Showing papers in "Applied Physics Letters in 2020"

Oxygen vacancies: The (in)visible friend of oxide electronics

Abstract: Oxygen vacancies play crucial roles in determining the physical properties of metal oxides, representing important building blocks in many scientific and technological fields due to their unique chemical, physical, and electronic properties. However, oxygen vacancies are often invisible because of their dilute concentrations. Therefore, characterizing and quantifying their presence is of utmost importance for understanding and realizing functional metal oxide devices. This, however, is oftentimes a non-trivial task. In this Perspective paper, we discuss the relevant regimes of concentrations and associated phenomena arising from oxygen vacancies. We then focus on experimental techniques available for observing oxygen vacancies at widely different levels of concentrations. Finally, we discuss current challenges and opportunities for utilizing oxygen vacancies in metal oxides.

Liquid crystal programmable metasurface for terahertz beam steering

Abstract: The coding metasurface integrated with tunable materials offers an attractive alternative to manipulate the THz beam dynamically. In this work, we demonstrate a THz programmable metasurface based on liquid crystal. The phase profile on the metasurface could be dynamically manipulated by switching the “0” and “1” states of each element. The programmable metasurface could deflect the THz beam using the designed coding sequence, and a maximum deflection angle of 32° has been achieved. The presented design opens a route of beamforming for THz communication.

High performance CsPbBr3 quantum dots photodetectors by using zinc oxide nanorods arrays as an electron-transport layer

Abstract: The electron transport layer (ETL) in perovskite photodetectors is playing a vital role in highly efficient electron extraction. Herein, this work reports a perovskite photodetector based on hydrothermal-fabricated ZnO nanorods (NRs) as the ETL and hot-injection-fabricated CsPbBr3 quantum dot (QD) as the photoabsorber. The crystalline structure, morphologies, and photoluminescence (PL) of the materials and the physics mechanism of highly efficient electron extraction in the devices are characterized and analyzed. The PL and time-resolved PL confirm the reduced recombination and enhanced electron transport to the indium tin oxide anode. The photodetectors based on ZnO NRs/CsPbBr3 QDs exhibit enormous enhancement in the response parameters such as a rise time of 12 ms, a decay time of 38 ms, and an on/off ratio of 3000, compared with the photodetectors based on ZnO films/CsPbBr3 QDs. These results indicate that the fabricated ZnO NRs/CsPbBr3 QDs heterojunction has a wide prospect of future applications in photodetectors.

A 1.86-kV double-layered NiO/β-Ga2O3 vertical p–n heterojunction diode

Abstract: In this Letter, high-performance vertical NiO/β-Ga2O3 p–n heterojunction diodes without any electric field managements were reported. The devices show a low leakage current density and a high rectification ratio over 1010 (at ±3 V) even operated at temperature of 400 K, indicating their excellent thermal stability and operation capability at high temperature. Given a type-II band alignment of NiO/β-Ga2O3, carrier transport is dominated by the interface recombination at forward bias, while the defect-mediated variable range hopping conduction is identified upon strong reverse electric field. By using the double-layer design of NiO with a reduced hole concentration of 5.1 × 1017 cm−3, the diode demonstrates an improved breakdown voltage (Vb) of 1.86 kV and a specific on-resistance (Ron,sp) of 10.6 mΩ cm2, whose power figure of merit (Vb2/Ron,sp) has reached 0.33 GW/cm2. The high breakdown voltage and low leakage current are outperforming other reported Ga2O3 based p–n heterojunctions and Schottky barrier diodes without field plate and edge termination structures. TCAD simulation indicates that the improved Vb is mainly attributed to the suppression of electric field crowding due to the decreased hole concentration in NiO. Such bipolar heterojunction is expected to be an alternative to increase the breakdown characteristics of β-Ga2O3 power devices.

Development of microLED

Abstract: This perspective provides an overview of early developments, current status, and remaining challenges of microLED (μLED) technology, which was first reported in Applied Physics Letters in 2000 [S. X. Jin, J. Li, J. Z. Li, J. Y. Lin and H. X. Jiang, "GaN Microdisk Light Emitting Diodes," Appl. Phys. Lett. 76, 631 (2000)]. Today, microLED is recognized as the ultimate display technology and is one of the fastest-growing technologies in the world as technology giants utilize it on a wide range of products from large flat panel displays and televisions, wearable displays, and virtual reality displays to light sources for the neural interface and optogenetics. It is anticipated that the collective R&D efforts worldwide will bring microLED products not only to the mass consumer electronic markets but also to serve the society on the broadest scale by encompassing sectors in medical/health, energy, transportation, communications, and entertainment.

Comparison of size-dependent characteristics of blue and green InGaN microLEDs down to 1 μm in diameter

Abstract: There is growing interest in microLED devices with lateral dimensions between 1 and 10 μm. However, reductions in external quantum efficiency (EQE) due to increased nonradiative recombination at the surface become an issue at these sizes. Previous attempts to study size-dependent EQE trends have been limited to dimensions above 5 μm, partly due to fabrication challenges. Here, we present size-dependent EQE data for InGaN microLEDs down to 1 μm in diameter fabricated using a process that only utilizes standard semiconductor processing techniques (i.e., lithography and etching). Furthermore, differences in EQE trends for blue and green InGaN microLEDs are compared. Green wavelength devices prove to be less susceptible to reductions in efficiency with the decreasing size; consequently, green devices attain higher EQEs than blue devices below 10 μm despite lower internal quantum efficiencies in the bulk material. This is explained by smaller surface recombination velocities with the increasing indium content due to enhanced carrier localization.

Developing silicon carbide for quantum spintronics

Abstract: In current long-distance communications, classical information carried by large numbers of particles is intrinsically robust to some transmission losses but can, therefore, be eavesdropped without notice. On the other hand, quantum communications can provide provable privacy and could make use of entanglement swapping via quantum repeaters to mitigate transmission losses. To this end, considerable effort has been spent over the last few decades toward developing quantum repeaters that combine long-lived quantum memories with a source of indistinguishable single photons. Multiple candidate optical spin qubits in the solid state, including quantum dots, rare-earth ions, and color centers in diamond and silicon carbide (SiC), have been developed. In this perspective, we give a brief overview on recent advances in developing optically active spin qubits in SiC and discuss challenges in applications for quantum repeaters and possible solutions. In view of the development of different material platforms, the perspective of SiC spin qubits in scalable quantum networks is discussed.

Exploiting the advantages of the centrifugal softening effect in rotational impact energy harvesting

Abstract: This Letter presents a rotational impact energy harvester by utilizing the centrifugal softening effect of an inverted driving beam in improving the energy harvesting performance of two piezoelectric beams at low rotational frequencies. By our proposed structure, the static divergence of the inverted driving beam in the deflected mode can not only be avoided but also be utilized. Numerical and experimental results show that the centrifugal softening effect can amplify the relative motion between the driving and generating beams and increase the impact force, which in turn improves the output power significantly. The maximum output power of the harvester is increased by 212.5%, 258.7%, and 682.8% for the impact gaps of 1.07 mm, 1.43 mm, and 2.14 mm, respectively. Moreover, the inverted driving beam can be prevented from continuously deflecting by introducing large impact stiffness at the contact instant.

Quantum dot arrays in silicon and germanium

Abstract: Electrons and holes confined in quantum dots define excellent building blocks for quantum emergence, simulation, and computation. Silicon and germanium are compatible with standard semiconductor manufacturing and contain stable isotopes with zero nuclear spin, thereby serving as excellent hosts for spins with long quantum coherence. Here, we demonstrate quantum dot arrays in a silicon metal-oxide-semiconductor (SiMOS), strained silicon (Si/SiGe), and strained germanium (Ge/SiGe). We fabricate using a multi-layer technique to achieve tightly confined quantum dots and compare integration processes. While SiMOS can benefit from a larger temperature budget and Ge/SiGe can make an Ohmic contact to metals, the overlapping gate structure to define the quantum dots can be based on a nearly identical integration. We realize charge sensing in each platform, for the first time in Ge/SiGe, and demonstrate fully functional linear and two-dimensional arrays where all quantum dots can be depleted to the last charge state. In Si/SiGe, we tune a quintuple quantum dot using the N + 1 method to simultaneously reach the few electron regime for each quantum dot. We compare capacitive crosstalk and find it to be the smallest in SiMOS, relevant for the tuning of quantum dot arrays. We put these results into perspective for quantum technology and identify industrial qubits, hybrid technology, automated tuning, and two-dimensional qubit arrays as four key trajectories that, when combined, enable fault-tolerant quantum computation.

Interfacial charge transfer exciton enhanced by plasmon in 2D in-plane lateral and van der Waals heterostructures

Abstract: The multi-scale computational method of combining the first-principles calculation and finite element electromagnetic simulations is used to study the plasmon-enhanced interlayer charge transfer (CT) exciton of 2D lateral and van der Waals MoS2/WS2 heterostructures with the 2H phase. The weak interlayer CT excitons are observed in the 2H lateral and van der Waals MoS2/WS2 heterostructures. Theoretical results reveal the physical principle of plexcitons resulting from the strong coupling between plasmons and interlayer CT excitons. The weak CT excitons can be strongly enhanced by a metal plasmon, which provides a way to observe the weak CT excitons. Our results can promote a deeper understanding of the plexciton resulting from strong coupling interaction between the plasmon and the exciton of lateral and van der Waals heterostructures.

Systematic investigation of the growth kinetics of β-Ga2O3 epilayer by plasma enhanced chemical vapor deposition

Abstract: β-Ga2O3 has attracted much attention due to its ultrawide-bandgap (∼4.9 eV) with a high breakdown field (8 MV/cm) and good thermal/chemical stability. In order for β-Ga2O3 to be used in electronic and optoelectronic devices, epitaxial growth technology of thin films should be given priority. However, challenges are associated with the trade-off growth rate with crystallization and surface roughness in conventional epitaxy. Herein, plasma enhanced chemical vapor deposition was used to grow the β-Ga2O3 epilayer, and the growth kinetics process has been systematically investigated. A high growth rate of ∼0.58 μm/h and a single 2 ¯ 01 plane orientation with a full width at half maximum value of 0.86° were obtained when grown on the c-plane sapphire substrate at the growth temperature of 820 °C. Then, a proposed model for the mechanism of nucleation and growth of β-Ga2O3 epitaxial films is established to understand the precursor transport and gas phase reaction process. This work provides a cheap, green, and efficient epitaxial growth method, which is indispensable for device applications of β-Ga2O3.

Quantum neuromorphic computing

Abstract: Quantum neuromorphic computing physically implements neural networks in brain-inspired quantum hardware to speed up their computation. In this perspective article, we show that this emerging paradigm could make the best use of the existing and near future intermediate size quantum computers. Some approaches are based on parametrized quantum circuits and use neural network-inspired algorithms to train them. Other approaches, closer to classical neuromorphic computing, take advantage of the physical properties of quantum oscillator assemblies to mimic neurons and synapses to compute. We discuss the different implementations of quantum neuromorphic networks with digital and analog circuits, highlight their respective advantages, and review exciting recent experimental results.

Revealing the importance of light extraction efficiency in InGaN/GaN microLEDs via chemical treatment and dielectric passivation

Abstract: Chemical etching and Al2O3 dielectric passivation were used to minimize nonradiative sidewall defects in InGaN/GaN microLEDs (mesa diameter = 2–100 μm), resulting in an increase in external quantum efficiency (EQE) as the LED size was decreased Peak EQEs increased from 8%–10% to 12%–135% for mesa diameters from 100 μm to 2 μm, respectively, and no measurable leakage currents were seen in current density–voltage (J–V) characteristics The position and shape of EQE curves for all devices were essentially identical, indicating size-independent ABC model (Shockley–Read–Hall, radiative, and Auger recombination) coefficients-behavior that is not typical of microLEDs as the size decreases These trends can be explained by enhancement in light extraction efficiency (LEE), which is only observable when sidewall defects are minimized, for the smallest LED sizes Detailed ray-tracing simulations substantiate the LEE enhancements

Ultra-high sensitive trace gas detection based on light-induced thermoelastic spectroscopy and a custom quartz tuning fork

Abstract: A highly sensitive trace gas sensor based on light-induced thermoelastic spectroscopy (LITES) and a custom quartz tuning fork (QTF) is reported. The QTF has a T-shaped prong geometry and grooves carved on the prongs' surface, allowing a reduction of both the resonance frequency and the electrical resistance but retaining a high resonance quality factor. The base of the QTF prongs is the area maximizing the light-induced thermoelastic effect. The front surface of this area was left uncoated to allow laser transmission through the quartz, while on the back side of the QTF, a gold film was coated to back-reflect the laser beam and further enhance the light absorption inside the crystal. Acetylene (C2H2) was chosen as the target gas to test and validate the LITES sensor. We demonstrated that the sensor response scales linearly with the laser power incident on the prong base, and the optimum signal to noise ratio was obtained at an optical power of 4 mW. A minimum detection limit of ∼325 ppb was achieved at an integration time of 1 s, corresponding to a normalized noise equivalent absorption coefficient of 9.16 × 10−10 cm−1W/√Hz, nearly one order of magnitude better with respect to the value obtained with a standard 32.768 kHz QTF-based LITES sensor under the same experimental conditions.

633-nm InGaN-based red LEDs grown on thick underlying GaN layers with reduced in-plane residual stress

Abstract: This work investigates the influence of residual stress on the performance of InGaN-based red light-emitting diodes (LEDs) by changing the thickness of the underlying n-GaN layers. The residual in-plane stress in the LED structure depends on the thickness of the underlying layer. Decreased residual in-plane stress resulting from the increased thickness of the underlying n-GaN layers improves the crystalline quality of the InGaN active region by allowing for a higher growth temperature. The electroluminescence intensity of the InGaN-based red LEDs is increased by a factor of 1.3 when the thickness of the underlying n-GaN layer is increased from 2 to 8 μm. Using 8-μm-thick underlying n-GaN layers, 633-nm-wavelength red LEDs are realized with a light-output power of 0.64 mW and an external quantum efficiency of 1.6% at 20 mA. The improved external quantum efficiency of the LEDs can be attributed to the lower residual in-plane stress in the underlying GaN layers.

Recent developments, challenges, and pathways to stable dropwise condensation: A perspective

Abstract: Dropwise condensation (DWC) on non-wetting surfaces has remarkable potential to enhance heat transfer performance compared to filmwise condensation on wetting substrates. In this article, we discuss important recent developments and challenges in the field of DWC, including durability of DWC-promoting coatings, DWC of low surface tension fluids, physical mechanisms governing DWC, unconventional methods to achieve DWC, and promising metrology techniques for DWC. We end the article by providing a road map detailing where we believe the community should direct both fundamental and applied efforts in order to solve the identified century-old challenges that limit DWC implementation.

Labyrinthine acoustic metastructures enabling broadband sound absorption and ventilation

Abstract: There is growing interest in the development of path coiling-based labyrinthine acoustic metamaterials for realizing extraordinary acoustical properties such as low-to-mid frequency sound absorption. We present a subwavelength labyrinthine acoustic metastructure ( ≤3 cm) exhibiting a superior sound absorption with a high bandwidth (more than one octave in the range of 400–1400 Hz). The metastructure is orchestrated of multiple labyrinthine unit cells of different configurations in a hexagonal array, and broadband absorption has been achieved by the dissipation of incident propagating sound waves inside the labyrinthine zigzag channels. Furthermore, the unique design of the metastructure allows for simultaneous air circulation for facilitating natural ventilation and sound absorption. The proposed unique designs may find potential applications in architectural acoustics and noise shielding where simultaneous natural ventilation and noise mitigation are required.

A Predictive Model of the Temperature-Dependent Inactivation of Coronaviruses

Abstract: The COVID-19 pandemic has stressed healthcare systems and supply lines, forcing medical doctors to risk infection by decontaminating and reusing single-use personal protective equipment. The uncertain future of the pandemic is compounded by limited data on the ability of the responsible virus, SARS-CoV-2, to survive across various climates, preventing epidemiologists from accurately modeling its spread. However, a detailed thermodynamic analysis of experimental data on the inactivation of SARS-CoV-2 and related coronaviruses can enable a fundamental understanding of their thermal degradation that will help model the COVID-19 pandemic and mitigate future outbreaks. This work introduces a thermodynamic model that synthesizes existing data into an analytical framework built on first principles, including the rate law for a first-order reaction and the Arrhenius equation, to accurately predict the temperature-dependent inactivation of coronaviruses. The model provides much-needed thermal decontamination guidelines for personal protective equipment, including masks. For example, at 70 °C, a 3-log (99.9%) reduction in virus concentration can be achieved, on average, in 3 min (under the same conditions, a more conservative decontamination time of 39 min represents the upper limit of a 95% interval) and can be performed in most home ovens without reducing the efficacy of typical N95 masks as shown in recent experimental reports. This model will also allow for epidemiologists to incorporate the lifetime of SARS-CoV-2 as a continuous function of environmental temperature into models forecasting the spread of the pandemic across different climates and seasons.

MOCVD growth of high purity Ga2O3 epitaxial films using trimethylgallium precursor

Abstract: We report on the growth of β-Ga2O3 thin films using trimethylgallium (TMGa) as a source for gallium and pure O2 for oxidation. The growth rate of the films was found to linearly increase with the increase in the molar flow rate of TMGa and reach as high as ∼6 μm/h at a flow rate of 580 μmol/min. High purity, lightly Si-doped homoepitaxial β-Ga2O3 films with a good surface morphology, a record low temperature electron mobility exceeding 23 000 cm2/V s at 32 K, and an acceptor concentration of 2 × 1013 cm−3 were realized, showing an excellent purity film. Films with room temperature (RT) electron mobilities ranging from 71 cm2/V s to 138 cm2/V s with the corresponding free carrier densities between ∼1.1 × 1019 cm−3 and ∼1.5 × 1016 were demonstrated. For layers with the doping concentration in the range of high-1017 and low-1018 cm−3, the RT electron mobility values were consistently more than 100 cm2/V s, suggesting that TMGa is suitable to grow channel layers for lateral devices, such as field effect transistors. The results demonstrate excellent purity of the films produced and confirm the suitability of the TMGa precursor for the growth of device quality β-Ga2O3 films at a fast growth rate, meeting the demands for commercializing Ga2O3-based high voltage power devices by metalorganic chemical vapor deposition.

Experimental demonstration of externally driven millimeter-wave particle accelerator structure

Abstract: We report the experimental demonstration of a mm-wave electron accelerating structure powered by a high-power rf source. We demonstrate reliable coupling of an unprecedented rf power—up to 575 kW into the mm-wave accelerator structure using a quasi-optical setup. This standing wave accelerating structure consists of a single-cell copper cavity and a Gaussian to TM01 mode converter. The accelerator structure is powered by 110 GHz, 10-ns long rf pulses. These pulses are chopped from 3 ms pulses from a gyrotron oscillator using a laser-driven silicon switch. We show an unprecedented high gradient up to 230 MV/m that corresponds to a peak surface electric field of more than 520 MV/m. We have achieved these results after conditioning the cavity with more than 105 pulses. We also report preliminary measurements of rf breakdown rates, which are important for understanding rf breakdown physics in the millimeter-wave regime. These results open up many frontiers for applications not only limited to the next generation particle accelerators but also x-ray generation, probing material dynamics, and nonlinear light-matter interactions at mm-wave frequency.

Near-ideal reverse leakage current and practical maximum electric field in β-Ga2O3 Schottky barrier diodes

Abstract: We investigate the intrinsic reverse leakage mechanisms in Ni-based Schottky barrier diodes (SBDs) fabricated on a ( 2 ¯01) single crystal β-Ga2O3 substrate, where a uniform bulk reverse leakage current has been designed and confirmed. The temperature-dependent reverse leakage characteristics are analyzed by a numerical reverse leakage model, which includes both the image-force lowering and doping effects. We found that the reverse leakage current is near-ideal and dominated by Schottky barrier tunneling throughout the entire range of the surface electric field from 0.8 MV/cm to 3.4 MV/cm. The extracted barrier height from the reverse leakage model is consistent with the values extracted from the forward current–voltage and capacitance–voltage measurements. The practical maximum electric field, defined by the maximum allowable reverse leakage current levels, is calculated as a function of the barrier height. These results suggest that it is possible to approach the intrinsic breakdown electric field in β-Ga2O3 SBDs, as long as a sufficiently high barrier height (∼2.2 to 3 eV) is employed.

Electrically tunable high Curie temperature two-dimensional ferromagnetism in van der Waals layered crystals

Abstract: Identifying intrinsic low-dimensional ferromagnets with high magnetic transition temperature and electrically tunable magnetism is crucial for the development of miniaturized spintronics and magnetoelectrics. Recently, long-range 2D ferromagnetism was observed in van der Waals crystals CrI3 and Cr2Ge2Te6, however, their Curie temperature is significantly lowered when reducing down to monolayer/few layers. Herein, using renormalized spin-wave theory and first-principles electronic structure theory, we present a theoretical study of electrically tunable 2D ferromagnetism in van der Waals layered CrSBr and CrSeBr semiconductors with a high Curie temperature of ∼150 K and a sizable bandgap. The high transition temperature is attributed to the strong anion-mediated superexchange interaction and a sizable spin-wave excitation gap due to large exchange and single-ion anisotropy. Remarkably, hole and electron doping can switch the magnetization easy axis from the in-plane to the out-of-plane direction. These unique characteristics establish monolayer CrSBr and CrSeBr as a promising platform for realizing 2D spintronics and magnetoelectrics such as 2D spin valves and spin field effect transistors.

Spintronics with compensated ferrimagnets

Abstract: Magnetic information storage has been achieved by controlling and sensing the magnetic moment orientation of nanoscale ferromagnets. Recently, there has been concentrated effort to utilize materials with antiferromagnetic coupling as a storage medium to realize devices that switch faster, are more secure against external magnetic fields, and have higher storage density. Within this class of materials are ferrimagnets, whose magnetization can be reduced to zero by tuning parameters such as the chemical composition, temperature, and strain. Compared to conventional antiferromagnets, compensated ferrimagnets not only possess the aforementioned speed and density advantages but also allow the use of convenient electrical reading and writing mechanisms due to the existence of inequivalent magnetic sublattices. Recent research has demonstrated fast spin-torque switching, as well as efficient electrical reading with compensated ferrimagnets. Further material and device research using these zero-moment magnets promises a spintronic platform for fast and energy efficient information storage technology.

Deterministic quantum entanglement between macroscopic ferrite samples

Abstract: We show how macroscopic magnetic samples like yttrium iron garnet samples are excellent candidates for producing deterministic quantum entanglement and, thus, providing a platform for quantum information science. This requires strong coupling with a high quality cavity, which, in turn, provides an effective coupling between the two samples. For modest values of the squeezing of the pump, we obtain significant entanglement between the two garnet samples. This is the principal feature of our scheme. We present a number of tests for entanglement in terms of the experimentally observed quantities and, in this way, unfold a paradigm for producing entanglement. We also generate quantum states of collective magnon variables.

Optimizing the efficiency of a periodically poled LNOI waveguide using in situ monitoring of the ferroelectric domains

Abstract: Lithium niobate on insulator (LNOI) is a unique platform for integrated photonic applications and especially for high-efficiency nonlinear frequency converters because of the strong optical field confinement. In this work, we fabricated a 6-mm-long periodically poled LNOI ridge waveguide with an optimized duty cycle (50:50) using an active domain structure monitoring method. The performance of the single-pass second-harmonic generation and difference-frequency generation in the nanophotonic waveguide was characterized, and the normalized conversion efficiencies were ∼80% of the theoretical values. These high-quality frequency conversion devices can pave the way for the application of LNOI in nonlinear integrated photonics.

Time-domain characterization and correction of on-chip distortion of control pulses in a quantum processor

Abstract: We introduce Cryoscope, a method for sampling on-chip baseband pulses used to dynamically control qubit frequency in a quantum processor. We specifically use Cryoscope to measure the step response of the dedicated flux control lines of two-junction transmon qubits in circuit QED processors with the temporal resolution of the room-temperature arbitrary waveform generator producing the control pulses. As a first application, we iteratively improve this step response using optimized real-time digital filters to counter the linear-dynamical distortion in the control line, as needed for high-fidelity repeatable one- and two-qubit gates based on dynamical control of qubit frequency.

Ultra-thin Hf0.5Zr0.5O2 thin-film-based ferroelectric tunnel junction via stress induced crystallization

Abstract: We report on 4.5-nm-thick Hf0.5Zr0.5O2 (HZO) thin-film-based ferroelectric tunnel junctions (FTJs) with a tungsten (W) bottom electrode. The HZO on the W electrode exhibits stable ferroelectricity with a remanent polarization of 14 μC/cm2, an enhanced tunneling electroresistance of 16, and excellent synaptic properties. We found that a large tensile stress was induced on a HZO thin film, owing to a low thermal expansion coefficient of the W bottom electrode. The low thermal expansion coefficient results in the effective formation of an orthorhombic phase, even in an ultra-thin HZO film. This was verified by a comparative study of the electrical characteristics, grazing-angle incidence x-ray diffraction, and residual stress measurement of the HZO film on various bottom electrodes with different thermal expansion coefficients. In addition, this study demonstrates the suitable functions of the FTJ for electronic synapses, such as analog-like resistance transition under various pulse schemes. The fabricated stress-engineered FTJ exhibits an appropriate conductance ratio, linearly modulated long-term potentiation and depression characteristics, and excellent reliability. These characteristics render FTJs ideal electronic devices for neuromorphic computing systems.

Atomistic defects as single-photon emitters in atomically thin MoS2

Abstract: Precisely positioned and scalable single-photon emitters (SPEs) are highly desirable for applications in quantum technology. This Perspective discusses single-photon-emitting atomistic defects in monolayers of MoS2 that can be generated by focused He-ion irradiation with few nanometers positioning accuracy. We present the optical properties of the emitters and the possibilities to implement them into photonic and optoelectronic devices. We showcase the advantages of the presented emitters with respect to atomistic positioning, scalability, long (microsecond) lifetime, and a homogeneous emission energy within ensembles of the emitters. Moreover, we demonstrate that the emitters are stable in energy on a timescale exceeding several weeks and that temperature cycling narrows the ensembles' emission energy distribution.

A recipe for creating ideal hybrid memristive-CMOS neuromorphic processing systems

Abstract: The development of memristive device technologies has reached a level of maturity to enable the design and fabrication of complex and large-scale hybrid memristive-Complementary Metal-Oxide Semiconductor (CMOS) neural processing systems. These systems offer promising solutions for implementing novel in-memory computing architectures for machine learning and data analysis problems. We argue that they are also ideal building blocks for integration in neuromorphic electronic circuits suitable for ultra-low power brain-inspired sensory processing systems, therefore leading to innovative solutions for always-on edge-computing and Internet-of-Things applications. Here, we present a recipe for creating such systems based on design strategies and computing principles inspired by those used in mammalian brains. We enumerate the specifications and properties of memristive devices required to support always-on learning in neuromorphic computing systems and to minimize their power consumption. Finally, we discuss in what cases such neuromorphic systems can complement conventional processing ones and highlight the importance of exploiting the physics of both the memristive devices and the CMOS circuits interfaced to them.