InSb Quantum Wells Research Articles

Quantum Hall effect in InAsSb quantum wells at elevated temperatures

We have characterized the electronic properties of a high-mobility two-dimensional electron system in modulation doped InAsSb quantum wells and compare them to InSb quantum wells grown in a similar fashion. Using temperature-dependent Shubnikov-de Haas experiments as well as FIR transmission, we find an effective mass of m*≈0.022me, which is lower than in the investigated InSb quantum well, but due to a rather strong confinement still higher than in the corresponding bulk compound. The effective g-factor was determined to be g*≈24.1. These results are also corroborated by k·p band structure calculations. When spin polarizing the electrons in a tilted magnetic field, the g-factor is significantly enhanced by electron-electron interactions, reaching a value as large as g*=60 at a spin polarization P=0.75. Finally, we show that due to the low effective mass, the quantum Hall effect in our particular sample can be observed up to a temperature of 60 K. Published by the American Physical Society 2024

Gate-defined two-dimensional hole and electron systems in an undoped InSb quantum well

Quantum transport measurements are performed in gate-defined, high-quality, two-dimensional hole and electron systems in an undoped InSb quantum well. For both polarities, the carrier systems show tunable spin-orbit interaction as extracted from weak antilocalization measurements. The effective mass of InSb holes strongly increases with carrier density as determined from the temperature dependence of Shubnikov--de Haas oscillations. Coincidence measurements in a tilted magnetic field are performed to estimate the spin susceptibility of the InSb two-dimensional hole system. The $g$ factor of the two-dimensional hole system decreases rapidly with increasing carrier density.

High-quality two-dimensional electron gas in undoped InSb quantum wells

We report on transport experiments through high-mobility gate-tunable undoped InSb quantum wells (QWs). Due to the elimination of any Si modulation doping, the gate-defined two-dimensional electron gases in the QWs display a significantly increased mobility of $260\phantom{\rule{0.16em}{0ex}}000\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}/\mathrm{Vs}$ at a rather low density of $2.4\phantom{\rule{4pt}{0ex}}\ifmmode\times\else\texttimes\fi{}{10}^{11}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\text{--}2}$. Using magnetotransport experiments, we characterize spin-orbit interactions by measuring weak antilocalization. Furthermore, by measuring Shubnikov--de Haas oscillations in tilted magnetic fields, we find that the $g$ factor agrees with $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ theory calculations at low magnetic fields but grows with spin polarization and carrier density at high magnetic fields. Additionally, signatures of Ising quantum Hall ferromagnetism are found at filling factor $\ensuremath{\nu}=2$ for tilt angles where the Landau level energy equals the Zeeman energy. Despite the high mobility, the undoped InSb QWs exhibit no fractional quantum Hall effect up to magnetic fields of 25 T.

Electronic g factor and magnetotransport in InSb quantum wells

High mobility InSb quantum wells with tunable carrier densities are investigated by transport experiments in magnetic fields tilted with respect to the sample normal. We employ the coincidence method and the temperature dependence of the Shubnikov-de Haas oscillations and find a value for the effective g-factor of $\mid g^{\ast}\mid $ =35$\pm$4 and a value for the effective mass of $m^*\approx0.017 m_0$, where $m_0$ is the electron mass in vacuum. Our measurements are performed in a magnetic field and a density range where the enhancement mechanism of the effective g-factor can be neglected. Accordingly, the obtained effective g-factor and the effective mass can be quantitatively explained in a single particle picture. Additionally, we explore the magneto-transport up to magnetic fields of 35 T and do not find features related to the fractional quantum Hall effect.

Landau polaritons in highly nonparabolic two-dimensional gases in the ultrastrong coupling regime

We probe ultra-strong light matter coupling between metallic terahertz metasurfaces and Landau-level transitions in high mobility 2D electron and hole gases. We utilize heavy-hole cyclotron resonances in strained Ge and electron cyclotron resonances in InSb quantum wells, both within highly non-parabolic bands, and compare our results to well known parabolic AlGaAs/GaAs quantum well (QW) systems. Tuning the coupling strength of the system by two methods, lithographically and by optical pumping, we observe a novel behavior clearly deviating from the standard Hopfield model previously verified in cavity quantum electrodynamics: an opening of a lower polaritonic gap.

Toward durable Al-InSb hybrid heterostructures via epitaxy of 2ML interfacial InAs screening layers

The large Land\'{e} g-factor, high spin-orbit coupling, and low effective mass of the two-dimensional electron gas in InSb quantum wells combined with proximal superconductivity may realize a scalable platform for topological quantum computation. Aluminum thin films directly deposited on top of InSb planar structures result in the formation of a reactive AlInSb layer at the interface. This interlayer progressively consumes the whole Al film, resulting in a disordered AlInSb layer after few months at room temperature. We report on a heterostructure design that results in a significant increase of the durability of these hybrid Al-InSb heterostructures with the preservation of a pure Al film and sharp superconductor-semiconductor interface for more than one year. Two monolayers of epitaxial InAs at the superconductor-semiconductor interface prevent interfacial reactivity as evidenced by X-ray reflectivity and energy dispersive spectroscopy measurements. Structural characterizations of the Al films by transmission electron microscopy reveal the presence of tens of nanometers wide grains predominantly oriented with Al(110) parallel to InSb(001).

Improved Electron Transport Properties of Ga1–xInxSb Quantum Well Channel Using Strained‐Al0.40In0.60Sb/Al1–yInySb Stepped Buffer

Unstrained Ga1–xInxSb quantum well (QW) channel using strained‐Al0.40In0.60Sb/Al1–yInySb stepped buffer layer grown on GaAs (100) substrate is investigated. Ga1–xInxSb QW is lattice‐matched to the Al1–yInySb lower buffer layer. Sheet electron density (Ns) of Ga1–xInxSb QW is about twice that of InSb one. Electron mobility (μ) increases with increasing In content x of Ga1–xInxSb. Unstrained Ga0.22In0.78Sb QW channel using strained‐Al0.40In0.60Sb/Al0.25In0.75Sb stepped buffer has Ns of 2.05 × 1012 cm−2 and μ of 15 500 cm2 V−1 s−1. Compared with the InSb QW channel, Ns increases by a factor of 193% and μ decreases to 87%. Consequently, the sheet resistance decreases to 59%. These results indicate that the unstrained Ga1–xInxSb QW channel using strained‐Al0.40In0.60Sb/Al1–yInySb stepped buffer is effective to improve the electron transport properties.

Ballistic superconductivity and tunable \u03c0\u2013junctions in InSb quantum wells

Planar Josephson junctions (JJs) made in semiconductor quantum wells with large spin-orbit coupling are capable of hosting topological superconductivity. Indium antimonide (InSb) two-dimensional electron gases (2DEGs) are particularly suited for this due to their large Landé g-factor and high carrier mobility, however superconducting hybrids in these 2DEGs remain unexplored. Here we create JJs in high quality InSb 2DEGs and provide evidence of ballistic superconductivity over micron-scale lengths. A Zeeman field produces distinct revivals of the supercurrent in the junction, associated with a 0−π transition. We show that these transitions can be controlled by device design, and tuned in-situ using gates. A comparison between experiments and the theory of ballistic π-Josephson junctions gives excellent quantitative agreement. Our results therefore establish InSb quantum wells as a promising new material platform to study the interplay between superconductivity, spin-orbit interaction and magnetism.

Quantum transport in high-quality shallow InSb quantum wells

InSb is one of the promising candidates to realize a topological state through proximity induced superconductivity in a material with strong spin–orbit interactions. In two-dimensional systems, thin barriers are needed to allow strong coupling between superconductors and semiconductors. However, it is still challenging to obtain a high-quality InSb two-dimensional electron gas in quantum wells close to the surface. Here, we report on a molecular beam epitaxy grown heterostructure of InSb quantum wells with substrate-side Si-doping and ultrathin InAlSb (5 nm, 25 nm, and 50 nm) barriers to the surface. We demonstrate that the carrier densities in these quantum wells are gate-tunable and electron mobilities up to 350 000 cm2(V s)−1 are obtained from magnetotransport measurements. Furthermore, from temperature-dependent magnetoresistance measurements, we obtain an effective mass of 0.02 m0 and find Zeeman splitting compatible with the expected band edge g-factor.

Limiting scattering processes in high-mobility InSb quantum wells grown on GaSb buffer systems

We present molecular beam epitaxial grown single- and double-side $\delta$-doped InAlSb/InSb quantum wells with varying distances down to 50 nm to the surface on GaSb metamorphic buffers. We analyze the surface morphology as well as the impact of the crystalline quality on the electron transport. Comparing growth on GaSb and GaAs substrates indicates that the structural integrity of our InSb quantum wells is solely determined by the growth conditions at the GaSb/InAlSb transition and the InAlSb barrier growth. The two-dimensional electron gas samples show high mobilities of up to 349 000 cm$^2$/Vs at cryogenic temperatures and 58 000 cm$^2$/Vs at room temperature. With the calculated Dingle ratio and a transport lifetime model, ionized impurities predominantly remote from the quantum well are identified as the dominant source of scattering events. The analysis of the well pronounced Shubnikov$-$de Haas oscillations reveals a high spin-orbit coupling with an effective $g$-factor of $-38.4$ in our samples. Along with the smooth surfaces and long mean free paths demonstrated, our InSb quantum wells are increasingly competitive for nanoscale implementations of Majorana mode devices.

Resistively Detected Nuclear Magnetic Resonance in Gated Insb QW at Elevated Temperature for Quantum Information Processing

M. M. Uddin,1,2* H. W. Liu,3,4 K. F. Yang,3 T. D. Mishima,5 M. B. Santos,5 K. Nagase,3 and Y. Hirayama1,3,6 1 Department of Physics, Tohoku University, Sendai, Miyagi 980-8578, Japan 2 Department of Physics, Chittagong University of Engineering & Technology, Chittagong-4349, Bangladesh 3 ERATO Nuclear Spin Electronics Project, Sendai, Miyagi 980-8578, Japan 4 State Key Laboratory of Superhard Materials and Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, People’s Republic of China 5 Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks, Norman, Oklahoma 73019-2061, USA 6 WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan *E-mail: mohi_cuet@yahoo.com Narrow band-gap semiconductor InSb has long been considered as potentially exciting materials for next-generation high-speed electronics, quantum devices and spintronics applications due to its high room-temperature mobility (77000 cm2/Vs), significant ballistic transport length, large Lande g factor, high nuclear spin (In=9/2, 121Sb I = 5/2, 123Sb I = 7/2) and high spin-orbit coupling. Nuclear spins in low-dimensional semiconductor structures have attracted growing interest because the long spin coherence time of nuclei facilitates the implementation of quantum information processing (QIP). The quadrupole splitting of 115In have been reported in a single InSb two dimensional electron gas (2DEG) that are of practical importance for the coherent control of the ten nuclear-spin quantum levels and for the implementation of multiple NMR-based quantum bits (≥2) [1, 2]. The success of gate controlled InSb quantum wells [3, 4] allows us to perform pump and probe technique to investigate temperature dependent nuclear spin relaxation time T 1 at different filling factors (ν ). Collective spin excitations in the domain walls enhance dynamic nuclear polarization in the quantum Hall ferromagnet around 2 characterized by a short (~ 60 sec) and temperature-independent T 1. On the other hand, relatively long (~ 400 sec) and temperature dependent T 1with following Korringa law have been demonstrated in the absence of the domains as well as collective spin texture at around 3. In addition, the large Zeeman, cyclotron and exchange energy scales of the InSb 2DEG favour to demonstrate the resistively detected NMR (RDNMR) signal at elevated temperature up to 6 K. Our results clearly show that the InSb 2DEG is a suitable candidate for implementation of the high temperature nuclear-spin based QIP. Ref: [1] H. W. Liu et al. Phys. Rev. B 82, 241304(R) (2010). [2] K. F. Yang et al., Appl. Phys. Lett. 98, 142109 (2011). [3] M. M. Uddin et al., Appl. Phys. Lett. 101, 233503 (2012). [4] M. M. Uddin et al., Appl. Phys. Lett. 103, 123502 (2013). Fig. : Filling factors (ν) dependence of nuclear spin relaxation time T 1 at different temperature. Top axis shows the filling factors are calculated by gate bias (V g) in bottom axis. Figure 1

Gapped superconductivity with all symmetries in InSb (110) quantum wells in proximity tos-wave superconductor in Fulde-Ferrell-Larkin-Ovchinnikov phase or with a supercurrent

We show that all the singlet even-frequency, singlet odd-frequency, triplet even-frequency and triplet odd-frequency pairings, and together with the corresponding order parameters (gaps) can be realized in InSb (110) spin-orbit-coupled quantum well in proximity to s-wave superconductor in Fulde-Ferrell-Larkin-Ovchinnikov phase or with a supercurrent. It is revealed that with the singlet even-frequency order parameter induced by the proximity effect, triplet even-frequency pairing is induced due to the broken spin-rotational symmetry by the spin-orbit coupling. Since the translational symmetry is broken by the center-of-mass momentum of Cooper pair in the Fulde-Ferrell-Larkin-Ovchinnikov phase or with a supercurrent, the singlet odd-frequency pairing can be induced. With the translational and spin-rotational asymmetries, the triplet odd-frequency pairing is also realized. Then, we show that the corresponding order parameters can be obtained from the self-energy of the electron-electron Coulomb interaction with the dynamic screening. The singlet and the induced triplet even-frequency order parameters are found to exhibit the conventional s-wave and p-wave characters in the momentum space, respectively. Whereas for the induced odd-frequency order parameters in quantum well, the singlet and triplet ones show the p-wave and d-wave characters, respectively. Moreover, the p-wave character of the singlet odd-frequency order parameter exhibits anisotropy with respect to the direction of the center-of-mass momentum. While for the triplet one, we find that $d_{x^2}$-wave and $d_{xy}$-wave characters can be obtained with respect to the direction of the center-of-mass momentum. ......

Gapped tripletp-wave superconductivity in strong spin-orbit-coupled semiconductor quantum wells in proximity tos-wave superconductor

We show that the {\it gapped} triplet superconductivity, i.e., a triplet superconductor with triplet order parameter, can be realized in strong spin-orbit-coupled quantum wells in proximity to $s$-wave superconductor. It is revealed that with the singlet order parameter induced from the superconducting proximity effect, in quantum wells, not only can the triplet pairings arise due to the spin-orbit coupling, but also the triplet order parameter can be induced due to the repulsive effective electron-electron interaction, including the electron-electron Coulomb and electron-phonon interactions. This is a natural extension of the work of de Gennes, in which the repulsive-interaction-induced singlet order parameter arises in the normal metal in proximity to $s$-wave superconductor [Rev. Mod. Phys. {\bf 36}, 225 (1964)]. Specifically, we derive the effective Bogoliubov-de Gennes equation, in which the self-energies due to the effective electron-electron interactions contribute to the singlet and triplet order parameters. It is further shown that for the singlet order parameter, it is efficiently suppressed due to this self-energy renormalization; whereas for the triplet order parameter, it is the $p$-wave ($p_x\pm ip_y$) one with the ${\bf d}$-vector parallel to the effective magnetic field due to the spin-orbit coupling. Finally, we perform the numerical calculation in InSb (100) quantum wells. Specifically, we reveal that the Coulomb interaction is much more important than the electron-phonon interaction at low temperature. Moreover, it shows that with proper electron density, the minimum of the renormalized singlet and the maximum of the induced triplet order parameters are comparable, and hence can be experimentally distinguished.

Optimized Novel Indium Antimonide Quantum Well Field Effect Transistor for High-Speed and Low Power Logic Applications

The physical gate length L G of the Si transistors are shrinking day by day to meet Moore’s law that states the number of transistors per integrated circuit doubles in every 24 months. It is projected that L G may be down to ~20 nm. Therefore, it is urgent need to be “energy efficient” which operates with the lowest switching power. Much effort has been paid to incorporate III-V nanoelectronics on the silicon platform due to highest intrinsic electron mobility. The InSb quantum well field effect transistor (QWFET) is a promising candidate for future high performance and low power logic applications [1,2]. In addition, recent success in depositing high-quality Al2O3 gate dielectrics by atomic layer deposition (ALD) on the InSb quantum wells (QWs) and completely depletion of the two-dimensional electron gas (2DEG) confined in InSb QW opens the prospects to fabricate high-quality InSb QW field effect transistor (FET) [3,4]. An InSb QWFET with a 10 nm thick Al2O3 top gate insulator has been simulated by using quantum corrected Schrödinger-Poisson (QCSP) solution as shown in Fig. 1 (a). Gate voltage (V g) dependent electron density (ns ) and mobility (µ) is shown in Fig. 1 (b). A very high electron mobility 4.42 m2V-1s-1 at V g= 0V is achieved which is at least ~180 times greater than that of Si NMOS. The confined 2DEG in InSb QW is completely depleted with a very small V g= -0.25V (is called as the pinch–off voltage, V p). The slope of the ns-Vg yields a giant gate controllability ratio of dn s/dV g = ~ 5.2 × 1015 m -2 V -1 (estimated in the range of V g=-0.2V to 0V). The room temperature conduction band (CB) and valance band (VB) profile of the proposed structure at V g= 0 and -0.25V are calculated by QCSP as shown in Fig. 2. The QW is lifted above the Fermi level (E F) at V g = -0.25V which is confirmed complete depletion (V p) as shown in Fig. 1. Moreover, the hole accumulation prevents as the VB doesn’t touch the E F. The interface trap density (D it) has been calculated using the equation D it= -(dQ it / (e × d(E F - E V))) where Q it is the net charge (difference between oxide and semiconductor charge) [4]. Energy dependent D it and corresponding applied gate voltage (V g) is shown in Fig. 3. Very low D it is found to be 7.8 × 1014 – 3.7 × 1016 m-2eV- 1 at the interface between Al2O3 and Al0.1In0.9Sb top layer of the InSb QWFET, results a giant dn s/dV g (Fig. 1b). It indicates that the E F is smoothly tuned by the V g due to a very low D it of the InSb QWFET. The capacitance-voltage (C-V) calculation has also been confirmed the low D it and V p of the proposed QWFET. The standard transistor characteristics with I D versus V DS at different V g, transconductance (g m) have also been calculated and explained by the established theory and experimental explanation. [1] T. Ashley et al. Proceedings 7th International Conference on Solid-State and Integrated Circuits Technology (SSICT), 2253 (2004). [2] S. Datta, Microelectronic Engineering84, 2133 (2007). [3] M. M. Uddin et al., Appl. Phys. Lett.101, 233503 (2012). [4] M. M. Uddin et al., Appl. Phys. Lett.103, 123502 (2013). Fig. 1: (a) Cross section of InSb optimized QWFET layer structure with LG =100 nm and δ-doping (dashed line). (b) Electron density (n s) and mobility (μ) of the InSb QWFET as a function of gate bias (V g) at 300 K. The dashed line points to the pinch-off voltage V p. Fig. 2: Band profile (CB and VB) of the proposed InSb QWFET at 300 K. The Fermi level is shown at 0eV. Fig. 3: The interface trap density (D it) as a function of E F-E V obtained from the QCSP solution with corresponding applied V g (V). Figure 1

Relationship between transport properties and band diagrams in InAsxSb1−x/Al0.1In0.9Sb quantum wells

The resistivity of InAs0.1Sb0.9/Al0.1In0.9Sb quantum wells (QWs) is much lower than that of InSb/Al0.1In0.9Sb QWs, staying low resistivity even at low temperature. Fundamental difference in low temperature transport properties between InSb/Al0.1In0.9Sb and InAs0.1Sb0.9/Al0.1In0.9Sb QWs was revealed, based on the band diagram calculations of these QWs. Band diagrams of InAsxSb1−x/Al0.1In0.9Sb QWs showed that the energy band of the InAsxSb1−x layer moves downward with increasing As content x. The QW is type I at x equal to 0, becomes type II at x equal to 0.1. The Fermi level (EF) of the InSb QWs lies in the band gap and below apart from the bottom of the conduction band, while EF of the InAs0.1Sb0.9 QWs is above the bottom of the conduction band of the well. The calculated sheet carrier densities are in good agreement with the experimental results. It well explains that the sheet carrier density difference between InSb and InAs0.1Sb0.9 QWs mainly originates from this band diagram difference and the position of EF.

Low temperature transport property of the InSb and InAsSb quantum wells with Al0.1In0.9Sb barrier layers grown by MBE

We investigated difference in the transport properties between Al0.1In0.9Sb/InSb and Al0.1In0.9Sb/InAs0.1Sb0.9 quantum wells (QWs). The resistivity of InSb QWs increases exponentially with decreasing temperature, while that of InAs0.1Sb0.9 QWs is much lower than that of InSb QWs, showing low resistivity even at low temperature. Energy band diagram calculations of InAsxSb1−x/Al0.1In0.9Sb quantum wells (QWs) revealed that the bottom of the conduction band of the InAsxSb1−x well moves downward with increasing As content x. The bottom of the InSb QWs lies above the Fermi level (EF), resulting in depletion of the QW, while that in InAs0.1Sb0.9 QWs lies under EF at low temperature. These calculation results support the experimental difference of the resistivity and sheet carrier density between two types of the QWs well.

Improved electron transport properties of InSb quantum well structure using stepped buffer layer for strain reduction

We investigated a high-quality novel AlInSb buffer layer to increase the electron mobility of an InSb quantum well (QW) structure, which was grown on a (100) GaAs substrate by molecular beam epitaxy. We achieved high electron mobility in the InSb QW structure using an Al0.25In0.75Sb/Al0.15In0.85Sb stepped buffer layer and realized reduced compressive strain and improved surface roughness. In addition, we investigated the dependence of the Al0.25In0.75Sb layer thickness in the Al0.25In0.75Sb/Al0.15In0.85Sb stepped buffer layer on the electron mobility characteristics. We only obtained increased electron mobility using the Al0.25In0.75Sb layer within a critical thickness range.

Interfacial trap states and improvement of low-temperature mobility by doping in InSb/AlInSb quantum wells

The effect of doping on InSb/Al0.1In0.9Sb quantum wells (QWs) was investigated, and it was found that doping improves the electron mobility at low temperatures and leads to a weaker dependence of the resistivity with temperature. The dependence of the carrier density on the well width revealed trap states at the interfaces of the QW whose sheet density per interface was estimated to be about 4 × 1010 cm−2. The low mobility of undoped InSb QWs, in particular, at low temperature seems to have been caused by positively ionized impurity scattering at the interfacial trap states. Doping compensates for the trap states and enhances mobility by suppressing ionized impurity scattering. Thus, intentional doping is necessary for developing high-mobility InSb QW devices. The origin of the trap states is qualitatively discussed.

Step graded buffer for (110) InSb quantum wells grown by molecular beam epitaxy

We report on a two step buffer layer preparation for the growth of InSb quantum wells on a (110) GaAs surface. At each buffer layer step, layer conditions were optimized to produce smooth surfaces compatible with InSb quantum wells. Through varying growth rate, group V/III flux ratio, substrate temperature, and the addition of in situ annealing, we are able to grow In0.85Al0.15Sb on a GaAs substrate with an RMS surface roughness of approximately 2nm. Surface morphology and cross-sectional transmission electron microscopy (TEM) were analyzed to understand the formation of threading dislocations, inclusions and dislocation filtering. This work presents an initial study for the growth of large lattice mismatched III-V materials on the (110) surface.

High electron mobility in InSb epilayers and quantum wells grown with AlSb nucleation on Ge-on-insulator substrates

InSb epilayers and InSb/Al0.20In0.80Sb quantum wells (QWs) were grown on 4°-off-axis Ge-on-insulator (GeOI) substrates by molecular beam epitaxy. An initial AlSb nucleation was found to be important for achieving good crystalline quality. For a 4.0-μm-thick InSb epilayer and 25-nm-thick InSb QW, the room-temperature (RT) electron mobility was increased by 25% and 60% [58 000 cm2/(V-s) for the epilayer and 24 000 cm2/(V-s) for the QW], respectively, by using an off-axis GeOI substrate instead of an on-axis GeOI (001) substrate. This significant improvement may be attributed to the reduction of antiphase domains, microtwins, and threading dislocations. A modified QW structure on a 4°-off-axis GeOI substrate showed a further 25% improvement in RT electron mobility with a value 32 000 cm2/(V-s). This is the highest RT electron mobility in an InSb QW grown on a Ge-based substrate to date.