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Abstract Vacuum ultraviolet (VUV) light sensing shows great potential applications in the space science, materials, biophysics, and plasma physics. In this work, an all-optical detection method is proposed for VUV sensing by constructing an optical fiber-end Fabry-Pérot interferometer based on a single aluminum nitride (AlN) microwire. Compared with the traditional electrical devices, this all-optical detection method overcomes the difficulties like the fast response and electromagnetic interference immunity in detecting VUV bands at the present stage, and improves the response speed. The proposed device shows the excellent performance of VUV detection, with the static sensitivity of 1.03 nm/(W·cm−2), response rise time of down to 10 µs, and decay time of 0.64 ms. Beneficial from the excellent radiation resistance of AlN microwires and UV resistance of silica fibers, the proposed device is expected to have the good stability and potential applications in the fields of the solar physics and space exploration.

Abstract The battery swapping mode is a promising way for electric vehicles (EVs) to participate in power grid frequency regulation. However, the operation mechanism and the uncertainty management in the process still lack research. Aiming at this issue, this paper proposes a day‐ahead bidding strategy for the battery swapping and charging system (BSCS) providing regulation reserve capacity in the ancillary service market. Firstly, a new BSCS‐based regulation model is established. Then, an ambiguity set based on Kullback–Leibler (KL) divergence is used to manage the uncertainty of regulation signals and battery swapping demands. Furthermore, a boundary expectation approach is proposed to turn the problem into robust optimization. Finally, after using the extreme scenario method (ESM) to generate extreme scenarios, a duality‐free column‐and‐constraint generation (C&CG) algorithm is employed to solve the problem. The case studies demonstrate that BSCS can provide economical and robust reserve capacity bidding plans in the day‐ahead market with the proposed strategy. At the same time, the BSCS‐based regulation service is simulated with the battery development trend in the future, and suggestions are given.

Aluminum nitride (AlN) exhibits excellent high-temperature resistance, chemical stability, and a wide bandgap, making it a prime candidate material for deep ultraviolet detectors. In this study, a modified metal–semiconductor–metal (MSM) photodetector using titanium (Ti) electrodes and millimeter-scale AlN bulk polycrystals grown through physical vapor transport is developed, demonstrating photoresponse to light from visible to vacuum ultraviolet. An additional tungsten (W) electrode is designed on the backside of the device, transforming it into a W-MSM device. A proper bias to the W electrode (VW) is found valid to boost the performance of the photodetector. Representatively, with a V of 20 V and VW of −12 V applied, the device achieves improvements in responsivity (R), detectivity (D*), and external quantum efficiency of 112.84%, 30.5%, and 112.84%, respectively, to 532 nm light and 123.18%, 36.84%, and 123.18%, respectively, to 193 nm light. Furthermore, it is found that with the total voltage being instant, optimizing the distribution of voltage between the Ti electrode and the W electrode would induce a better photoresponse than applying voltage solely to the Ti electrode (VW = 0 V). The reason is elaborated through modeling the voltage distribution in the device, revealing the particular role of the bulk semiconductor in this feature. This research provides a facile and innovative approach to developing low-power photodetectors for bulk materials.

In silicon carbide (SiC) planar insulated-gate bipolar transistor (IGBT), a large distance between neighboring p-bodies is beneficial to enhance the on-state conductivity modulation, but will expose the gate oxide to high electric field in off-state. With p-bodies placed closer, the gate oxide field is reduced, but the conductivity modulation is suppressed. In this work, a new SiC planar IGBT with oxide shield is proposed and studied by TCAD simulations. The proposed SiC IGBT achieves improved trade-off between on-state voltage drop $(V_{\mathrm{ ON}})$ and maximum gate oxide electric field $(E_{\text {ox-m}})$ . When a quite larger distance between neighboring p-bodies is adopted in the proposed SiC IGBT, a low $V_{\mathrm{ ON}}$ is obtained, while the $E_{\text {ox-m}}$ can be kept at a small value with the oxide shielding structures protecting the gate oxide. Switching characteristics are also studied, and the proposed SiC-IGBT delivers much better trade-off between turn-off energy loss $(E_{\mathrm{ OFF}})$ and $V_{\mathrm{ ON}}$ than the conventional SiC planar IGBT.

In the face of multiple failures caused by extreme disasters, the power and communication sides of the distribution network are interdependent in the fault recovery process. To improve the post-disaster recovery efficiency of the distribution network, this paper proposes a coordinated optimization strategy for distribution network reconfiguration and repair, which integrates the power and communication aspects. First, the recovery process is divided into islanding–reconfiguration and dynamic emergency repair. The coupling relationship between power and communication is considered; that is, power failure may cause communication nodes to lose power, and communication failure may affect the effective operation of remote control devices. Based on this, the fault recovery process is optimized with the objective of maximizing load transfer and direct recovery while introducing a stochastic model predictive control method to handle the uncertainty of distributed power generation by rolling optimization of typical scenarios. Finally, the effectiveness of the proposed strategy is verified using an improved IEEE33-node distribution network system. The simulation results show that the proposed method can recover power to the maximum extent and reduce loss while ensuring the safe and stable operation of the distribution system.

The improved resistively-heated furnace with two heaters established a vertical thermal gradient to control nucleation during AlN single crystals Physical Vapor Transport (PVT) growth on polycrystal tungsten substrates. During the high temperature (> 1850 °C) heating process, the reverse temperature field (i.e., the temperature difference between the sublimation zone and the crystalline zone ΔT 1850 °C) cooling was fulfilled to avoid recrystallization on grown AlN crystal. AlN single crystals made through the method were characterized by X-ray diffractions (XRD) and Raman spectroscopy.

An aluminum nitride (AlN) Schottky barrier diode (SBD) was fabricated on a nonpolar AlN crystal grown on tungsten substrate by physical vapor transport. The Ni/Au–AlN SBD features a low ideality factor ${n}$ of 3.3 and an effective Schottky barrier height (SBH) of 1.05 eV at room temperature. The ideality factor ${n}$ decreases and the effective SBH increases at high temperatures. The temperature dependences of ${n}$ and SBH were explained using an inhomogeneous model. A mean SBH of 2.105 eV was obtained for the Ni–AlN Schottky junction from the inhomogeneity analysis of the current–voltage characteristics. An equation in which the parameters have explicit physical meanings in thermionic emission theory is proposed to describe the current–voltage characteristics of inhomogeneous SBDs.

This paper focuses on the detailed investigation of the structural and electronic properties of wurtzite AlN crystals doped by Li with and without oxygen with the first principles calculation. All the calculations have exhibited significant structural distortions. Compared with the monoclinic doping, the oxygen codoping has improved the structure deformation and lowered the formation energy of Li dopants. The calculated electronic density of states (DOS) reveals that all doping configurations still preserve semiconductor characteristics. The states around the valence band maximum cross the Fermi level, which implies p-type doping. The induced extra levels are extremely localized and flat in Li-doped AlN while much more delocalized in oxygen codoped models. The mono-doping of Li is in general energetically unfavorable while the codoping improves the formation and makes the intercalation of Li more stable in AlN. According to the results, the codoping configuration of Li with O in AlN has provided a useful way of modifying the corresponding properties.

The below bandgap optical transitions of an aluminum nitride (AlN) crystal grown on a tungsten (W) substrate by physical vapor transport (PVT) are investigated by below-bandgap-excited photoluminescence (PL) spectroscopy and first-principles calculations. Oxygen (O) is the only impurity in the AlN-on-W crystal grown by PVT. By analyzing the excitation-power-, excitation-photon-energy-, and temperature-dependence of the PL spectra, the emission peaks of defect complexes involving aluminum vacancy (VAl) and substitutional oxygen (ON) with different spatial and atomic configurations, i.e., VAl–ON and VAl–2ON with ON featuring axial or basal configurations, are identified. It is revealed that two different charging states coexist in thermal equilibrium for each configuration of VAl–ON complexes. The optical transitions between the conduction band and (VAl–ON)2− and/or (VAl–2ON)1− contribute the UV emissions and those between the valence band and (VAl–ON)1− or (VAl–2ON)0 contribute the red emissions.

Solar to fuel energy conversion is one of the momentous topics nowadays considering the urgent demand for clean energy supplies. In this work, the tunable electronic and optical properties of III-nitride/ZnO 2D/2D heterostructures (including GaN/ZnO, AlN/ZnO, and GaN/AlN) by strain engineering were investigated by first-principles calculations. The studied heterostructures feature a small interlayer distance, with the cation of one layer directly above the anion of the other layer, and vice versa. This leads to a strong binding energy and interlayer coupling across the heterostructure. The built-in field induced by the charge redistribution facilitates the photoexcited carrier migration, which is beneficial to the photocatalytic water splitting application. The stable III-nitride/ZnO heterostructures exhibit decent band edge positions with biaxial strain engineering and feature an enhancement of optical absorption under tensile strain. Our results indicate that the III-nitride/ZnO 2D/2D heterostructures are promising photocatalysts for solar to hydrogen generation by water splitting.

A new silicon carbide (SiC) planar-gate insulated-gate bipolar transistor (IGBT) is proposed and comprehensively investigated in this paper. Compared to the traditional SiC planar-gate IGBT, the new IGBT boasts a much stronger injection enhancement effect, which leads to a low on-state voltage (VON) approaching the SiC trench-gate IGBT. The strong injection enhancement effect is obtained by a heavily doped carrier storage layer (CSL), which creates a hole barrier under the p-body to hinder minority carriers from being extracted away through the p-body. A p-shield is located at the bottom of the CSL and coupled to the p-body of the IGBT by an embedded p-MOSFET (metal-oxide-semiconductor field effect transistors). In off-state, the heavily doped CSL is shielded by the p-MOSFET clamped p-shield. Thus, a high breakdown voltage is maintained. At the same time, owing to the planar-gate structure, the proposed IGBT does not suffer the high oxide field that threatens the long-term reliability of the trench-gate IGBT. The turn-off characteristics of the new IGBT are also studied, and the turn-off energy loss (EOFF) is similar to the conventional planar-gate IGBT. Therefore, the new IGBT achieves the benefits of both the conventional planar-gate IGBT and the trench-gate IGBT, i.e., a superior VON-EOFF trade-off and a low oxide field.

Seed crystals are the prerequisite for the growth of high quality and large size aluminum nitride (AlN) single crystal boules. The physical vapor transport (PVT) method is adopted to grow AlN seed crystal. However, this method is not available in nature. Herein, the temperature field distribution in the PVT furnace was simulated using the numerical analysis method to obtain free-standing and large-size seeds. The theoretical studies indicate that the temperature distribution in the crucible is related to the crucible height. According to the theory of growth dynamics and growth surface dynamics, the optimal thermal distribution was achieved through the design of a specific crucible structure, which is determined by the ratio of top-heater power to main-heater power. Moreover, in our experiment, a sole AlN single crystal seed with a length of 12 mm was obtained on the tungsten (W) substrate. The low axial temperature gradient between material source and substrate can decrease the nucleation rate and growth rate, and the high radial temperature gradient of the substrate can promote the expansion of crystal size. Additionally, the crystallinity of the crystals grown under different thermal field conditions are analyzed and compared. The Raman results manifest the superiority of the thermal inversion method in the growth of high quality AlN single crystal.

The application of conventional power metal-oxide-semiconductor field-effect transistor (MOSFET) is limited by the famous one-dimensional “silicon limit” (1D-limit) in the trade-off relationship between specific on-resistance (RSP) and breakdown voltage (BV). In this paper, a new power MOSFET architecture is proposed to achieve a beyond-1D-limit RSP-BV trade-off. Numerical TCAD (technology computer-aided design) simulations were carried out to comparatively study the proposed MOSFET, the conventional power MOSFET, and the superjunction MOSFET. All the devices were designed with the same breakdown voltage of ~550 V. The proposed MOSFET features a deep trench between neighboring p-bodies and multiple p-islands located at the sidewall and bottom of the trench. The proposed MOSFET allows a high doping concentration in the drift region, which significantly reduces its RSP compared to the conventional power MOSFET. The multiple p-islands split the electric field into multiple peaks and help the proposed MOSFET maintain a similar breakdown voltage to the conventional power MOSFET with the same drift region thickness. Another famous device technology, the superjunction MOSFET (SJ-MOSFET), also breaks the 1D-limit. However, the SJ-MOSFET suffers a snappy reverse recovery performance, which is a notorious drawback of SJ-MOSFET and limits the range of its application. On the contrary, the proposed MOSFET presents a superior reverse recovery performance and can be used in various power switching applications where hard commutation is required.

The state-of-the-art silicon insulated-gate bipolar transistor (IGBT) features a trench gate, since it enhances the conductivity modulation. The SiC trench IGBT, however, faces the critical challenge of a high electric field in the gate oxide, which is a crucial threat to the device’s reliability. In this work, we explore the possibility of using a SiC planar IGBT structure to approach high performance to the level of a SiC trench IGBT, without suffering the high gate oxide field. The proposed SiC planar IGBT features buried p-layers directly under the p-bodies, and thus can be formed using the same mask set. The region between the buried p-layer and the p-body is heavily doped with n-type dopants so that the conductivity modulation is improved. Comprehensive TCAD simulations have been carried out to verify this concept, and the simulation results show the new SiC planar IGBT exhibits a high performance comparable to the trench IGBT, and also exhibits a low gate oxide field.

The improved resistively-heated furnace with two heaters established a vertical thermal gradient to control nucleation during AlN single crystals Physical Vapor Transport (PVT) growth on polycrystal tungsten substrates. During the high temperature (> 1850 °C) heating process, the reverse temperature field (i.e., the temperature difference between the sublimation zone and the crystalline zone ΔT < 0) was obtained to reduce the number of nuclei on the tungsten substrate. During growth, the proper positive values of ΔT T were chosen to content the supersaturation values (0.25 < S < 0.3). The reverse temperature condition during high temperature (> 1850 °C) cooling was fulfilled to avoid recrystallization on grown AlN crystal. AlN single crystals made through the method were characterized by X-ray diffractions (XRD) and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

In this work, the Schottky-on-heterojunction light-emitting diodes (SoH-LED) are monolithically integrated with the AlGaN/GaN high-electron-mobility transistors (HEMT) on an AlGaN/GaN-on-Si platform commonly used for GaN lateral electronic devices. The on-chip electro-optic modulation is realized in a single device fabricated using HEMT-compatible process. Also, SoH-LED arrays are fabricated to demonstrate the on-chip addressable functionality with each SoH-LED pixel in the array individually controlled by the integrated HEMT. High-resolution micro-scale SoH-LED seven-segment displays are demonstrated to show the potential of using SoH-LEDs as a robust alternative for micro flat-panel displays. [ABSTRACT FROM AUTHOR]

In this work, by using an on-chip integrated Schottky-on-heterojunction light-emitting diode (SoHLED) which is seamlessly integrated with the AlGaN/GaN high electron mobility transistor (HEMT), we studied the effect of on-chip light illumination on the de-trapping processes of electrons from both surface and bulk traps. Surface trapping was generated by applying OFF-state drain bias stress, while bulk trapping was generated by applying positive substrate bias stress. The detrapping processes of surface and/or bulk traps were monitored by measuring the recovery of dynamic on-resistance Ron and/or threshold voltage Vth of the HEMT. The results show that the recovery processes of both dynamic Ron and threshold voltage Vth of the HEMT can be accelerated by the on-chip SoH-LED light illumination, demonstrating the potentiality of on-chip hybrid opto-HEMTs to minimize the influences of traps during dynamic operation of AlGaN/GaN power HEMTs. [ABSTRACT FROM AUTHOR]

Metamorphic InAs/In0.15Ga0.85As and InAs/In0.31Ga0.69As quantum dot (QD) arrays are known to be photosensitive in the telecommunication ranges at 1.3 and 1.55 μm, respectively; however, for photonic applications of these nanostructures, the effect of levels related to defects still needs in-depth investigation. We have focused on the influence of electron traps of defects on photocurrent (PC) in the plane of the QD array, studying by PC and deep level thermally stimulated current spectroscopy together with HRTEM and theoretical modeling. In the structures, a rich spectrum of electron trap levels of point defects EL6 (Ec − 0.37 eV), EL7 (0.29–0.30 eV), EL8 (0.27 eV), EL9/M2 (0.22–0.23 eV), EL10/M1 (0.16 eV), M0 (∼0.11 eV) and three extended defects ED1/EL3 (0.52–0.54), ED2/EL4 (0.47–0.48 eV), ED3/EL5 (0.42–0.43 eV) has been identified. Among them, new defect levels undiscovered earlier in InAs/InGaAs nanostructures has been detected, in particular, EL8 and M0. The found electron traps are shown to affect a time-dependent PC at low temperatures. Besides a long-term kinetics due to trap charging, a prolonged PC decrement versus time is measured under constant illumination. The decrement is interpreted to be related to a Coulomb screening of the conductivity channel by the electrons captured in the QD interface traps. The decrement is well fitted by allometric exponents, which means many types of traps involved in electron capturing. This study provides new findings into the mechanism of in-plane PC of QD arrays, showing a crucial importance of growth-related defects on photoresponsivity at low temperatures. [ABSTRACT FROM AUTHOR]

Metamorphic InAs/InGaAs quantum dot (QD) structures have been successfully used in optoelectronics as light-emitting and sensing devices. Previous optical and photoelectrical studies showed many benefits such as the shift of the operating range in the infrared and the possibility of engineering their properties via the control of strain. However, photovoltage (PV) kinetic properties of metamorphic QD structures have not been studied yet. PV kinetics in the vertical metamorphic InAs/In0.15Ga0.85As QD and wetting layer (WL) structures compared with conventional pseudomorphic InAs/GaAs QD ones are investigated. A red-shift of the photoresponse from metamorphic QDs in comparison with pseudomorphic QDs was observed, while the PV magnitudes remain similar. Moreover, time-dependent PV measurements reveal faster increase and decay rates in both the metamorphic samples. At the same time, all the structures reveal a non-monotonous kinetics. This kinetics is explained by an unwanted PV component generated in the interface of n+-GaAs buffer to the semi-insulating GaAs substrate, causing a signal opposite to the main PV generated at the top layers of structure. We believe the findings on faster carrier kinetics in metamorphic QDs can be helpful for the development of novel efficient optoelectronic devices. Specifically, the design of metamorphic QD structure is proposed to be improved by: (i) minimizing strain-related defects, (ii) keeping such interface defects far from QDs, (iii) utilizing n+-GaAs substrates. [ABSTRACT FROM AUTHOR]

We investigated the threshold voltage (VTH) shift in p-GaN gate AlGaN/GaN power HEMTs under both forward and reverse gate bias conditions at different temperatures. With increasing forward gate bias, the VTH first positively shifted and then decreased. While at the reverse gate bias, VTH shifts monotonically increased towards the positive direction. Positive VTH shifts were due to electron trapping while its decrease was attributed to the optical pumping by the internal electroluminescence (EL). The EL emission from the p-GaN gate region was captured. A light illumination test was performed to verify the effectiveness of optical pumping. [ABSTRACT FROM AUTHOR]

An increase in OFF-state leakage current in p-GaN gate AlGaN/GaN high-electron-mobility transistors (HEMTs), induced by ON-state gate bias, was observed and reported in this paper. Higher OFF-state leakage current was observed with higher gate bias voltage and longer bias duration. We propose that the initial increase in OFF-state leakage current and its subsequent decay with time are due to persistent photoconductivity effects in GaN induced by hole injection and electroluminescence during the ON-state gate bias. At room temperature, it took more than 20 s for the increased leakage current to reduce to its equilibrium level in the dark. The related physical mechanisms underlying this phenomenon in the p-GaN gate HEMT structure are also proposed. [ABSTRACT FROM AUTHOR]

The photocurrent characteristics of metal–AlGaN/GaN Schottky-on-heterojunction diodes were investigated. When the photon energy of incident light was larger than the bandgap of GaN but smaller than that of AlGaN, the alternating-current (ac) photocurrent measured using lock-in techniques increased with the chopper frequency. Analyzing the generation and flow processes of photocarriers revealed that the photocurrent induced by GaN interband excitation featured a transient behavior, and its direction reversed when the light excitation was removed. The abnormal dependence of the measured ac photocurrent magnitude on the chopper frequency was explained considering the detection principles of a lock-in amplifier. [ABSTRACT FROM AUTHOR]