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Superconductor-ferromagnet interfaces in two-dimensional heterostructures present a unique opportunity to study the interplay between superconductivity and ferromagnetism. The realization of such nanoscale heterostructures in van der Waals (vdW) crystals remains largely unexplored due to the challenge of making atomically-sharp interfaces from their layered structures. Here, we build a vdW ferromagnetic Josephson junction (JJ) by inserting a few-layer ferromagnetic insulator Cr2Ge2Te6 into two layers of superconductor NbSe2. The critical current and corresponding junction resistance exhibit a hysteretic and oscillatory behavior against in-plane magnetic fields, manifesting itself as a strong Josephson coupling state. Also, we observe a central minimum of critical current in some JJ devices as well as a nontrivial phase shift in SQUID structures, evidencing the coexistence of 0 and π phase in the junction region. Our study paves the way to exploring sensitive probes of weak magnetism and multifunctional building-blocks for phase-related superconducting circuits using vdW heterostructures., The superconductor-ferromagnet interface provides a unique opportunity to study the interplay between superconductivity and ferromagnetism. Here, the authors build a van der Waals ferromagnetic Josephson junction evidencing a strong 0 and π phase Josephson coupling.

Symmetry manipulation can be used to effectively tailor the physical order in solid-state systems. With the breaking of both the inversion and time-reversal symmetries, nonreciprocal magneto-transport may arise in nonmagnetic systems to enrich spin-orbit effects. Here, the observation of unidirectional magnetoresistance (UMR) in lattice-matched InSb/CdTe films is investigated up to room temperature. Benefiting from the strong built-in electric field of 0.13 V nm

The interplay between quenched disorder and critical behavior in quantum phase transitions is conceptually fascinating and of fundamental importance for understanding phase transitions. However, it is still unclear whether or not the quenched disorder influences the universality class of quantum phase transitions. More crucially, the absence of superconducting-metal transitions under in-plane magnetic fields in 2D superconductors imposes constraints on the universality of quantum criticality. Here, we observe the thickness-tuned universality class of superconductor-metal transition by changing the disorder strength in β - W films with varying thickness. The finite-size scaling uncovers the switch of universality class: quantum Griffiths singularity to multiple quantum criticality at a critical thickness of t c ⊥ 1 ~ 8 n m and then from multiple quantum criticality to single criticality at t c ⊥ 2 ~ 16 n m . Moreover, the superconducting-metal transition is observed for the first time under in-plane magnetic fields and the universality class is changed at t c ‖ ~ 8 n m . The observation of thickness-tuned universality class under both out-of-plane and in-plane magnetic fields provides broad information for the disorder effect on superconducting-metal transitions and quantum criticality.

The study of high dielectric materials has received great attention lately as a key passive component for the application of metal-insulator-metal (MIM) capacitors. In this paper, 50 nm thick Al2O3 thin films have been prepared by atomic layer deposition technique on indium tin oxide (ITO) pre-coated glass substrates and titanium nitride (TiN) coated Si substrates with typical MIM capacitor structure. Photolithography and metal lift-off technique were used for processing of the MIM capacitors. Semiconductor Analyzer with probe station was used to perform capacitance-voltage (C-V) characterization with low-medium frequency range. Current-voltage (I-V) characteristics of MIM capacitors were measured on precision source/measurement system. The performance of Al2O3 films of MIM capacitors on glass was examined in the voltage range from −5 to 5 V with a frequency range from 10 kHz to 5 MHz. Au/Al2O3/ITO/Glass MIM capacitors demonstrate a capacitance density of 1.6 fF/μm2at 100 kHz, a loss tangent ~0.005 at 100 kHz and a leakage current of 1.79 × 10−8 A/cm2 at 1 MV/cm (5 V) at room temperature. Au/Al2O3/TiN/Si MIM capacitors demonstrate a capacitance density of 1.5 fF/μm2 at 100 kHz, a loss tangent ~0.007 at 100 kHz and a lower leakage current of 2.93 × 10−10 A/cm2 at 1 MV/cm (5 V) at room temperature. The obtained electrical properties could indicate a promising application of MIM Capacitors.

Spin-orbit coupling (SOC), the relativistic effect describing the interaction between the orbital and spin degrees of freedom, provides an effective way to tailor the spin/magnetic orders using electrical means. Here, we report the manipulation of the spin-orbit interaction in the lattice-matched InSb/CdTe heterostructures. Owing to the energy band bending at the heterointerface, the strong Rashba effect is introduced to drive the spin precession where pronounced weak antilocalization cusps are observed up to 100 K. With effective quantum confinement and suppressed bulk conduction, the SOC strength is found to be enhanced by 75% in the ultrathin InSb/CdTe film. Most importantly, we realize the electric-field control of the interfacial Rashba effect using a field-effect transistor structure and demonstrate the gate-tuning capability which is 1-2 orders of magnitude higher than other materials. The adoption of the InSb/CdTe integration strategy may set up a general framework for the design of strongly spin-orbit coupled systems that are essential for CMOS-compatible low-power spintronics.

Topological nodal-line semimetals (TNLSMs) are materials whose conduction and valence bands cross each other, meeting a topologically protected closed loop rather than discrete points in the Brillouin zone (BZ). The anticipated properties for TNLSMs, include drumhead-like nearly flat surface states, unique Landau energy levels, special collective modes, long-range Coulomb interactions, or the possibility of realizing high-temperature superconductivity. Recently, SrAs3 has been theoretically proposed and then experimentally confirmed to be a TNLSM. Here, we report high-pressure experiments on SrAs3, identifying a Lifshitz transition below 1 GPa and a superconducting transition accompanied by a structural phase transition above 20 GPa. A topological crystalline insulator (TCI) state is revealed by means of density functional theory (DFT) calculations on the emergent high-pressure phase. As the counterpart of topological insulators, TCIs possess metallic boundary states protected by crystal symmetry, rather than time reversal. In consideration of topological surface states (TSSs) and helical spin texture observed in the high-pressure state of SrAs3, the superconducting state may be induced in the surface states, and is most likely topologically nontrivial, making pressurized SrAs3 a strong candidate for topological superconductor.

We report the study of current-induced magnetization switching in the Ta/CoFeB heterostructures by simultaneous magneto-electrical transport and magneto-optical Kerr effect (MOKE) microscopy measurements. Although the anomalous Hall hysteresis loop summarizes the general switching behaviors, the supplementary MOKE data can provide spatial and temporal information to visualize the magnetic domain evolution as functions of the applied current and the in-plane magnetic field. More importantly, when the initial magnetic field is not sufficient enough, the interfacial Dzyaloshinskii–Moriya interaction (DMI) would modulate the spin-orbit torque (SOT) current switching dynamics and lead to the formation of the intermediate Hall resistance plateau with meta-stable tilted domain texture. Our work elucidates the importance of the applied in-plane field and unveils an effective approach to investigate the SOT/DMI-related phenomena in symmetry-breaking magnetic heterostructures.

This paper presents experimental characterizations and device modeling on the nanoscale MOSFETs with 40 nm low-power CMOS technology. Systematic temperature-dependent ${I}_{D}$ - ${V}_{GS}$ results of NMOS/PMOS devices reveal that both the threshold voltage and the effective channel mobility exhibit strong correlations with the device size owning to the depletion region broadening around the gate channel at cryogenic temperatures. By taking the temperature-driven gate geometry effects into consideration, a generic physical model with universal fitting parameters is proposed to depict the transfer characteristics of all CMOS transistors across the device size chart, and further validations of the modified BSIM compact model might pave the way for an accurate design of cryogenic electronics applications.

The intrinsic magnetic topological insulator MnBi2Te4 (MBT) has provided a platform for the successful realization of exotic quantum phenomena. To broaden the horizons of MBT-based material systems, we intercalate ferromagnetic MnTe layers to construct the [(MBT)(MnTe)m]N superlattices by molecular beam epitaxy. The effective incorporation of ferromagnetic spacers mediates the anti-ferromagnetic interlayer coupling among the MBT layers through the exchange spring effect at the MBT/MnTe hetero-interfaces. Moreover, the precise control of the MnTe thickness enables the modulation of relative strengths among the constituent magnetic orders, leading to tunable magnetoelectric responses, while the superlattice periodicity serves as an additional tuning parameter to tailor the spin configurations of the synthesized multi-layers. Our results demonstrate the advantages of superlattice engineering for optimizing the magnetic interactions in MBT-family systems, and the ferromagnet-intercalated strategy opens up new avenues in magnetic topological insulator structural design and spintronic applications., 20 pages, 5 figures

The quantized version of anomalous Hall effect realized in magnetic topological insulators (MTIs) has great potential for the development of topological quantum physics and low-power electronic/spintronic applications. To enable dissipationless chiral edge conduction at zero magnetic field, effective exchange field arisen from the aligned magnetic dopants needs to be large enough to yield specific spin sub-band configurations. Here we report the thickness-tailored quantum anomalous Hall (QAH) effect in Cr-doped (Bi,Sb)2Te3 thin films by tuning the system across the two-dimensional (2D) limit. In addition to the Chern number-related metal-to-insulator QAH phase transition, we also demonstrate that the induced hybridization gap plays an indispensable role in determining the ground magnetic state of the MTIs, namely the spontaneous magnetization owning to considerable Van Vleck spin susceptibility guarantees the zero-field QAH state with unitary scaling law in thick samples, while the quantization of the Hall conductance can only be achieved with the assistance of external magnetic fields in ultra-thin films. The modulation of topology and magnetism through structural engineering may provide a useful guidance for the pursuit of QAH-based new phase diagrams and functionalities., Comment: 22 pages, 4 figures

Quantum well states (QWSs) can form at the surface or interfaces of materials with confinement potential. They have broad applications in electronic and optical devices such as high mobility electron transistor, photodetector and quantum well laser. The properties of the QWSs are usually the key factors for the performance of the devices. However, direct visualization and manipulation of such states are in general challenging. In this work, by using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy/spectroscopy (STM/STS), we directly probe the QWSs generated on the vacuum interface of a narrow band gap semiconductor Nb2SiTe4. Interestingly, the position and splitting of QWSs could be easily manipulated via potassium (K) dosage onto the sample surface. Our results suggest Nb2SiTe4 to be an intriguing semiconductor system to study and engineer the QWSs, which has great potential in device applications., Comment: 28 pages, 5 figures

Quantum well states (QWSs) can form at the surface or interfaces of materials with confinement potential. They have broad applications in electronic and optical devices such as high mobility electron transistor, photodetector, and quantum well laser. The properties of the QWSs are usually the key factors for the performance of the devices. However, direct visualization and manipulation of such states are, in general, challenging. In this work, by using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy/spectroscopy (STM/STS), we directly probe the QWSs generated on the vacuum interface of a narrow band gap semiconductor Nb

Mechanically exfoliated two-dimensional ferromagnetic materials (2D FMs) possess long-range ferromagnetic order and topologically nontrivial skyrmions in few layers. However, because of the dimensionality effect, such few-layer systems usually exhibit much lower Curie temperature (TC) compared to their bulk counterparts. It is therefore of great interest to explore effective approaches to enhance their TC, particularly in wafer-scale for practical applications. Here, we report an interfacial proximity-induced high-TC 2D FM Fe3GeTe2 (FGT) via A-type antiferromagnetic material CrSb (CS) which strongly couples to FGT. A superlattice structure of (FGT/CS)n, where n stands for the period of FGT/CS heterostructure, has been successfully produced with sharp interfaces by molecular-beam epitaxy on 2-inch wafers. By performing elemental specific X-ray magnetic circular dichroism (XMCD) measurements, we have unequivocally discovered that TC of 4-layer Fe3GeTe2 can be significantly enhanced from 140 K to 230 K because of the interfacial ferromagnetic coupling. Meanwhile, an inverse proximity effect occurs in the FGT/CS interface, driving the interfacial antiferromagnetic CrSb into a ferrimagnetic state as evidenced by double-switching behavior in hysteresis loops and the XMCD spectra. Density functional theory calculations show that the Fe-Te/Cr-Sb interface is strongly FM coupled and doping of the spin-polarized electrons by the interfacial Cr layer gives rise to the TC enhancement of the Fe3GeTe2 films, in accordance with our XMCD measurements. Strikingly, by introducing rich Fe in a 4-layer FGT/CS superlattice, TC can be further enhanced to near room temperature. Our results provide a feasible approach for enhancing the magnetic order of few-layer 2D FMs in wafer-scale and render opportunities for realizing realistic ultra-thin spintronic devices., Utilizing proximity effect, we realize an effective and reliable approach to accomplish near-room-temperature (286.7 K) ferromagnetic order and double switching behavior in wafer-scale 4-layer-Fe3GeTe2/1.6-nm-CrSb superlattice.

The completion of quantum Hall trio, namely the quantum Hall effect (QHE), the quantum spin Hall effect (QSHE), and the quantum anomalous Hall effect (QAHE), has greatly broadened our understandings about the electron movement in solids. Likewise, the discovered scale-invariant dissipationless conduction in these three quantum transport states has inspired us to the development of practical low-power-consumption electronics/spintronics applications. In this review article, we outline the fundamental physics and relations between different Hall effects. In general, QSHE is a result of band inversion due to the large spin-orbit coupling; since the time-reversal symmetry (TRS) is well-protected in such QSH insulators, helical edge states with both spin-up and spin-down electrons are allowed and the conduction is immune to non-magnetic impurities. On the other hand, when TRS is broken by either perpendicular magnetic field or magnetic order, helical edge states are reduced to the single chiral channel, which in turn gives rise to QHE and QAHE, and backscattering from any impurity is strictly forbidden owing to the nature of chirality. Moreover, the interplay between this quantum Hall trio in certain conditions unveils new ways to explore emerging chiral materials and related quantum phenomena.

This paper presents the temperature-dependent characterizations and compact modeling on both the front-end-of-line (FEOL) and back-end-of-line (BEOL) devices based on the HLMC 40-nm low-power CMOS technology. Moreover, an EDA-compatible cryo-CMOS platform which covers the 10 $\mathrm{K} region is developed to guide the design of specific cryogenic integrated circuits for quantum computing applications.

The combination of magnetism and topology in magnetic topological insulators (MTIs) has led to unprecedented advancements of time reversal symmetry-breaking topological quantum physics in the past decade. Compared with the uniform films, the MTI heterostructures provide a better framework to manipulate the spin-orbit coupling and spin properties. In this review, we summarize the fundamental mechanisms related to the physical orders host in (Bi,Sb)2(Te,Se)3-based hybrid systems. Besides, we provide an assessment on the general strategies to enhance the magnetic coupling and spin-orbit torque strength through different structural engineering approaches and effective interfacial interactions. Finally, we offer an outlook of MTI heterostructures-based spintronics applications, particularly in view of their feasibility to achieve room-temperature operation., 33 pages, 11 figures

High-magnetic-field transport measurements and ab initio calculations on the layered superconductor TaSe3 have provided evidence for the existence of a three-dimensional strong topological state. Longitudinal magnetotransport measurements up to similar to 33 T unveiled striking Shubnikov-de Haas oscillations with two fundamental frequencies at 100 and 175 T corresponding to a nontrivial hole Fermi pocket at the Gamma point and a nontrivial electron Fermi pocket at the B point, respectively, in the Brillouin zone. However, calculations revealed one more electron pocket at the B point which was not detected by the magnetotransport measurements, presumably due to the limited carrier momentum relaxation time. Angle-dependent quantum oscillations by rotating the sample with respect to the magnetic field revealed clear changes in the two fundamental frequencies, indicating anisotropic electronic Fermi pockets. The ab initio calculations gave the topological Z(2) invariant of (1; 100) and revealed a single Dirac cone on the (1 0 -1) surface at the (X) over bar point with helical spin texture at a constant energy contour, suggesting a strong topological state. The results demonstrate TaSe3 as an excellent platform to study the interplay between the topological phase and superconductivity and a promising system for the exploration of topological superconductivity.

Integration of a quantum anomalous Hall insulator with a magnetically ordered material provides an additional degree of freedom through which the resulting exotic quantum states can be controlled. Here, an experimental observation is reported of the quantum anomalous Hall effect in a magnetically-doped topological insulator grown on the antiferromagnetic insulator Cr2 O3 . The exchange coupling between the two materials is investigated using field-cooling-dependent magnetometry and polarized neutron reflectometry. Both techniques reveal strong interfacial interaction between the antiferromagnetic order of the Cr2 O3 and the magnetic topological insulator, manifested as an exchange bias when the sample is field-cooled under an out-of-plane magnetic field, and an exchange spring-like magnetic depth profile when the system is magnetized within the film plane. These results identify antiferromagnetic insulators as suitable candidates for the manipulation of magnetic and topological order in topological insulator films.

Engineering the anomalous Hall effect (AHE) in the emerging magnetic topological insulators (MTIs) has great potentials for quantum information processing and spintronics applications. In this letter, we synthesize the epitaxial Bi2Te3/MnTe magnetic heterostructures and observe pronounced AHE signals from both layers combined together. The evolution of the resulting hybrid AHE intensity with the top Bi2Te3 layer thickness manifests the presence of an intrinsic ferromagnetic phase induced by the topological surface states at the heterolayer-interface. More importantly, by doping the Bi2Te3 layer with Sb, we are able to manipulate the sign of the Berry phase-associated AHE component. Our results demonstrate the un-paralleled advantages of MTI heterostructures over magnetically doped TI counterparts, in which the tunability of the AHE response can be greatly enhanced. This in turn unveils a new avenue for MTI heterostructure-based multifunctional applications., Comment: 20 pages, 4 figures

We demonstrate spin-orbit torque (SOT) switching of amorphous CoTb single layer films with perpendicular magnetic anisotropy (PMA). The switching sustains even the film thickness is above 10 nm, where the critical switching current density keeps almost constant. Without the need of overcoming the strong interfacial Dzyaloshinskii-Moriya interaction caused by the heavy metal, a quite low assistant field of ~20 Oe is sufficient to realize the fully switching. The SOT effective field decreases and undergoes a sign change with the decrease of the Tb-concentration, implying that a combination of the spin Hall effect from both Co and Tb as well as an asymmetric spin current absorption accounts for the SOT switching mechanism. Our findings would advance the use of magnetic materials with bulk PMA for energy-efficient and thermal-stable non-volatile memories, and add a different dimension for understanding the ordering and asymmetry in amorphous thin films., Comment: 17 pages, 4 figures, Phys. Rev. B 101, 214418 (2020)

Incorporating ferromagnetic dopants into three-dimensional topological insulator thin films has recently led to the realisation of the quantum anomalous Hall effect. These materials are of great interest since they may support electrical currents that flow without resistance, even at zero magnetic field. To date, the quantum anomalous Hall effect has been investigated using low-frequency transport measurements. However, transport results can be difficult to interpret due to the presence of parallel conductive paths, or because additional non-chiral edge channels may exist. Here we move beyond transport measurements by probing the microwave response of a magnetised disk of Cr-(Bi,Sb)2Te3. We identify features associated with chiral edge plasmons, a signature that robust edge channels are intrinsic to this material system. Our results provide a measure of the velocity of edge excitations without contacting the sample, and pave the way for an on-chip circuit element of practical importance: the zero-field microwave circulator., Direct measurement of edge transport in the quantum anomalous Hall effect can be made difficult due to the presence of parallel conductive paths. Here, Mahoney et al. report features associated with chiral edge plasmons, a signature of robust edge states, by probing the zero-field microwave response of a magnetised disk of Cr-(Bi,Sb)2Te3.

The realization and application of spintronic devices would be dramatically advanced if room-temperature ferromagnetism could be integrated into semiconductor nanostructures, especially when compatible with mature silicon technology. Herein, we report the observation of such a system – an Si/MnGe superlattice with quantum dots well aligned in the vertical direction successfully grown by molecular beam epitaxy. Such a unique system could take full advantage of the type-II energy band structure of the Si/Ge heterostructure, which could trap the holes inside MnGe QDs, significantly enhancing the hole-mediated ferromagnetism. Magnetic measurements indeed found that the superlattice structure exhibited a Curie temperature of above 400 K. Furthermore, zero-field cooling and field cooling curves could confirm the absence of ferromagnetic compounds, such as Ge8Mn11 (Tc ∼ 270 K) and Ge3Mn5 (Tc ∼ 296 K) in our system. Magnetotransport measurement revealed a clear magnetoresistance transition from negative to positive and a pronounced anomalous Hall effect. Such a unique Si/MnGe superlattice sets a new stage for strengthening ferromagnetism due to the enhanced hole-mediation by quantum confinement, which can be exploited for realizing the room-temperature Ge-based spin field-effect transistors in the future.

The low occurring temperature of quantum anomalous Hall effect is a result of weak ferromagnetism and trivial band involvement., Quantum anomalous Hall effect has been observed in magnetically doped topological insulators. However, full quantization, up until now, is limited within the sub–1 K temperature regime, although the material’s magnetic ordering temperature can go beyond 100 K. Here, we study the temperature limiting factors of the effect in Cr-doped (BiSb)2Te3 systems using both transport and magneto-optical methods. By deliberate control of the thin-film thickness and doping profile, we revealed that the low occurring temperature of quantum anomalous Hall effect in current material system is a combined result of weak ferromagnetism and trivial band involvement. Our findings may provide important insights into the search for high-temperature quantum anomalous Hall insulator and other topologically related phenomena.

Tetradymite-type Bi2X3 (X = Se, Te, Sb) systems have been used as the best thermoelectric materials for decades. Recently, such V-VI compound materials have attracted immense interests because they are identified as topological insulators with salient features associated with the unique topological surface states. In this chapter, we review the use of molecular beam epitaxy technique to achieve single-crystalline Bi2X3 thin films with atomically smooth surface and extremely low-defect density. In particular, we will explore the unique van der Waals epitaxy growth mechanism, providing detailed discussions on the choice of key growth procedures and parameters during the MBE growth. Furthermore, we will introduce advanced growth techniques such as functional doping and structural engineering so that the functionalities can be further multiplied. Finally, we will give an outlook on Bi2X3-based materials system for exploring new physics and device applications.

We report the temperature dependence of the spin–orbit torque (SOT) in the in situ grown Bi2Te3/MnTe heterostructures by molecular beam epitaxy. By appropriately designing the film stack, robust ferromagnetic order with high Curie temperature and strong perpendicular magnetic anisotropy is established in the MnTe layer. Meanwhile, the sharp hetero-interface warrants highly efficient spin current injection from the conductive topological insulator (TI) channel. Accordingly, SOT-driven magnetization switching is observed up to 90 K with the critical current density within the 106 A⋅cm−2 range. More importantly, the temperature-dependent harmonic measurement data can be divided into two categories, namely, the spin Hall effect of the TI bulk states gives rise to a relatively small spin Hall angle in the high-temperature region, whereas the spin-momentum locking nature of the interfacial Dirac fermions leads to the enhancement of the SOT strength once the topological surface states become the dominant conduction channel at deep cryogenic temperatures. Our results offer direct evidence of the underlying mechanism that determines the SOT efficiency and may set up a suitable platform to realize TI-based spin–orbit applications toward room temperature.

Magnetic topological insulators such as Cr-doped (Bi,Sb)2Te3 provide a platform for the realization of versatile time-reversal symmetry-breaking physics. By constructing heterostructures with N\'eel order in an antiferromagnetic CrSb and magnetic topological order in Cr-doped (Bi,Sb)2Te3, we realize emergent interfacial magnetic phenomena which can be tailored through artificial structural engineering. Through deliberate geometrical design of heterostructures and superlattices, we demonstrate the use of antiferromagnetic exchange coupling in manipulating the magnetic properties of the topological surface massive Dirac fermions. This work provides a new framework on integrating topological insulators with antiferromagnetic materials and unveils new avenues towards dissipationless topological antiferromagnetic spintronics., Comment: 25 pages, 4 figures

Spintronics is regarded as a promising solution for resolving the major challenging issues related to the scaling of Si-based complementary metal–oxide–semiconductor (CMOS) technology as it offers the advantages of combing the spin and charge degrees of freedom. After decades of progress, the quintessence to achieve practical low-dissipation applications lies in the ability to manipulate magnetic states by electric field via several different physical mechanisms. Among them, the emergence of the spin-orbit coupling engineering has been shown to dramatically reduce energy dissipation and improve the performance as well as to multiply spintronic device possibilities and functionalities for a new generation of ultralow-power nonvolatile spintronic systems. This article provides a review of the current development including fundamental physics and experimental implementations of electric-field-controlled ferromagnetism in dilute magnetic semiconductors, voltage control of magnetic anisotropy, spin-orbit-torque-assisted magnetization switching, and antiferromagnetic (AFM) material-based spin-orbitronic systems. We provide an assessment in terms of scaling of energy, speed, and size. Finally, we offer an outlook of electric-field-controlled spintronic applications, particularly in view of their integration with CMOS to form hybrid spintronic circuits.

In this work, an InxGa1−xAsySb1−y quaternary alloy with a vertical distribution of type-II InAs/GaSb superlattices is grown in the miscibility gap using a fractional monolayer alloy (FMA) process on a vicinal surface. X-ray diffraction patterns indicate that InxGa1−xAsySb1−y quaternary alloys with high In contents (up to 50%–65%) still maintain pure phases and good crystal quality. Transmission electron microscopy with energy-dispersive spectroscopy is used to confirm the constituent elements of the quaternary alloy. In addition, a significant strain distribution phenomenon parallel to the growth direction (ϵxx) can be observed in the quaternary alloy using strain maps and related strain profiles. The mean strain peak values are close to those of conventional planar superlattices, including InAs/GaSb and InAs/InAsSb. Photoluminescence measurements and k∙p model calculations show that the vertical type-II InAs/GaSb superlattice distribution may generate a unique bandgap in the quaternary alloy by manipulating the FMA process on the vicinal surface. The quaternary alloy components and vertically-distributed superlattice parameters can be regulated, and the quaternary alloy bandgap can cover the mid-to long-wavelength infrared regions. This work offers an effective route to solve the miscibility problem and use neoteric quaternary alloys with carrier emission from the unique bandgap for infrared optoelectronic devices.

We report the growth of InSb/CdTe hetero-epitaxial thin films on the GaAs (111)B substrate using molecular beam epitaxy. The use of (111) orientation enables the fast strain relaxation during the CdTe buffer layer growth, and major crystallographic defects are confined near the CdTe/GaAs interface. Owing to the lattice matching between InSb and CdTe, layer-by-layer 2D growth of InSb is observed from the initial growth stage. Both smooth surface morphology and low defect density of the as-grown InSb/CdTe heterostructures give rise to the enhancement of electron mobility when the InSb layer thickness is reduced below 30 nm as compared to the InSb/GaAs counterparts. The integration of InSb/CdTe highlights the advantage of lattice-matched epitaxial growth and provides a promising approach to design high-quality III–V/II–VI hybrid systems for high-performance device applications.