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Solid-state batteries (SSBs) have attracted considerable attention due to the high intrinsic stability and theoretical energy density. As the core part, garnet electrolyte has been extensively investigated due to high lithium-ion conductivity, wide electrochemical potential window, and easy synthesis. However, the poor and electrochemically unstable interfacial contact between electrolyte and lithium anode greatly impedes the practical use of garnet based SSBs. Here, we report such interface challenge can be perfectly tackled by introducing a multifunctional Li0.3La0.5TiO3 (LLTO) as additive into lithium anode. The limited reaction between the LLTO and lithium effectively changes the physical properties of lithium anode, making it perfectly compatible with garnet surface, consequently significantly decreasing the interfacial resistant from 200 to only 48 Ω cm2 and greatly improving the interface stability and avoiding the dendrite formation. Interestingly, LLTO provides additional lithium storage, and the close interface contact and the high lithium-ion conductivity of LLTO ensures high-rate performance. Consequently, the symmetrical cell runs stably at 0.1 mA cm-2 for 400 h without obvious degradation. The assembled SSB with the LiFePO4 cathode and Li-LLTO composite anode demonstrates a specific capacity of 147 mAh g-1 and remarkable cycling stability with only 10 % capacity decay over 700 cycles at 1 C.

Phosphorus atoms in silicon offer a rich quantum computing platform where both nuclear and electron spins can be used to store and process quantum information. While individual control of electron and nuclear spins has been demonstrated, the interplay between them during qubit operations has been largely unexplored. This study investigates the use of exchange-based operation between donor bound electron spins to probe the local magnetic fields experienced by the qubits with exquisite precision at the atomic scale. To achieve this, coherent exchange oscillations are performed between two electron spin qubits, where the left and right qubits are hosted by three and two phosphorus donors, respectively. The frequency spectrum of exchange oscillations shows quantized changes in the local magnetic fields at the qubit sites, corresponding to the different hyperfine coupling between the electron and each of the qubit-hosting nuclear spins. This ability to sense the hyperfine fields of individual nuclear spins using the exchange interaction constitutes a unique metrology technique, which reveals the exact crystallographic arrangements of the phosphorus atoms in the silicon crystal for each qubit. The detailed knowledge obtained of the local magnetic environment can then be used to engineer hyperfine fields in multi-donor qubits for high-fidelity two-qubit gates.

Silicon-based microelectronics technology is extremely mature, yet this profoundly important material is now also poised to become a foundation for quantum information processing technologies. In this article, we review the properties of silicon that have made it the material of choice for semiconductor-based qubits with an emphasis on the role that modeling and simulation have played in understanding and quantifying these properties. We also address some of the challenges that remain for silicon qubits for which modeling can play an important role and we offer our perspective on the future of this technology.

Electrically addressing spin systems is predicted to be a key component in developing scalable semiconductor-based quantum processing architectures, to enable fast spin qubit manipulation and long-distance entanglement via microwave photons. However, single spins have no electric dipole, and therefore a spin-orbit mechanism must be integrated in the qubit design. Here, we propose to couple microwave photons to atomically precise donor spin qubit devices in silicon using the hyperfine interaction intrinsic to donor systems and an electrically-induced spin-orbit coupling. We characterise a one-electron system bound to a tunnel-coupled donor pair (1P-1P) using the tight-binding method, and then estimate the spin-photon coupling achievable under realistic assumptions. We address the recent experiments on double quantum dots (DQDs) in silicon and indicate the differences between DQD and 1P-1P systems. Our analysis shows that it is possible to achieve strong spin-photon coupling in 1P-1P systems in realistic device conditions without the need for an external magnetic field gradient.

Germanium is typically used for solid-state electronics, fiber-optics, and infrared applications, due to its semiconducting behavior at optical and infrared wavelengths. In contrast, here we show that the germanium displays metallic nature and supports propagating surface plasmons in the deep ultraviolet (DUV) wavelengths, that is typically not possible to achieve with conventional plasmonic metals such as gold, silver, and aluminum. We measure the photonic band spectrum and distinguish the plasmonic excitation modes: bulk plasmons, surface plasmons, and Cherenkov radiation using a momentum-resolved electron energy loss spectroscopy. The observed spectrum is validated through the macroscopic electrodynamic electron energy loss theory and first-principles density functional theory calculations. In the DUV regime, intraband transitions of valence electrons dominate over the interband transitions, resulting in the observed highly dispersive surface plasmons. We further employ these surface plasmons in germanium to design a DUV radiation source based on the Smith-Purcell effect. Our work opens a new frontier of DUV plasmonics to enable the development of DUV devices such as metasurfaces, detectors, and light sources based on plasmonic germanium thin films.

Non-adiabatic quantum effects, often experimentally observed in semiconductors nano-devices such as single-electron pumps operating at high frequencies, can result in undesirable and uncontrollable behaviour. However, when combined with the valley degree of freedom inherent to silicon, these unfavourable effects may be leveraged for quantum information processing schemes. By using an explicit time evolution of the Schrodinger equation, we study numerically non-adiabatic transitions between the two lowest valley states of an electron in a quantum dot formed in a SiGe/Si heterostructure. The presence of a single atomic layer step at the top SiGe/Si interface opens an anti-crossing in the electronic spectrum as the centre of the quantum dot is varied. We show that an electric field applied perpendicularly to the interface allows tuning of the anti-crossing energy gap. As a result, by moving the electron through this anti-crossing, and by electrically varying the energy gap, it is possible to electrically control the probabilities of the two lowest valley states., 14 pages, 13 figures

Large-scale arrays of quantum-dot spin qubits in Si/SiGe quantum wells require large or tunable energy splittings of the valley states associated with degenerate conduction band minima. Existing proposals to deterministically enhance the valley splitting rely on sharp interfaces or modifications in the quantum well barriers that can be difficult to grow. Here, we propose and demonstrate a new heterostructure, the "Wiggle Well," whose key feature is Ge concentration oscillations inside the quantum well. Experimentally, we show that placing Ge in the quantum well does not significantly impact our ability to form and manipulate single-electron quantum dots. We further observe large and widely tunable valley splittings, from 54 to 239 ueV. Tight-binding calculations, and the tunability of the valley splitting, indicate that these results can mainly be attributed to random concentration fluctuations that are amplified by the presence of Ge alloy in the heterostructure, as opposed to a deterministic enhancement due to the concentration oscillations. Quantitative predictions for several other heterostructures point to the Wiggle Well as a robust method for reliably enhancing the valley splitting in future qubit devices., Main text and supplemental information, 11 pages, 7 figures

Silicon is a leading qubit platform thanks to the exceptional coherence times that can be achieved and to the available commercial manufacturing platform for integration. Building scalable quantum processing architectures relies on accurate quantum state manipulation, which can only be achieved through a complete understanding of the underlying quantum state properties. This article reviews the electrical methods that have been developed to probe the quantum states encoded in individual and interacting atom qubits in silicon, from the pioneering single electron tunneling spectroscopy framework in nanoscale transistors, to radio frequency reflectometry to probe coherence properties and scanning tunneling microscopy to directly image the wave function at the atomic scale. Together with the development of atomistic simulations of realistic devices, these methods are today applied to other emerging dopant and optically addressable defect states to accelerate the engineering of quantum technologies in silicon., An edited version of this manuscript will appear in MRS Bulletin

Being fundamentally limited to a current–voltage steepness of 60mV/dec, MOSFETs struggle to operate below 0.6 V. Further reduction in ${V}_{\text {DD}}$ and, consequently, power consumption can be achieved with novel devices, such as tunneling transistors (TFETs) that can overcome this limitation. TFETs, however, face challenges with low ON-current leading to slow performance. TFETs made from III-nitride heterostructures are quite promising in this regard. The lattice mismatch induces a piezoelectric polarization field in a nitride heterojunction that can boost the ON-current. However, it is shown here that the carrier thermalization at the heterointerface degrades the subthreshold characteristics. Therefore, a good design should minimize the number of confined quantum well (QW) states at the heterointerface so as not to degrade the subthreshold characteristics while maintaining the lattice mismatch induced polarization to boost the ON-current. We show here that an InAlN QW on an InGaN substrate alloy engineered TFET design is promising to fulfill these requirements. Proper engineering of the alloy mole fractions and the width of the well can eliminate (or at least minimize) the undesired thermalization effects and, at the same time, provide a lattice mismatch to induce a piezoelectric field for boosting the ON-current. We have used a suitable atomistic quantum transport model to simulate these devices. The model accounts for the different mechanisms that are involved, and captures realistic scattering thermalization effects. This model has been benchmarked in our earlier work with experimental measurements of nitride tunneling heterojunction diodes and is used here to optimize the alloy engineered nitride TFET.

Tunneling is a fundamental quantum process with no classical equivalent, which can compete with Coulomb interactions to give rise to complex phenomena. Phosphorus dopants in silicon can be placed with atomic precision to address the different regimes arising from this competition. However, they exploit wavefunctions relying on crystal band symmetries, which tunneling interactions are inherently sensitive to. Here we directly image lattice-aperiodic valley interference between coupled atoms in silicon using scanning tunneling microscopy. Our atomistic analysis unveils the role of envelope anisotropy, valley interference and dopant placement on the Heisenberg spin exchange interaction. We find that the exchange can become immune to valley interference by engineering in-plane dopant placement along specific crystallographic directions. A vacuum-like behaviour is recovered, where the exchange is maximised to the overlap between the donor orbitals, and pair-to-pair variations limited to a factor of less than 10 considering the accuracy in dopant positioning. This robustness remains over a large range of distances, from the strongly Coulomb interacting regime relevant for high-fidelity quantum computation to strongly coupled donor arrays of interest for quantum simulation in silicon., Coupled donor wavefunctions in silicon are spatially resolved to evidence valley interference processes. An atomic-scale understanding of the interplay between interference, envelope anisotropy and crystal symmetries unveils a placement strategy compatible with existing technology where the exchange is insensitive to interference.

Electron spins in Si/SiGe quantum wells suffer from nearly degenerate conduction band valleys, which compete with the spin degree of freedom in the formation of qubits. Despite attempts to enhance the valley energy splitting deterministically, by engineering a sharp interface, valley splitting fluctuations remain a serious problem for qubit uniformity, needed to scale up to large quantum processors. Here, we elucidate and statistically predict the valley splitting by the holistic integration of 3D atomic-level properties, theory and transport. We find that the concentration fluctuations of Si and Ge atoms within the 3D landscape of Si/SiGe interfaces can explain the observed large spread of valley splitting from measurements on many quantum dot devices. Against the prevailing belief, we propose to boost these random alloy composition fluctuations by incorporating Ge atoms in the Si quantum well to statistically enhance valley splitting.

Quantum gates between spin qubits can be implemented leveraging the natural Heisenberg exchange interaction between two electrons in contact with each other. This interaction is controllable by electrically tailoring the overlap between electronic wavefunctions in quantum dot systems, as long as they occupy neighbouring dots. An alternative route is the exploration of superexchange - the coupling between remote spins mediated by a third idle electron that bridges the distance between quantum dots. We experimentally demonstrate direct exchange coupling and provide evidence for second neighbour mediated superexchange in a linear array of three single-electron spin qubits in silicon, inferred from the electron spin resonance frequency spectra. We confirm theoretically through atomistic modeling that the device geometry only allows for sizeable direct exchange coupling for neighbouring dots, while next nearest neighbour coupling cannot stem from the vanishingly small tail of the electronic wavefunction of the remote dots, and is only possible if mediated., 20 pages, 1.4MB, 4 figures

The downscaling of silicon-based structures and proto-devices has now reached the single atom scale, representing an important milestone for the development of a silicon-based quantum computer. One especially notable platform for atomic scale device fabrication is the so-called SiP delta-layer, consisting of an ultra dense and sharp layer of dopants within a semiconductor host. Whilst several alternatives exist, phosphorus dopants in silicon have drawn the most interest, and it is on this platform that many quantum proto-devices have been successfully demonstrated. Motivated by this, both calculations and experiments have been dedicated to understanding the electronic structure of the SiP delta-layer platform. In this work, we use high resolution angle-resolved photoemission spectroscopy (ARPES) to reveal the structure of the electronic states which exist because of the high dopant density of the SiP delta-layer. In contrast to published theoretical work, we resolve three distinct bands, the most occupied of which shows a large anisotropy and significant deviation from simple parabolic behaviour. We investigate the possible origins of this fine structure, and conclude that it is primarily a consequence of the dielectric constant being large (ca. double that of bulk Si). Incorporating this factor into tight binding calculations leads to a major revision of band structure; specifically, the existence of a third band, the separation of the bands, and the departure from purely parabolic behaviour. This new understanding of the bandstructure has important implications for quantum proto-devices which are built on the SiP delta-layer platform., 6 pages, 3 figures

In this work, vertical tunnel field-effect transistors (v-TFETs) based on vertically stacked heretojunctions from 2D transition metal dichalcogenide (TMD) materials are studied by atomistic quantum transport simulations. The switching mechanism of v-TFET is found to be different from previous predictions. As a consequence of this switching mechanism, the extension region, where the materials are not stacked over is found to be critical for turning off the v-TFET. This extension region makes the scaling of v-TFETs challenging. In addition, due to the presence of both positive and negative charges inside the channel, v-TFETs also exhibit negative capacitance. As a result, v-TFETs have good energy-delay products and are one of the promising candidates for low power applications., Comment: didn't reach to co-author agreement

Low-dimensional material systems provide a unique set of properties useful for solid-state devices. The building block of these devices is the p-n junction. In this paper, we present a dramatic difference in the electrostatics of p-n junctions in lower dimensional systems, as against the well understood three dimensional (3-D) systems. Reducing the dimensionality increases the depletion width significantly. We propose a novel method to derive analytic equations in 2-D and 1-D that considers the impact of neutral regions. The analytical results show an excellent match with both the experimental measurements and numerical simulations. The square root dependence of the depletion width on the ratio of dielectric constant and doping in 3-D changes to a linear and exponential dependence for 2-D and 1-D, respectively. This higher sensitivity of 1-D p-n junctions to its control parameters can be used toward new sensors. Utilizing the unconventional electrostatics of these low-dimensional junctions for sensing and switching applications has been discussed and a novel sensor is proposed.

Large-area two-dimensional (2D) heterojunctions are promising building blocks of 2D circuits. Understanding their intriguing electrostatics is pivotal but largely hindered by the lack of direct observations. Here graphene–WS2 heterojunctions are prepared over large areas using a seedless ambient-pressure chemical vapor deposition technique. Kelvin probe force microscopy, photoluminescence spectroscopy, and scanning tunneling microscopy characterize the doping in graphene–WS2 heterojunctions as-grown on sapphire and transferred to SiO2 with and without thermal annealing. Both p–n and n–n junctions are observed, and a flat-band condition (zero Schottky barrier height) is found for lightly n-doped WS2, promising low-resistance ohmic contacts. This indicates a more favorable band alignment for graphene–WS2 than has been predicted, likely explaining the low barriers observed in transport experiments on similar heterojunctions. Electrostatic modeling demonstrates that the large depletion width of the graphene–W...

In this paper, electrostatically configurable 2D tungsten diselenide (WSe

We demonstrate operation of a small Fabry-Perot interferometer in which highly coherent Aharonov-Bohm oscillations are observed in the integer and fractional quantum Hall regimes. Using a novel heterostructure design, Coulomb effects are drastically suppressed. Coherency of edge mode interference is characterized by the energy scale for thermal damping, ${T_0=206}mK$ at $\nu=1$. Selective backscattering of edge modes originating in the ${N=0,1,2}$ Landau levels allows for independent determination of inner and outer edge mode velocities. Clear Aharonov-Bohm oscillations are observed at fractional filling factors $\nu=2/3$ and $\nu=1/3$. Our device architecture provides a platform for measurement of anyonic braiding statistics., Comment: 18 pages, 11 figures. A revised version of this manuscript and supplementary material will appear in Nature Physics

We study the interplay of electron and photon spin in non-reciprocal materials. Traditionally, the primary mechanism to design non-reciprocal photonic devices has been magnetic fields in conjunction with magnetic oxides, such as iron garnets. In this work, we present an alternative paradigm that allows tunability and reconfigurability of the non-reciprocity through spintronic approaches. The proposed design uses the high-spin-orbit coupling of a narrow-band gap semiconductor (InSb) with ferromagnetic dopants. A combination of the intrinsic and a gate-applied electric field gives rise to a strong external Rashba spin-orbit coupling (RSOC) in a magnetically doped InSb film. The RSOC which is gate alterable is shown to adjust the magnetic permeability tensor via the electron g-factor of the medium. We use electronic band structure calculations (k$\cdot$p theory) to show the gate-adjustable RSOC manifest itself in the non-reciprocal coefficient of photon fields via shifts in the Kerr and Faraday rotations. In addition, we show that photon spin properties of dipolar emitters placed in the vicinity of a non-reciprocal electromagnetic environment is distinct from reciprocal counterparts. The Purcell factor (F$_{p}$) of a spin-polarized emitter (right-handed circular dipole) is significantly enhanced due to a larger g-factor while a left-handed dipole remains essentially unaffected. Our work can lead to electron spin controlled reconfigurable non-reciprocal photonic devices., Comment: 10 pages, 7 figures

Self-assembled quantum dots (QDs) are highly strained heterostructures. the lattice strain significantly modifies the electronic and optical properties of these devices. A universal behavior is observed in atomistic strain simulations (in terms of both strain magnitude and profile) of QDs with different shapes and materials. In this paper, this universal behavior is investigated by atomistic as well as analytic continuum models. Atomistic strain simulations are very accurate but computationally expensive. On the other hand, analytic continuum solutions are based on assumptions that significantly reduce the accuracy of the strain calculations, but are very fast. Both techniques indicate that the strain depends on the aspect ratio (AR) of the QDs, and not on the individual dimensions. Thus simple closed form equations are introduced which directly provide the atomistic strain values inside the QD as a function of the AR and the material parameters. Moreover, the conduction and valence band edges $E_{C/V}$ and their effective masses $m^*_{C/V}$ of the QDs are dictated by the strain and AR consequently. The universal dependence of atomistic strain on the AR is useful in many ways; Not only does it reduce the computational cost of atomistic simulations significantly, but it also provides information about the optical transitions of QDs given the knowledge of $E_{C/V}$ and $m^*_{C/V}$ from AR. Finally, these expressions are used to calculate optical transition wavelengths in InAs/GaAs QDs and the results agree well with experimental measurements and atomistic simulations.

The main promise of tunnel FETs (TFETs) is to enable supply voltage ($V_{DD}$) scaling in conjunction with dimension scaling of transistors to reduce power consumption. However, reducing $V_{DD}$ and channel length ($L_{ch}$) typically deteriorates the ON- and OFF-state performance of TFETs, respectively. Accordingly, there is not yet any report of a high perfor]mance TFET with both low V$_{DD}$ ($\sim$0.2V) and small $L_{ch}$ ($\sim$6nm). In this work, it is shown that scaling TFETs in general requires scaling down the bandgap $E_g$ and scaling up the effective mass $m^*$ for high performance. Quantitatively, a channel material with an optimized bandgap ($E_g\sim1.2qV_{DD} [eV]$) and an engineered effective mass ($m*^{-1}\sim40 V_{DD}^{2.5} [m_0^{-1}]$) makes both $V_{DD}$ and $L_{ch}$ scaling feasible with the scaling rule of $L_{ch}/V_{DD}=30~nm/V$ for $L_{ch}$ from 15nm to 6nm and corresponding $V_{DD}$ from 0.5V to 0.2V.

In this work, the performance of Tunnel Field-Effect Transistors (TFETs) based on two-dimensional Transition Metal Dichalcogenide (TMD) materials is investigated by atomistic quantum transport simulations. One of the major challenges of TFETs is their low ON-currents. 2D material based TFETs can have tight gate control and high electric fields at the tunnel junction, and can in principle generate high ON-currents along with a sub-threshold swing smaller than 60 mV/dec. Our simulations reveal that high performance TMD TFETs, not only require good gate control, but also rely on the choice of the right channel material with optimum band gap, effective mass and source/drain doping level. Unlike previous works, a full band atomistic tight binding method is used self-consistently with 3D Poisson equation to simulate ballistic quantum transport in these devices. The effect of the choice of TMD material on the performance of the device and its transfer characteristics are discussed. Moreover, the criteria for high ON-currents are explained with a simple analytic model, showing the related fundamental factors. Finally, the subthreshold swing and energy-delay of these TFETs are compared with conventional CMOS devices., 7 pages, 8 figures. The revised version is uploaded

Exchange coupling is a key ingredient for spin-based quantum technologies since it can be used to entangle spin qubits and create logical spin qubits. However, the influence of the electronic valley degree of freedom in silicon on exchange interactions is presently the subject of important open questions. Here we investigate the influence of valleys on exchange in a coupled donor/quantum dot system, a basic building block of recently proposed schemes for robust quantum information processing. Using a scanning tunneling microscope tip to position the quantum dot with sub-nm precision, we find a near monotonic exchange characteristic where lattice-aperiodic modulations associated with valley degrees of freedom comprise less than 2~\% of exchange. From this we conclude that intravalley tunneling processes that preserve the donor's $\pm x$ and $\pm y$ valley index are filtered out of the interaction with the $\pm z$ valley quantum dot, and that the $\pm x$ and $\pm y$ intervalley processes where the electron valley index changes are weak. Complemented by tight-binding calculations of exchange versus donor depth, the demonstrated electrostatic tunability of donor/QD exchange can be used to compensate the remaining intravalley $\pm z$ oscillations to realise uniform interactions in an array of highly coherent donor spins., Comment: 6 pages, 4 figures, 6 pages Supplemental Material

Built-in hyperfine couplings of donor qubits engineered by precision placement promote addressable electron spin resonance., Phosphorus donor impurities in silicon are a promising candidate for solid-state quantum computing due to their exceptionally long coherence times and high fidelities. However, individual addressability of exchange coupled donors with separations ~15 nm is challenging. We show that by using atomic precision lithography, we can place a single P donor next to a 2P molecule 16 ± 1 nm apart and use their distinctive hyperfine coupling strengths to address qubits at vastly different resonance frequencies. In particular, the single donor yields two hyperfine peaks separated by 97 ± 2.5 MHz, in contrast to the donor molecule that exhibits three peaks separated by 262 ± 10 MHz. Atomistic tight-binding simulations confirm the large hyperfine interaction strength in the 2P molecule with an interdonor separation of ~0.7 nm, consistent with lithographic scanning tunneling microscopy images of the 2P site during device fabrication. We discuss the viability of using donor molecules for built-in addressability of electron spin qubits in silicon.

We identify the presence of monoatomic steps at the Si/SiGe or Si/SiO$_2$ interface as a dominant source of variations in the dephasing time of Si quantum dot (QD) spin qubits. First, using atomistc tight-binding calculations we show that the g-factors and their Stark shifts undergo variations due to these steps. We compare our theoretical predictions with experiments on QDs at a Si/SiO$_2$ interface, in which we observe significant differences in Stark shifts between QDs in two different samples. We also experimentally observe variations in the $g$-factors of one-electron and three-electron spin qubits realized in three neighboring QDs on the same sample, at a level consistent with our calculations. The dephasing times of these qubits also vary, most likely due to their varying sensitivity to charge noise, resulting from different interface conditions. More importantly, from our calculations we show that by employing the anisotropic nature of the spin-orbit interaction (SOI) in a Si QD, we can minimize and control these variations. Ultimately, we predict that the dephasing times of the Si QD spin qubits will be anisotropic and can be improved by at least an order of magnitude, by aligning the external DC magnetic field towards specific crystal directions., 5 pages, 3 figures, Supplemental Material (3 pages, 2 figures)

The 2-D material-based TFETs are among the most promising candidates for low-power electronics applications since they offer ultimate gate control and high-current drives that are achievable through small tunneling distances ( $\Lambda $ ) during the device operation. The ideal device is characterized by a minimized $\Lambda $ . However, devices with the thinnest possible body do not necessarily provide the best performance. For example, reducing the channel thickness ( ${T}_{\text {ch}}$ ) increases the depletion width in the source, which can be a significant part of the total $\Lambda $ . Hence, it is important to determine the optimum ${T}_{\text {ch}}$ for each channel material individually. In this paper, we study the optimum ${T}_{\text {ch}}$ for three channel materials: WSe2, black phosphorus, and InAs using full-band self-consistent quantum transport simulations. To identify the ideal ${T}_{\text {ch}}$ for each material at a specific doping density, a new analytic model is proposed and benchmarked against the numerical simulations.

Spin–orbit coupling (SOC) is fundamental to a wide range of phenomena in condensed matter, spanning from a renormalisation of the free-electron g-factor, to the formation of topological insulators, and Majorana Fermions. SOC has also profound implications in spin-based quantum information, where it is known to limit spin lifetimes (T1) in the inversion asymmetric semiconductors such as GaAs. However, for electrons in silicon—and in particular those bound to phosphorus donor qubits—SOC is usually regarded weak, allowing for spin lifetimes of minutes in the bulk. Surprisingly, however, in a nanoelectronic device donor spin lifetimes have only reached values of seconds. Here, we reconcile this difference by demonstrating that electric field induced SOC can dominate spin relaxation of donor-bound electrons. Eliminating this lifetime-limiting effect by careful alignment of an external vector magnetic field in an atomically engineered device, allows us to reach the bulk-limit of spin-relaxation times. Given the unexpected strength of SOC in the technologically relevant silicon platform, we anticipate that our results will stimulate future theoretical and experimental investigation of phenomena that rely on strong magnetoelectric coupling of atomically confined spins. The lifetime of electron spins bound to phosphorous donors in nanoelectronic silicon devices can be restored to bulk values by suppressing spin–orbit coupling. An international collaboration led by Michelle Simmons of the University of New South Wales, Australia, have measured the lifetimes of a donor-bound spin within a silicon nanoelectronic device, and found it to be of the order of seconds—substantially shorter than in bulk, where the lifetime is on the order of minutes. This difference was found as due to a spin–orbit-induced magnetoelectronic coupling, which impacts spin lifetime and coherence. By countering this effect through a carefully aligned external magnetic field, the researchers could restore the lifetime of the spins in the device to bulk values, which will be helpful in improving performances of quantum devices.

Artificial semiconductors with manufactured band structures have opened up many new applications in the field of optoelectronics. The emerging two-dimensional (2D) semiconductor materials, transition metal dichalcogenides (TMDs), cover a large range of bandgaps and have shown potential in high performance device applications. Interestingly, the ultrathin body and anisotropic material properties of the layered TMDs allow a wide range modification of their band structures by electric field, which is obviously desirable for many nanoelectronic and nanophotonic applications. Here, we demonstrate a continuous bandgap tuning in bilayer MoS2 using a dual-gated field-effect transistor (FET) and photoluminescence (PL) spectroscopy. Density functional theory (DFT) is employed to calculate the field dependent band structures, attributing the widely tunable bandgap to an interlayer direct bandgap transition. This unique electric field controlled spontaneous bandgap modulation approaching the limit of semiconductor-to...

The concept and simulated device characteristics of tunneling field-effect transistors (TFETs) based on III-nitride heterojunctions are presented for the first time. Through polarization engineering, interband tunneling can become significant in III-nitride heterojunctions, leading to the potential for a viable TFET technology. Two prototype device designs, inline and sidewall-gated TFETs, are discussed. Polarization-assisted p-type doping is used in the source region to mitigate the effect of the deep Mg acceptor level in p-type GaN. Simulations indicate that TFETs based on III-nitride heterojunctions can be expected to achieve ON/ OFF ratios of $10^{6}$ or more, with switching slopes well below 60 mV/decade, ON-current densities approaching 100 $\mu \text{A}/\mu \text{m}$ , and energy delay products as low as 67 aJ-ps/ $\mu \text{m}$ .

The effects of strain and confinement on the energy levels and emission spectra of dome-shaped, Ge-core-Si-shell nanocrystals (NCs) with diameters ranging from 5 to 45 nm are investigated with atomistic models. For NCs with base diameters ≥15 nm, the strain-induced increase in the energy gap is ∼100 meV. The increase in the energy gap is primarily the result of the downward shift in the occupied states confined in the Ge core. The fundamental energy gap varies from 960 meV to 550 meV as the NC diameter increases from 5 nm to 45 nm. Confinement and strain break the degeneracy of the lowest excited state and split it into two states separated by a few meV. For the smaller NCs, one of these states can be localized in the Si core and the other state can be in the Si cap. For diameters ≥20 nm, both of these states are localized in the Si cap. The electronic states are calculated using an atomistic sp(3)d(5)s* tight-binding model including spin-orbit coupling, and geometry relaxation is performed using a valence force field model.

In this work, we develop and employ a multiscale-multiphysics simulator (based on coupled VFF molecular mechanics, 10-band sp3s∗-spin tight-binding formalism, many-body full configuration interaction, and a TCAD transport module) to study and compare the performance of realistically-sized multiple-quantum-well wurtzite InGaN LEDs in polar (c-plane) and nonpolar (a-plane) crystallographic directions. The a-plane device exhibited smaller yet non-vanishing internal fields and higher optical transition rate as compared to the c-plane counterpart.

We demonstrate the single-shot spin read-out of single donors and few-donor clusters, positioned with atomic precision by scanning tunneling microscopy (STM) in atomically engineered silicon devices [1-3]. In donor clusters, we measure spin lifetimes of up to half a minute, recorded at a read-out fidelity of up to 99.8% [2]. Importantly, measuring spin relaxations rates of electrons bound to a single P donor in orientation-dependent electric and magnetic fields, we identify a previously unreported spin relaxation pathway for donor-based qubits in silicon [1].

Large-area two-dimensional (2D) heterojunctions are promising building blocks of 2D circuits. Understanding their intriguing electrostatics is pivotal but largely hindered by the lack of direct observations. Here graphene-WS