal to it. Finger-gate samples on both material systems shine light on the length dependence of the edge resistance with the intent to unravel the nature of edge conduction in InAs/GaSb coupled quantum wells.

Spin-orbit interaction in InAs/GaSb heterostructures quantified by weak antilocalization

We study the spin-orbit interaction (SOI) in InAs/ GaSb and InAs quantum wells. We show through temperature- and gate-dependent magnetotransport measurements of weak antilocalization that the dominant spin-orbit relaxation mechanism in our low-mobility heterostructures is Elliott-Yafet and not Dyakonov-Perel in the form of the Rashba or Dresselhaus SOI as previously suggested. We compare our findings with recent work on this material system and show that the SOI length lies within the same range. The SOI length may be controlled using an electrostatic gate, opening up prospects for developing spintronic applications.

InSb/InAs/InGa(Al)As/GaAs(0 0 1) metamorphic nanoheterostructures grown by MBE and emitting beyond 3 μm

We report on molecular beam epitaxial growth and properties of InAs/In0.66Ga0.34As/In0.77Al0.23As metamorphic quantum wells (QWs) with submonolayer InSb insertions grown on GaAs(001) substrates. InAlAs metamorphic buffer layers with linear and convex profiles are used to match gradually the lattice parameter from GaAs one to that of In0.77Al0.23As barriers, with the latter profile showing the better structural quality. A single type-II InSb insertion in the InAs QW shifts the photoluminescence (PL) peak maximum well beyond 3μm due to the recombination of holes localized in the InSb well with electrons confined in the InAs/InGaAs QW. The mid-infrared PL in the structures with and without InSb insertion survives up to room temperature.