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We have built a Terahertz Dispersive Fourier Transform Spectrometer \cite{Birch1987} to study frequency properties of superconducting films used for fabrication of THz detectors. The signal reflected from the tested film is measured in time domain, which allows to separate it from the other reflections. The complex conductivity of the film depends on frequency and determines the reflection coefficient. By comparing the film reflection in the superconducting state (temperature is below $T_c$) with the reflection of the normal state, we characterise the film quality at terahertz frequencies. The method was applied to 70 and 200nm thick Nb films on a silicon wafer and to 360nm thick NbTiN films on silicon and quartz wafers. The strong-coupling coefficient, $\alpha$, was found to be 3.52 for Nb, and 3.71-4.02 for the NbTiN films. The experimental results were fitted using extended Mattis-Bardeen theory \cite{Noguchi2012} and show a good agreement., Comment: The following article has been accepted by Applied Physics Letters. After it is published, it will be found at https://aip.scitation.org/journal/apl

International audience; Scaling of planar HfO2-based ferroelectric capacitors is investigated experimentally by varying the capacitor area within 5 orders of magnitude, under the scope of limited thermal budget for crystallization. Both Hf0.5Zr0.5O2 (HZO) and Si-doped HfO2 (HSO) based metal/ferroelectric/metal (MFM) capacitors with 10 nm dielectric film thickness and TiN electrodes are demonstrated to be ferroelectric when integrated in a back-end of line (BEOL) of 130 nm CMOS technology, with a maximum thermal budget below 500°C. When the area of the ferroelectric capacitors is scaled down from 7850 µm² to 0.28 µm², no degradation of the remanent polarization (2•PR > 10 µC/cm² for HSO, > 30 µC/cm² for HZO) or of the switching kinetics (down to 100 ns at 3V) is observed. Significant improvement of the field cycling endurance is demonstrated upon area scaling, consistent with the reduction of the total number of defects when devices are shrunk. The results pave the way to future BEOL demonstrations in 130 nm and more advanced nodes with record endurance similar to perovskite ferroelectrics.

著者人数: 15名, Accepted: 2020-02-11, 資料番号: SA1190184000

Multiple polymorphs coexist in doped HfO2 ferroelectric material, and their relative fraction depends on the dopant concentration. The ferroelectric properties originate only from the polar orthorhombic Pca21 phase, which can be stabilized in a binary mixture of HfO2 and ZrO2 at a low thermal budget. However, this material suffers from limited field cycling endurance. Additional doping with La improves the field cycling endurance by several orders of magnitude. Hence, La doping is of interest to have better operational reliability. The dynamics of phase formation in Hf0.5Zr0.5O2 is well established, but they have not been investigated in the recently reported La:Hf0.5Zr0.5O2 in detail. In this work, a comprehensive analysis of stability dynamics of polymorphs in La:Hf1−xZrxO2 with different La doping concentrations and its implications on ferroelectric properties is reported.

The reliability of Hf0.5Zr0.5O2 (HZO) metal–ferroelectric–semiconductor capacitors grown by plasma-assisted atomic oxygen deposition on Ge substrates is investigated with an emphasis on the influence of crystallization annealing. The capacitors show very weak wake-up and imprint effects, allowing reliable operation in excess of 10 years, which is attributed partly to the clean, oxide-free Ge/HZO bottom interface. The weak temperature dependence and the observed asymmetries between polarization up and down states and between positive and negative coercive voltage shifts lead to the conclusion that imprint is controlled by carrier injection at the top electrode interface. The latter mechanism is associated with trapping at interfacial oxygen-vacancy defects. On the other hand, using ultrafast (millisecond) flash annealing improves the leakage current by at least an order of magnitude and the endurance by a factor of 3 compared to conventional rapid thermal annealing, which makes them suitable for low power nonvolatile memory applications where (ultra)thin HZO is an essential requirement.

Germanium Metal-Ferroelectric-Semiconductor (MFS) capacitors based on ferroelectric Hf1−xZrxO2 (HZO) with clean, oxide free Ge/HZO interfaces emerge as an interesting layer structure for the fabrication of ferroelectric field effect transistor (FeFET) non-volatile memory devices. It is shown that, at low temperature (

Little is known regarding the liquid structure of materials compressed to extreme conditions, and even less is known about liquid structures undergoing rapid compression on nanosecond timescales. Here we report on liquid structure factor and radial distribution function measurements of tin shock compressed to 84(19) GPa. High-quality, femtosecond x-ray diffraction measurements at the Linac Coherent Light Source were used to extract the liquid diffuse scattering signal. From the radial distribution function, we find that the structural evolution of the liquid with increasing pressuremimics the evolution of the solid phase. With increasing pressure we find that the liquid structure evolves from a complex structure, with low coordination number, to a simple liquid structure with a coordination number of ∼ 12.We provide a pathway for future experiments to study liquids at elevated pressures using high-energy lasers to shock compress materials beyond the reach of static diamond anvil cell techniques.

Formation of highly ordered nanostructures on a crystalline silicon surface is highly demanded for novel optoelectronic and nanophotonic designs pushing toward development of inexpensive and high-performing nanostructuring technologies. Here, we demonstrate that laser-induced periodic surface structuring of c-Si protected by a thin Hf over-layer allows one to fabricate extremely uniform high-aspect-ratio gratings with a characteristic periodicity of ≈900–950 and 450 nm. Corresponding ordering originates from interference of incident IR femtosecond laser pulses with surface plasmons as well as doubling of the grating period via interference of counter-propagating plasmons. A high-melting-point Hf over-layer regulates the c-Si ablation in the plasmon-mediated interference maxima and prevents its excessive oxidation upon multi-pulse exposure in ambient environment. Considering unique high-aspect ratio morphology (a depth-to-period ratio of up to 1.24 and a depth-to-width ratio of up to 8) of the reported nanogratings, their outstanding uniformity, and rather fast printing rate of ≈0.2 mm2/s as well as possibility for its further upscaling, we envision high practical applicability of this technology in novel optoelectronic devices, visible and near-IR optics, all-dielectric metasurfaces, and sensors.

Metal-oxide-semiconductor light-emitting devices (MOSLEDs) based on erbium doped Al2O3 nanofilms still suffer from insufficient and unstable electrical injection. Here, Al2O3/Ga2O3:Er nanolaminate films are fabricated by atomic layer deposition on silicon, in which the insertion of atomic Ga2O3 layers greatly improves the tolerance to the electric field and electron injection of the Al2O3:Er MOSLEDs, thus leading to the outstanding electroluminescence (EL) performance. The maximum injection current is raised from 0.21 A/cm2 up to 1.05 A/cm2 with the optical power density reaching 10.23 mW/cm2. Much higher excitation efficiencies are also achieved with an external quantum efficiency of 14.2% and a power efficiency of 0.16%. Moreover, the operation time of the prototype Al2O3/Ga2O3:Er MOSLEDs is enhanced 21 times compared with the devices without Ga2O3. In addition, the Al2O3/Ga2O3:Er nanolaminate devices can realize EL under alternating-current excitation. This work supplies a promising route to improve the EL performance of rare earth doped Al2O3 nanofilms for the applications in optoelectronics.

The structural and electronic properties of two-dimensional gallium nitrides (2D GaNs) on a van der Waals (vdW) epitaxial substrate are investigated using first-principles calculations. We show that the structures and electronic properties of mono- and bilayer GaN are hardly affected when deposited on the vdW substrate comprising a graphene sheet placed on the GaN(0001) bulk surface. A weak attractive interaction is found to work between the 2D GaNs and vdW substrate, which is still sufficient to maintain the 2D GaNs on the substrate and could also be exploited to control their stability. The present findings demonstrate that the vdW substrate is propitious to grow and hold the 2D GaNs without altering their intrinsic properties, in contrast to previously examined metal substrates.

This paper presents an approach to enhance Hf0.5Zr0.5O2 (HZO) ferroelectric orthorhombic phase (O-phase) formation via in situ NH3 plasma treatment. High-resolution non-disruptive hard x-ray photoelectron spectroscopy confirmed that O-phase formation can be enhanced by suppressed interfacial diffusion between HZO and the top TiN electrode. Additional N-bonding facilitated by NH3 treatment was shown to suppress the interaction between TiN and HZO, thereby reducing the formation of oxygen vacancies within HZO. It was shown to improve the reliability and ferroelectric performance (examined by the leakage current and positive-up-negative-down measurements) of HZO devices. After cyclic operations, NH3-treated ferroelectric FETs (FeFETs) exhibited stable transfer characteristics and memory windows, whereas untreated devices presented unstable behaviors. Our results demonstrate the efficacy of the proposed in situ NH3-treatment scheme in enhancing the stability of HZO-based FeFETs.

HfO2 has many favorable characteristics for use in energy conversion devices including high thermodynamic stability, good chemical stability in corrosive electrolytes, high refractive index, and wide bandgap. Here, we report surface passivation of a c-Si photocathode by ultrathin HfO2 prepared using atomic layer deposition as an effective approach for enhancing its photoelectrochemical (PEC) performance. The effect of the thickness of HfO2, deposition temperature, and annealing in forming gas on the passivation performance are systematically investigated. We demonstrate that the Si photocathode with a p+/n/n+ structure decorated with a Ni3N/Ni cocatalyst and an HfO2 interlayer follows a metal–insulator–semiconductor mechanism with thicker HfO2 films proving detrimental to the PEC performance. The Si photocathode passivated with a 1 nm HfO2 layer exhibits an enhancement in the onset potential by 100 mV, an applied-bias photon-to-current efficiency of 9%, and improved operational stability. This work provides insights into the application of HfO2 as a passivating layer for Si photoelectrodes for solar hydrogen production.

A divergent microstructure was fabricated by CMOS compatible processes on the central region of a Ge p i-n photodetector to enhance the residual tensile strain. Tunable biaxial tensile strain of ~0.22-1.01% was achieved by varying the geometrical factors, and it was confirmed by Raman measurements and finite element method (FEM) simulations. The suspended germanium membranes enhance the absorption across the C- and L-band (1,528–1,560 nm and 1,561–1,620 nm) and extend the cutoff wavelength to ~ 1,700-1,937 nm. The Ge absorption coefficient is enhanced by ∼4.2× to 2,951 cm−1 at 1,630 nm which is comparable with that of In0.53Ga0.47As. Furthermore, due to the varying strain distribution on the Ge mesa, each photodetector presents the location-determined wavelength-selective photoresponsivity characteristics. This work offers a promising approach for adjusting the absorption spectra of the photodetector by harnessing geometrically amplified biaxial strain. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version The work was financially supported by Singapore National Research Foundation under the Competitive Research Program (NRF–CRP19–2017– 01) and Ministry of Education (AcRF Tier 1 2019-T1- 002-040 (RG147/19 (S))).

Benefit from high quantum efficiency and low dark current, blocked-impurity-band (BIB) detectors have been the state-of-the-art choice in astronomy science. The temperature extrinsic-response-reduction mechanism in BIB detectors is vague for lack of pertinent research. We fabricated Si:P BIB detectors with a remarkable blackbody detectivity of 2 × 1012 cm · Hz1/2/W at 4 K, 2 V (blackbody 800 K). Both varying temperature optoelectronic characterization and calculated results overturn the common standpoint that focuses on ionization proportion. Instead, solid evidence indicates that the increase in the negative charge density according to temperature significantly influences the width of the depletion region until it totally vanishes beyond 20 K. The mechanism enriches the design thoughts of the BIB detector for improving its performance.

We report on a study that offers fundamental physical insight into an important phenomenon in solid state device physics, tunneling in Si/SiO2. We observe near-zero field magnetoresistance via spin-dependent trap-assisted-tunneling in both unpassivated and passivated Si/SiO2 and 28Si/28SiO2 metal–insulator–semiconductor (MIS) capacitors. A previous report, which utilized electrically detected magnetic resonance and NZFMR on these devices, indicates a surprising conclusion: the observed trap-assisted tunneling spectra are dominated by silicon dangling bonds back bonded to silicon at the Si/SiO2 interface, Pb0 and Pb1 centers. In this study, the four sets of samples are virtually identical, apart from the presence or absence of either 1H and 29Si. We observed a substantial narrowing of the NZFMR response with the removal of 29Si nuclei and a substantial broadening with the addition of 1H. Since superhyperfine interactions between 29Si nuclei Pb at the Si/SiO2 interface are a full order of magnitude stronger than such interactions involving silicon dangling bonds defects (E′ centers) within the oxide, the NZFMR results strongly suggest a response dominated by Si/SiO2 interface trap defects. With the introduction of 1H magnetic nuclei to the interface after a forming gas anneal, linewidths and lines shapes of Si/SiO2 and 28Si/28SiO2 MIS capacitors were nearly identical. However, the amplitude of the NZFMR response is greatly reduced by the introduction of hydrogen by a fraction about equal to the reduction in the interface trap density. Our results further indicate that the rate limiting step in trap-assisted tunneling is the interface to oxide trapping event.

In this study, the room temperature high-pressure oxidation technique is proposed to exquisitely manipulate the surface morphology and oxygen depth-profile of the tungsten-doped indium zinc oxide (InWZnO) film, and its influence on the switching characteristics is emphasized. Based on the atomic force microscope analysis, the smoother surface morphology of the InWZnO film after the high-pressure oxidation treatment is observed. Moreover, it is observed that the InWZnO film has significantly manipulated the oxygen vacancy depth-profile and improved the chemical properties after high-pressure oxidation treatment, according to the x-ray photoelectron spectroscopy depth profiling results. Compared with the control device, the device with high-pressure oxidation treatment exhibited highly uniform resistance states and set/reset repeatability. Finally, the mechanism of the effect of high-pressure oxidation treatment on the InWZnO film is completely examined according to the in-depth material analysis and physical model discussed.

Hf0.5Zr0.5O2 (HZO) has become one of the most popular HfO2 based ferroelectric thin films due to its huge potential to integrate low-cost high-density nonvolatile ferroelectric memory. Most researchers sandwiched the HZO between metals, such as TiN, and then adopted post-deposition high temperature anneal to improve the ferroelectricity and reliability of the film. In this work, the effect of a thin dielectric Al2O3 layer with different thicknesses to replace a metallic capping layer on the ferroelectric properties of a HZO (10 nm) thin film is evaluated, and we also compared the effects of TiN and W bottom electrodes on the properties of a capacitor. The results showed that the TiN/Al2O3 (1 nm)/HZO/W capacitor performed the best with a maximum 2Pr as high as 31.4 μC/cm2 at an electric field of ±3 MV/cm and very low leakage currents. In addition, the fatigue studies demonstrated the capacitor's excellent endurance properties with continuous cycling up to 1010 cycles. The use of an ultra-thin Al2O3 layer with excellent capping effects would significantly simplify the integration process of HfO2-based ferroelectric memory.

Mechanical strain plays a key role in the physics and operation of nanoscale semiconductor systems, including quantum dots and single-dopant devices. Here we describe the design of a nanoelectronic device where a single nuclear spin is coherently controlled via nuclear acoustic resonance (NAR) through the local application of dynamical strain. The strain drives spin transitions by modulating the nuclear quadrupole interaction. We adopt an AlN piezoelectric actuator compatible with standard silicon metal-oxide-semiconductor processing, and optimize the device layout to maximize the NAR drive. We predict NAR Rabi frequencies of order 200 Hz for a single $^{123}$Sb nucleus in a wide region of the device. Spin transitions driven directly by electric fields are suppressed in the center of the device, allowing the observation of pure NAR. Using electric field gradient-elastic tensors calculated by density-functional theory, we extend our predictions to other high-spin group-V donors in silicon, and to the isoelectronic $^{73}$Ge atom., 6 pages, 5 figures

Elemental antimony (Sb) has been carried out recently as a phase-change material to overcome composition segregation in a heavily cycled memory cell. Explosive crystal growth of Sb is desirable for fast operation speed in memory; however, poor thermal stability, i.e., fast spontaneous crystallization at room temperature, significantly impedes its applications. In this work, we designed a thermal stability enhanced “monatomic” Sb in a specific confined structure of [Sb(3 nm)/SiO2(5 nm)]32 and investigated its crystallization kinetics by using the ultrafast differential scanning calorimetry method. It was found that this nanoscale Sb exhibits appealing amorphous thermal stability with a crystallization activation energy of 2.68 eV and the temperature for 10-year data retention more than 361 K. Moreover, strong non-Arrhenius crystallization behavior with a high fragility index of 90 was unrevealed in Sb supercooled liquids, which has the maximum crystal growth rate of 2.17 m s−1 at 785 K. Thanks to the fast crystal growth rate and attractive thermal stability of this monatomic Sb, it could be one of the most important candidates for high-integrated on-chip memory without any composition segregation.

This paper presents the electrical conductivity data of copper along the gas branch of the binodal curve in the warm dense matter (WDM) regime as a function of mass density and temperature. All data are obtained using the underwater wire explosion technique, in which vaporized copper cools along the gas branch of the binodal curve during the period of current dwell after the wire explodes. Mass density and temperature are measured by fast imaging and optical spectroscopy, respectively. Combining these data with electrical measurements of the wire resistance, we obtain the conductivities of copper along the binodal curve in the WDM regime. The electrical conductivity data measured here are expected to be helpful for developing a more accurate and reliable theory of transport properties in the WDM regime.

We present experimental and theoretical results on the measurements of the oscillation frequency in a dipole trap based on the spin current in a sodium spinor Bose–Einstein condensate. The spin current is induced under different magnetic field intensities. The oscillation of the spin components in the dipole trap is strongly enhanced by a radio frequency pulse. Both theoretical analysis and experimental results demonstrate that this method can be used to efficiently measure the trap frequencies. Since this mechanism is independent of atomic species, this study is promising to be extended to rubidium and other optical-trappable quantum gases.

The ion storage mechanism and ion concentration play crucial roles in determining the electrochemical energy storage performances of multi-ion-based batteries and/or capacitors. Here, we take δ-MnO2-A2SO4 (A = Li, Na, K) as an example system to explore the physical and chemical mechanisms related to electrochemical energy storage using experimental analysis and first-principles calculations. Among the studied systems, superior capacitance performance is found in δ-MnO2-Li2SO4 due to excellent mobility (migration barrier 0.168 eV) of lithium ions. Better cycling stability appears in δ-MnO2-K2SO4, which is attributed to larger adsorption energy (−0.655 eV) between potassium ions and δ-MnO2. Moreover, compared with a pure Li2SO4 electrolyte, our calculations suggest that incorporation of moderate Na2SO4 or K2SO4 into the Li2SO4 electrolyte could considerably elongate the cycling lifetime. Overdose of Na+ or K+ is, however, adverse to the capacitance performance as verified by our experiments. We argue that the dominance role of Na+ or K+ ions played in the hybrid electrolyte originates from the larger formation enthalpy and adsorption energy of Na+ or K+ when reacting with δ-MnO2 compared with those of Li+. Our findings suggest that understanding of the ion storage mechanism can provide useful clues for searching the proper ion concentration ratio, which takes advantages of individual ions in multi-ion-based δ-MnO2 electrochemical energy storage devices.

Cubic boron nitride is an ultrawide-bandgap semiconductor with potential applications in high-power electronics, ultraviolet optoelectronics, and quantum information science. Many of those applications are predicated on the ability to control doping. Using hybrid-functional first-principles calculations, we systematically explore potential donors including group-IV (C, Si, and Ge) and group-VI (O, S, and Se) elements, as well as Li and F. We also address the role of compensation either by substitution on the wrong site or due to native point defects. We identify SiB and ON as promising dopants, as they have the lowest formation energies and do not suffer from self-compensation. However, compensation by boron vacancies, which act as deep acceptors, poses a challenge. We discuss strategies to mitigate these effects.

The dielectric functions of germanium–tin alloy thin-films, deposited by molecular beam epitaxy on bulk Ge substrates, with relatively high Sn contents from 15 to 27 at. %, were measured by variable angle spectroscopic ellipsometry over the wavelength range from 0.190 to 6 μm, using a combination of ultraviolet-visible and infrared ellipsometers. The band structure critical point energies, specifically the E1 and E1 + Δ1 optical transitions, were extracted from the measurements by a method of parametric oscillator modeling and second derivative analysis. With increasing Sn content, the transitions shifted to lower energies, and for alloys with less than 20% Sn, the numerical values agreed reasonably with predictions based on deformation potential theory that accounted for film strain. For the higher Sn alloys, the critical point energies from measurements agreed less well with deformation potential theory. These results provide information on the band structure of GeSn alloys with high Sn contents, which are increasingly important for long-wave infrared devices and applications.

High-performance dielectric capacitor represents an emerging technological goal for energy storage in modern electrical and electronic systems. In this work, we report a lead-free film capacitor based on the Bi(Mg1/2Ti1/2)O3 modified BiFeO3-Sr0.7Bi0.2TiO3 relaxor. A large recoverable energy storage density of 77.5 J/cm3, together with an efficiency of 56.1% is achieved in the film with 15 mol. % Bi(Mg1/2Ti1/2)O3 in composition. The film also exhibits excellent fatigue endurance with a reduction less than 3% over 1 × 108 cycles in both recoverable energy storage density and efficiency. Such good properties are ascribed to the improved electrical insulation and breakdown strength and the enhanced relaxor behavior by introducing the bismuth-based perovskite-like compound.

Ongoing active development of modern radio frequency electronic devices operating in the millimeter (V) band, such as fifth-generation wireless communications, demands new materials to control electromagnetic interference, compatibility, and reliability of such systems. This work investigates feasibility absorptive non-reflective thin coatings deposition on dielectric substrates using simultaneous magnetron co-deposition. For this, electromagnetic waves propagation in the millimeter band through in micrometer-thick Al–Si films of varied composition was studied. The co-deposition process was controlled by the ratio of sputtered atoms fluxes. Graded segregation was observed under certain parameters of the co-deposition process, resulting in a depth gradient of an aluminum content, as confirmed by the secondary ion mass spectrometry study. A qualitative model was proposed involving aluminum-induced silicon recrystallization happening in the course of a known aluminum interlayer exchange process. The observed Al–Si segregation effect in micrometer-thick films allows for preparation of the non-reflective and absorptive material for operation in the V-band with reflection losses more than 10 dB and transmission losses around 5 dB in the bandwidth of up to 20 GHz.

Photoelectrochemical water-splitting is a possible path toward sustainably produced hydrogen, which is a potential solar fuel of the future. Complex tuning of material properties is necessary to further enhance efficiency and, therefore, ensure economic viability of this process. In this study, the influence of Ti-site substitution in the perovskite-related oxynitride LaTi(O,N)3 is investigated. Oxide materials, La2Ti2-2xNb2xO7±δ without and with a substitution of up to 8% of the Ti-sites, are synthesized and, subsequently, transformed into the corresponding phase pure oxynitrides, LaTi1-xNbx(O,N)3±δ. The incorporation of Nb is confirmed via x-ray diffraction and energy dispersive spectroscopy. Changes in morphology, nitrogen content, optical properties, and charge carrier density are investigated using scanning electron microscopy, gas adsorption, thermal gravimetric analysis, and UV-vis and electrochemical impedance spectroscopies. Charge compensation of the positive charge introduced by Nb5+ via additional N3− incorporation is identified as a mechanism that occurs during thermal ammonolysis and results in an increased N content in substituted compounds, probably preventing charge carrier density increase. An improvement of up to 30% of the photocurrent density at 1.23 V vs RHE is achieved for x = 0.01 in comparison to unsubstituted LaTi(O,N)3. The performance increase in this material is related to a reduction in (crystalline) defects at low substitution degrees. These results underline the necessity to tune the synthesis conditions carefully for material design.

For perovskite solar cells with carbon electrodes (CPSCs) prepared using undoped hole transport materials and commercial carbon pastes, the poor interfacial carrier transport performance hinders the efficiency improvement. Herein, the use of additive 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) not only plays the role of passivating defects and assisting film formation but also regulates one to obtain more favorable interfacial energy band bending and energy level matching, while forming charge transfer complexes with perovskites due to its strong electron-withdrawing ability. Having all these functions at the same time makes CPSCs with F4TCNQ addition obtain high quality, low defect density films with suppressed non-radiative recombination, along with extremely fast carrier separation and extraction capabilities. Together with the optimization of the electron transport layer, the prepared CPSCs obtained an enhanced photovoltaic conversion efficiency of 15.1% and a VOC of 1.07 V with long stability.

Since the absorption zone of ultraviolet (UV) photons with high energy is limited to a few tens of nm on the surface, the high defect density caused by the processes, such as ion implantation, leads to a weak response of the silicon avalanche photodiode (APD) in the ultraviolet band. In this work, the integration of the inorganic perovskite quantum dots (QDs) film by drop-casting as the down-shifting layer is reported for enhancing the UV response of Si APD. The light generated current increases 100% under the 365 nm light emitting diode. The response of the Si APD is improved in the entire ultraviolet band. In particular, the responsivity of APD is increased by 78% at 340 nm with an exceedingly EQE of 92%. In summary, the perovskite QDs film as a down-shifting layer provides an effective and low-cost method to improve the UV response of Si APD.

External quantum efficiency (EQE), color rendering index (CRI), color correlated temperature (CCT), and spectral stability are key challenges for constructing high-performance white organic light-emitting diodes (WOLEDs) with a simple device structure. Herein, in order to resolve these issues, we primarily employed a thermally activated delayed fluorescence (TADF) emitter of CzAcSF as a host emitter and a dinuclear platinum (III) complex (Pt-1) as a guest emitter to construct solution-processed single-emitting layer WOLEDs at low guest concentrations of 0.75–1.50 wt. %. Thanks to their broad coverage of visible spectra, efficient energy transfer, and weak charge trap of Pt-1, the optimized WOLEDs showed an increasing EQE of 11.93% and a current efficiency of 30.76 cd/A with a high CRI of 75 and a CCT of 5210 K. Furthermore, the stable electroluminescent spectra with CIE (commission internationale de L'Eclairage) coordinate deviations of Δx = 0.022 and Δy = 0.015 were exhibited. This is an outstanding example for high-performance WOLEDs via employing a TADF host-sensitized low-concentration dinuclear platinum (III) complex simultaneously with high efficiency, CRI, CCT, and color stability.

The non-equilibrium state between magnons and phonons is the key to understand the spin-caloric phenomena. We developed a unique optical reflectometry technique to spatially resolve Kerr angle ( θK) and optical reflectance ( R) in a magnetic insulator—thulium iron garnet (TmIG). The TmIG was subjected to a thermal gradient to estimate populations of thermally excited magnons and phonons through the variation of θK and R. The results showed that the spatial gradient of θK is different from that of R, indicating the non-equilibrium state between magnons and phonons. Particularly, the characteristic decay length of θK was significantly influenced by the heating power and the magnetic field, suggesting non-linear magnon scattering in a high magnon density regime. Our work not only provides a scheme to investigate the spatial profiles of magnons and phonons but also reveals the magnon–phonon non-equilibrium in TmIG. Hence, this report will stimulate further studies based on magnon–phonon non-equilibrium such as a transverse spin Seebeck effect and Bose–Einstein condensation.

In this Letter, we present the excellent negative differential resistance (NDR) characteristics of AlN/GaN double-barrier resonant tunneling diodes (RTDs) in which the active layers are grown by molecular beam epitaxy on thick GaN-on-sapphire templates manufactured by metal-organic chemical vapor deposition. Here, indium flux is introduced as surfactant to reduce the interface roughness and improve the sharpness of heterointerface during epitaxial growth of AlN/GaN/AlN quantum well. The processed device with a top collector diameter of 1 μm size demonstrates a record peak current density of 1039 kA/cm2 while simultaneously featuring a peak-to-valley current ratio of 1.23 at room temperature, excellent achievements among all the reported GaN-based RTDs on any substrates. In addition, no degradation of device performance together with free of hysteresis is observed for the 1000 times consecutive up-to-down voltage sweeps under forward bias. These remarkable achievements are attributed to the marked improvement in heterointerface quality of AlN/GaN/AlN double-barrier quantum well by adopting indium as surfactant during epitaxial growth as clarified by transmission electron microscopy analysis, which dramatically suppresses the interface roughness scattering and elements interdiffusion, thus significantly improving the NDR signatures in current–voltage curves. The obtained results in this work illustrate that indium-surfactant added epitaxy technique turns out to be a promising approach for the modulation of vertical electron resonant tunneling in III-nitride heterostructures and realization of highly reproducible and reliable AlN/GaN double-barrier RTDs, in favor of implementation for future high-power solid-state electronics operating in terahertz spectra.

All-inorganic CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (NCs) are the most promising next generation photoelectric materials owing to their excellent properties. Although embedding perovskite NCs into a glass matrix improves their stability, different applications require perovskite nanocrystal glasses (PNGs) with different properties. In this work, we controlled the network structure of the precursor glass by changing the content of ZnO (3.8–11.4 mol. %) in the raw materials, thus inhibiting the direct precipitation of CsPbCl2Br NCs in the glass (i.e., the self-crystallization process), and obtained samples with local emission and high transmittance. In addition, we incorporated rare-earth (RE) Yb3+ into a CsPbCl2Br PNG to achieve efficient ultraviolet (UV) to near-infrared quantum cutting emissions and boost the UV response of silicon photodetectors (PDs). Finally, after combining the Yb3+-doped CsPbCl2Br PNG on the Si PDs, the responsivity of the latter increased to 0.014 A/W at 320 nm, which is 14 times higher than that of the bare Si PDs. Moreover, Si PDs based on Yb3+-doped CsPbCl2Br PNG exhibited excellent photocurrent stability.

A highly relaxed InGaN buffer layer was demonstrated over a full two-inch c-plane sapphire substrate by metalorganic chemical vapor deposition. The InGaN buffer layer was grown on a 100 nm GaN decomposition stop layer with a 3 nm thick high indium composition InGaN underlayer. After thermal decomposition of the underlayer at 1000 °C, a 200 nm thick In0.04Ga0.96N buffer showed 85% biaxial relaxation measured by a high resolution x-ray diffraction reciprocal space map. When used as a pseudo-substrate for the regrowth of InGaN/InGaN multi-quantum wells, the sample showed a 75 nm red-shift in room temperature photoluminescence when compared to a co-loaded GaN template reference. The longer emission wavelength is associated with higher indium incorporation in the InGaN layers from the lessening of the compositional pulling effect caused by compressive strain. Using this technique, a simple red light emitting diode was demonstrated with an active layer growth temperature of 825 °C and a peak wavelength of 622 nm at a current density of 20 A cm−2. This work represents a unique method to relax a III-nitride based layer over a full substrate.

A resonant absorber enables low-temperature sintering of InZnO sol–gel films with low-energy-density intense pulse light (IPL) irradiation (1 J/pulse). A back-gate structure, incorporated with a resonant absorber, exhibits effective light absorption. A device fabricated based on such a gate structure and sintered with irradiation of 50 pulses (∼50 J/cm2) demonstrates good electrical properties with a mobility of 0.34 cm2/V s and an on–off ratio of 106 and a substrate temperature under 210 °C, showcasing that employing a resonant absorber could enable low-temperature sintering of sol–gel films with low-energy-density irradiation. Further x-ray photoelectron spectroscopy analysis of the oxygen and nitrogen peaks indicates that IPL irradiation facilitated sol–gel reactions in films.

We report on 193 nm excimer laser-based liftoff (LLO) of Al0.26Ga0.74N/GaN high electron mobility transistors (HEMTs) with thick (t > 10 μm) AlN heat spreading buffer layers grown over sapphire substrates. The use of the thick AlN heat spreading layer resulted in thermal resistance ( Rth) of 16 K mm/W for as-fabricated devices on sapphire, which is lower than the value of ∼25–50 K mm/W for standard HEMT structures on sapphire without the heat-spreaders. Soldering the LLO devices onto a copper heat sink led to a further reduction of Rth to 8 K mm/W, a value comparable to published measurements on bulk SiC substrates. The reduction in Rth by LLO and bonding to copper led to significantly reduced self-heating and drain current droop. A drain current density as high as 0.9 A/mm was observed despite a marginal reduction of the carrier mobility (∼1800 to ∼1500 cm2/V s). This is the highest drain current density and mobility reported to-date for LLO AlGaN/GaN HEMTs.

Metal-insulator transitions (MIT),an intriguing correlated phenomenon induced by the subtle competition of the electrons' repulsive Coulomb interaction and kinetic energy, is of great potential use for electronic applications due to the dramatic change in resistivity. Here, we demonstrate a reversible control of MIT in VO2 films via oxygen stoichiometry engineering. By facilely depositing and dissolving a water-soluble yet oxygen-active Sr3Al2O6 capping layer atop the VO2 at room temperature, oxygen ions can reversibly migrate between VO2 and Sr3Al2O6, resulting in a gradual suppression and a complete recovery of MIT in VO2. The migration of the oxygen ions is evidenced in a combination of transport measurement, structural characterization and first-principles calculations. This approach of chemically-induced oxygen migration using a water-dissolvable adjacent layer could be useful for advanced electronic and iontronic devices and studying oxygen stoichiometry effects on the MIT., 16 pages, 4 figures

InP channel planar and vertical MOSFETs utilizing atomic layer deposition of a TiN/Ru gate are fabricated. The performance of the TiN/Ru gate is compared to a Ru-only gate based on the C–V characteristics of MOS (metal–oxide–semiconductor) capacitors and peak transconductance ( gm) and subthreshold swing ( SS) in planar MOSFETs. Compared to devices with the conventional Ni/Au gate metal, these have a 70 mV/dec SS [Tseng et al., in Device Research Conference (IEEE, 2019), pp. 183–184.] and a long gate length; TiN/Ru gate devices exhibit an average 68 mV/dec SS, a record low value of InP, suggesting a high quality, low-damage high-k/InP interface. A record high peak gm of 0.75 mS/μm at VDS = 0.6 V on an InP channel is achieved in a planar gate length ( Lg)= 80 nm device. A vertical MOSFET shows a reasonably conformal Ru coverage of the vertical fin and a high 0.42 mS/μm peak gm for a Lg = 50 nm device. The results of planar and vertical MOSFETs show that TiN/Ru gate metallization via atomic layer deposition is promising for non-planar III–V MOS devices.

Using the semibulk approach, p-InxGa1−xN semibulk (p-SB) templates were grown with an indium content ranging from 2.4% to 15.2% via metalorganic chemical vapor deposition. When compared to optimized bulk p-GaN, the hole concentration in p-SB with an In content of ∼15.2% increased by two orders of magnitude from 5.22 × 1017 to 5.28 × 1019 cm−3. The resistivity and mobility of the templates decreased gradually from 3.13 Ω · cm and 3.82 cm2/V s for p-GaN to 0.24 Ω · cm and 0.48 cm2/V s for p-SB with an In content of 15.2%. Temperature dependent Hall measurements were conducted to estimate the activation energy of the p-SB template. The p-SB with the In content of ∼15.2% is estimated to have an activation energy of 29 meV. These heavily doped p-SB templates have comparable material qualities to that of GaN. The atomic force microscopy height retraces of p-SB films show device quality surface morphology, with root mean square roughness ranging from 2.53 to 4.84 nm. The current results can impact the performances of several nitride-based devices, such as laser diodes, LEDs, solar cells, and photodetectors.

A high-entropy alloy Fe10Co10Ni10Cr10Mn60 ribbon catalyst with a face-centered cubic structure was designed by using Co and Ni as the main catalytic elements and combining various co-catalytic elements, such as Fe, Mn, and Cr. Substantial element selective corrosion occurs during the acid solution corrosion process, which induces the exposure of many Co and Ni atoms, increases the specific surface area, and further results in the formation of many vacancies and dislocations. This unique structure generates a positive electron effect, that is the peaks of Ni2p3/2 and Co2p3/2 shift to lower binding energies, namely, approximately 1 eV for Ni and 0.8 eV for Co, indicating the Co and Ni enrich electrons. The catalyst shows an excellent catalytic performance for the hydrolysis of NaBH4 after corrosion for 90 s, whose hydrogen production rate approaches 18.46 l/(m2·min). This work opens up a direction for the application of the macroscopic scale high-entropy alloy in the catalytic hydrogen field.

Green hydrogen is currently enjoying a worldwide momentum due to its potential in supporting the United Nations Sustainable Development Goals. It is one of key technologies toward the establishment of a global low-carbon energy infrastructure. As a viable solution to achieve green hydrogen from renewable sources such as wind and solar powers, the process of proton exchange membrane (PEM) water electrolysis enables scalable stacked devices and systems for high pressure hydrogen production. By developing a catalyst-coated proton exchange membrane, we constructed membrane electrode assemblies (MEAs) and assembled them into a five-cell stack device to optimize the materials and components. After device characterization and optimization, a 20 kW PEM water electrolysis system was built, which, under high pressure operating conditions, exhibited favorable hydrogen production performance with 82.9% energy efficiency at the current density of 1000 mA/cm2 and reaction temperature of 70 °C. The resulting hydrogen production rate of the system with catalyst-coated membranes reached 3.09 N m3/h, while the power consumption for hydrogen production was 4.39 kWh/N m3. The results indicate the feasibility of PEM water electrolysis technology for green hydrogen production, for which we envision development into commercial applications in the near future.

In this study, the influence of the HfOxNy interfacial layer (IL), interposed between the atomic layer deposited ferroelectric (FE) Hf0.5Zr0.5O2 thin film and TiN top electrode, on the FE properties of such a film was examined. The HfOxNy IL decreased the relative proportion of the non-FE monoclinic phase, possibly due to the N-doping effect. Furthermore, the oxidation of the TiN top electrode was also suppressed by the sacrificial oxidation of the HfOxNy IL during the rapid thermal process. As a result, the double remanent polarization of a Hf0.5Zr0.5O2 thin film could be enhanced from 40.2 to 48.2 μC/cm2 by the positive-up-negative-down test, and its degradation by fatigue during the endurance test can also be decreased. This result demonstrates the significance of interfacial engineering to optimize the FE properties of Hf0.5Zr0.5O2 films.

In situ etching using Ga flux in an ultra-high vacuum environment like molecular beam epitaxy is introduced as a method to make high aspect ratio three-dimensional (3D) structures in β-Ga2O3. Etching of β-Ga2O3 due to excess Ga adatoms on the epilayer surface had been viewed as non-ideal for epitaxial growth especially since it results in plateauing and lowering of the growth rate. In this study, we use this well-known reaction from epitaxial growth to intentionally etch β-Ga2O3. We demonstrate etch rate ranging from 2.9 to 30 nm/min with the highest reported etch rate being only limited by the highest Ga flux used. Patterned in situ etching is also demonstrated and used to study the effect of fin orientation on the sidewall profiles and dopant (Si) segregation on the etched surface. Using in situ Ga etching, we also demonstrate 150 nm wide fins and 200 nm wide nanopillars with high aspect ratio. This etching method could enable future development of highly scaled vertical and lateral 3D devices in β-Ga2O3.

Tin oxides are the most promising electron transport layers in perovskite solar cells. An ambipolar carrier transport property has been recently demonstrated which enables a simple interconnection structure for all-perovskite tandem solar cells. However, the underlying mechanism for its ambipolar behavior is unclear, which cannot be explained by the intrinsic defects in SnO2−x. Here, by using density functional theory calculations, we unveil the origin of the ambipolar carrier transport of non-stoichiometry SnO2−x with a structure of SnO embedded in the SnO2 matrix. The hybridization of O 2p and Sn 5s orbitals of SnO introduces mid-gap states in the bandgap of SnO2, enabling hole transport property for SnO2−x when x is > 0.2. Increasing the percentage of SnO in SnO2−x significantly enhances the hole transport capability of SnO2−x due to the enlarged Sn–O–Sn angles that increase orbital overlapping between O and Sn atoms, thus providing strategies for the further tuning of the carrier transport properties of SnO2−x by compositional and structural designs.

Silicon-based photodetectors in photoelectric sensing applications are crucial. In the previous studies of the piezo-phototronic effect on performance modulation of Si/ZnO heterojunctions, the majority is based on a rigid silicon substrate and a ZnO one-dimensional nanostructure, causing incompatibility with advanced semiconductor processing technology as well as the limitation in the field of wearable application. Here, flexible p-Si/n-ZnO film heterojunction photodetectors have been constructed by sputtering ZnO films on chemically thinned Si substrates. Under 405 nm light illumination and at −0.5 V bias, the reverse photocurrent of the heterojunction under the −0.73‰ compression strain increased by 50.36% compared to that under a strain-free state, while the reverse photocurrent for the same device under 0.73‰ tensile strain decreased by 29.2% compared to that under the strain-free state. The introduction of a flexible silicon wafer realizes a bidirectional photocurrent response regulation, which lies in the fact that the strain-induced piezo-potential governs the local energy band structure at the heterojunction interface and, thus, influences the carrier transport in the heterojunction region. The COMSOL simulation results further verify the evolution of the energy band structure at the heterojunction interface at different strain states. This work provides a strategy to design silicon-based optoelectronic devices via the piezo-phototronic effect of a ZnO film.

A single hydrogen nanograin has been modeled here to explore the evolution of its structural properties under compression. It is revealed to change from the molecular-insulator (P63/mmc) to the molecular-metal phase (Pca21) in the form of the hollow spherical shell at a pressure much lower than the one for metallization of bulk hydrogen. The compression is demonstrated to induce both the structure transition and the charge transfer between atoms so that the infrared bands are determined both by the structure and by the atomic-charge distribution. The hydrogen nanograins are, thus, proposed to change more easily from the insulator to metallic hydrogen with respect to bulk hydrogen. Our findings open an alternative route to creating metallic hydrogen.

As the first-generation semiconductor, silicon (Si) exhibits promising prospects in thermoelectric (TE) convention application with the advantages of un-toxic, abundant, robust, and compliant to the integrated circuit. However, Si-based TE materials are always implemented for high-temperature application and deficient at room temperature (RT) ambience. This study displays an N-type Si1−x−yGexSny thin film by carrying out the strategy of metallic modulation doping for enhancing its power factor (PF). It was distinct to observe the extra carriers poured from the precipitated Sn particles without prominent degradation of mobility while sustaining appreciable thermal conductivity. The PF of 12.21 μW cm−1 K−2 and zT of 0.27 were achieved at 125 °C, which illustrated the significant potential for implementation at near RT ambiance.

Ferroelectric Hf0.5Zr0.5O2 is a prime candidate material for integrated HfO2-based ferroelectric devices due to its simple composition, low crystallization temperature, and significant remanent polarization. It is particularly promising for integrated pyroelectric devices used in infrared sensing and energy harvesting, although the appearance of nonferroelectric tetragonal and monoclinic phases should be avoided to achieve high-performance pyroelectric sensors. Both nonferroelectric phases are strongly influenced by the Hf0.5Zr0.5O2 film thickness and annealing temperature. The sensitivity of the pyroelectric coefficient on film thickness is investigated with atomic layer-deposited Hf0.5Zr0.5O2 films within a 10–30 nm thickness range. The films are capped with TiN and undergo post-metallization anneals at 450 °C and 600 °C. An optimum pyroelectric coefficient of −56 μC K−1 m−2 is found in the 15 nm thick Hf0.5Zr0.5O2. The pyroelectric coefficient is found to be sensitive to thickness-dependent depolarization effects and monoclinic phase growth. Ferroelectric, dielectric, and pyroelectric properties are improved with a lower annealing temperature, demonstrating the back-end-of-line compatibility of Hf0.5Zr0.5O2 pyroelectric devices.

An oxygen-based ionic synaptic transistor (O-IST) is a promising synaptic element for neuromorphic computing. In this study, we demonstrated that the density of the electrolyte plays a key role in achieving excellent synaptic characteristics in an O-IST. In a Pr0.7Ca0.3MnO3-based O-IST, we precisely controlled the density of the HfOx electrolyte and found that a low-density electrolyte could improve the ion mobility. Owing to the improved ion mobility and controlled ion migration, we demonstrated that excellent synaptic characteristics, such as a wide dynamic range, linear weight update, low operating voltage operations, and stable cyclic operation, were achieved. Finally, we confirmed an improved pattern recognition accuracy using an O-IST with an HfOx electrolyte of optimal density.