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AlN/amorphous Ga2O3 heterojunction photodetectors were fabricated to achieve solar-blind UV detection. The responsivity and detectivity of the photodetector on a native substrate are 150% and 21.8% higher than those on a heterogeneous substrate at a 20 V bias, reaching 8.31 A W−1 and 3.24 × 1014 Jones, respectively. The built-in electric field enables self-powered UV detection without an external power supply. The addition of a nanocolumnar AlN structure significantly improved the performance of the photodetector, achieving a photo-to-dark current ratio and responsivity up to 2.11 × 107 and 9.17 mA W−1 at 0 V bias. The fabricated photodetector has demonstrated self-powered and high-sensitivity UV detection. [ABSTRACT FROM AUTHOR]

In this work, we fabricated a Van der Waals heterostructure of monolayer (ML) WS2 and InGaN quantum dots (QDs). This heterostructure is divided into coupled and uncoupled regions based on the thickness of the inserted hBN layer. Upon measuring its PL spectra, we identified an interfacial negative biexciton, which consists of a trion in ML WS2 and an exciton in QDs, in the coupled region. This interfacial negative biexciton features the negative charge of the trion and the quantum confinement of QDs, with its relative intensity showing a strong dependence on the excitation photon energy and featuring a significant threshold. Our work highlights the effective coupling within the mixed-dimensional heterostructure, offering new prospects for the study of many-body physics. [ABSTRACT FROM AUTHOR]

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 FROM AUTHOR]

High-quality aluminum nitride (AlN) crystals are the key material for the development of high-performance solid-state solar-blind vacuum-ultraviolet (VUV) photodetectors. However, the commonly used epitaxial method to grow AlN crystals would limit this development due to the existence of indispensable substrates. This study addresses this issue using free-standing lamellar AlN single crystals that are grown using the physical vapor transport method. The large lateral dimension of the crystal enables the construction of an Au-AlN-graphene van der Waals heterojunction, which can function as a vertical VUV photodetector with the graphene serving as the light window. The asymmetric junctions formed on the two sides of the crystal and the limited penetration of the VUV endow the device with a bias polarity-dependent photoresponse feature arising from different photoelectric processes. Furthermore, the device demonstrates a high responsivity of 5.77 A W−1 and a high specific detectivity of 1.71 × 1013 cm Hz1/2 W−1 under the illumination of a 193 nm laser. The high crystallinity of the AlN guarantees a high spectral selectivity of responsivity with a 193 nm/280 nm rejection ratio of 3 × 102. This work would inspire the development of wide-bandgap-semiconductor-based VUV photodetectors in terms of methodology and mechanism. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Visible-blind ultraviolet-selective photodetection and ultraviolet-visible broad spectral photodetection are two essential functions eagerly pursued in each application area. However, they usually cannot be realized simultaneously in a bare photodetector because their different underlying photoexcitation processes would interfere with each other. In this work, a photodetector integrating the two distinct photodetector characteristics is presented. The device is prepared based on the heterojunction of a large-scale aluminum nitride bulk crystal and monolayer graphene. The visible-blind ultraviolet-selective photodetection and the ultraviolet-visible broad spectral photodetection are separately manifested in the device depending on the bias polarity. Under a negative bias, the device is a visible-blind deep-ultraviolet photodetector, demonstrating a 193/785 nm rejection ratio of over 106 for the photocurrent and a 193/405 nm rejection ratio of over 103 for the signal/noise ratio. Under a positive bias, the device performs as a broad spectral photodetector responding to light from 193 to 785 nm. Systematical characterization reveals that different photodetection manners are the synergistical results of the different photon energies of the incident light, wavelength-dependent penetration depths in AlN, and the different working modes of the device under different bias conditions. This work provides a particular dual-functional photodetector, which is of great significance in terms of both application and device physics. [ABSTRACT FROM AUTHOR]

In this article, the thermally induced threshold voltage (${V}_{\text{TH}}$) shift was investigated on two types of normally- OFF p-GaN gate high-electron-mobility transistors (HEMTs), featuring either an Ohmic-type or a Schottky-type gate. A positive ${V}_{\text{TH}}$ shift in a Schottky-type device and a negative ${V}_{\text{TH}}$ shift in an Ohmic-type device were observed at elevated temperatures. Temperature-dependent gate current–voltage (${I}-{V}$) and the transfer-length-method (TLM) analysis revealed that the bias condition across the p-GaN/AlGaN/GaN heterostructures was changed in both Schottky- and Ohmic-type devices as temperature increased. We propose that: 1) temperature-enhanced hole injection through thermionic emission which lowers the knee voltage of the Ohmic-metal/ p-GaN contact in Ohmic-type devices and 2) thermally enhanced gate current which enlarges the bias voltage across the Schottky-metal/p-GaN junction in Schottky-type devices, resulted in the observed ${V}_{\text{TH}}$ instability characteristics. The photoluminescence measurements were conducted to verify the thermally-enhanced ionization of magnesium dopants in the p-GaN and the corresponding instability issues. [ABSTRACT FROM AUTHOR]

An AlGaN/GaN metal-heterostructure-metal (MHM) ultraviolet (UV) photodetector employing lateral Schottky contacts was fabricated and characterized at different temperatures. As the temperature increased from 25 to 250 °C, the photoresponsivity of the MHM photodetector increased 3.5 times. This was attributed to the spontaneous-polarization-induced spatial separation of the photogenerated electrons and holes and the increased optical absorption at higher temperatures. Meanwhile, the decay time constant of the photocurrent became approximately three orders of magnitude smaller. With the enhanced photoresponsivity and the decreased response time constant, kilohertz optical switching of the MHM photodetector was recorded at 250 °C. The AlGaN/GaN MHM photodetector, sharing the same GaN-on-Si electronics platform, provides an applicable candidate for an all-GaN integrated UV sensing and amplifying system for high-temperature applications. [ABSTRACT FROM AUTHOR]

Two‐dimensional layered crystals have attracted great attention due to their unique properties and practical interests for the application in nano‐optoelectronics. This work theoretically studies the effect of intralayer interaction on the Raman scattering in MoS2xSe2(1 − x) layered alloy, in particular, the change of intensity and position of the in‐plane and out‐of‐plane mode bands as a function of the concentration of S or Se atoms. The theory of Raman scattering in the layered alloys is developed, where the Green's function method is used to obtain the Raman scattering intensity. The Raman intensity is a function of the concentration of S or Se atoms in the layers and also a function of the parameters of intralayer and interlayer interactions. The modeling and numerical calculations show that the Raman spectrum mostly depends on the parameter describing the intralayer interaction between the unit cells containing S or Se atoms in the layer. The spectrum exhibits the two‐mode character when the intralayer interaction is weak while conserves the one‐mode character when the intralayer interaction increases to be comparable with the wavenumber position of the bands. The developed microscopic theoretical approach is versatile and can also be applied to interpret Raman spectra and explain some of their features in bulk and two‐dimensional layered alloys. [ABSTRACT FROM AUTHOR]

In this work, we demonstrated that ${p}$ -type and ${n}$ -type conduction could be induced in unintentionally doped pristine monolayer (ML) WS2 by forming a hybrid WS2/InGaN quantum dots (QDs) heterostructure, in which the ML-WS2 is partially covered by few-layer graphene. Under illumination, the photo-generated holes or electrons in the QDs were injected vertically into the ML-WS2 and then transported laterally therein. The polarity of the WS2 channel can be controlled by the bias applied to the graphene electrode. This work provides a potential approach to develop ambipolar devices of ML transition metal dichalcogenides through photocarrier doping. [ABSTRACT FROM AUTHOR]

Metamorphic InAs/InGaAs quantum dots (QDs) have been proposed as active elements for optoelectronic light-emitting devices operating in the infrared range. However, advanced structure design to allow efficient and stable enhancement of quantum yield at room temperature are still needed. Here, we compare a metamorphic InAs/In0.15Ga0.85As QD heterostructure with and without GaAs confining barriers, to investigate the effect of introducing GaAs barriers on the photo- and thermo-electrical properties. GaAs confining barriers allow to enhance the QD photoluminescence intensity at 1.3 µm, i.e. second telecommunication window, by more than two orders of magnitude at room temperature and at 80 K. We also discuss the effect of GaAs barriers on the carrier transport and on defect-related levels detected by means of photocurrent and deep level thermally stimulated current spectroscopies. GaAs confining barriers decrease the thermal escape rate of electrons confined in QD and wetting layer, thereby highly increasing the radiative recombination and also quenching the photocurrent. At low temperatures, the barriers also reduce the capture of electrons generated in InGaAs by the QD layer and, on the other hand, prevent the trapping of electrons outside the QD layer, decreasing carrier lifetimes. The deep levels identified as point and extended defects have been detected in the InGaAs layers. There are no new types of defects introduced in the structure by the addition of the barriers, but this causes a weakly increased density of traps near QDs. Our results show that InAs/InGaAs QDs with GaAs confining barriers can be efficient light emitters with only a slight increase of defects in the structure. Hence, such advanced design for metamorphic QDs can be of relevant interest for applications in energy-efficient QD lasers, optical amplifiers and single-photon emitters operating at 1.3–1.55 µm. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this work, the breakdown characteristics and the electroluminescence (EL) spectra of a Schottky-metal/p-GaN/AlGaN/GaN device under forward bias were investigated at different temperatures. The failure of the metal/p-GaN junction, which was caused by electron transport in the p-type Schottky junction, was identified as the first step in the device breakdown process. The breakdown voltage increased with higher temperatures. Under a forward bias of 8 V, the intensity of the EL emission increased more than two orders of magnitude, while the current increased by a factor of 4 as the temperature increased from 0 °C to 200 °C. This unambiguously demonstrated thermally enhanced hole injection at the Schottky-metal/p-GaN interface. We proposed that more electrons were annihilated by the thermally enhanced hole injection, resulting in the positive temperature dependence of the device breakdown. [ABSTRACT FROM AUTHOR]

Infrared photodetectors with In(Ga)As quantum dot (QD) active element functioning on interband and intersubband transitions are currently actively investigated, however, the vertical sensors were mostly reported. In the current study, a multilayer In0.4Ga0.6As/GaAs QD photodetector structure allowing the lateral photocurrent detection at normal incidence has been prepared depositing top contact. In order to have a comparison, a heterostructure with only a stack of In0.4Ga0.6As/GaAs wetting layers (WL) has been grown. In-depth photoelectrical characterization shows an effective broad-band photodetection related to the interband transitions between quantum-confined levels in QDs ranging from 1.03 to 1.38 eV (0.9–1.2 μm) that covers much wider infrared range in comparison to that from WLs (1.27–1.38 eV). Photoluminescence spectroscopy confirms the existence of QD transitions, observed as intense QD emission which peaked at 1.12 eV (∼1 μm) redshifted in comparison to the WL structure. The mechanisms of photoconductivity are modelled and discussed, comparing both the structures. We also show that our QD stack has an order lower contribution from defects compared to similar QD structures investigated before. At the same time, our structures demonstrate appropriate device characteristics at room temperature, such as the wide dynamic range from 10–2 to 103μW cm−2 and a high photoresponsivity up to 20 A W−1 at low excitation intensities over 10–2–10–1μW cm−2, while at higher excitation intensities the responsivity is reduced, exhibiting a strong spectral dependence. Thereby, our results show that the grown multilayer In0.4Ga0.6As/GaAs QD heterostructure is of relevant interest for application in lateral QD photodetectors. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this letter, we investigated the electroluminescence (EL) spectra and photovoltage spectrum of a Schottky-metal/ ${p}$ -GaN/AlGaN/GaN diode with a semitransparent anode electrode. By analyzing the bias-dependence of the EL spectra of the diode as well as the gate stress bias-/time- dependences of the threshold voltage shift of a ${p}$ -GaN gate HEMT, the electron/hole injection sequence, electron trapping, hole-assisted de-trapping, and optical pumping processes in the ${p}$ -GaN gate region are identified. The band diagrams of the Schottky-metal/ ${p}$ -GaN/AlGaN/GaN heterostructure under different forward bias voltages are proposed. [ABSTRACT FROM AUTHOR]

A new superjunction MOSFET (SJ-MOSFET) architecture with dual built-in Schottky diodes is proposed and studied with the numerical TCAD simulations. This letter is based on silicon. One Schottky contact is formed at the top of the n-pillar, while the other is formed at the bottom of the p-pillar. During the reverse conduction period, the Schottky junctions turn on at a lower voltage than the PN junction. The current flows through n-pillar and p-pillar in parallel, so the potential difference across the PN junction is kept below its turn-on voltage. Thus, minority carrier injection through the PN junction is completely suppressed, leading to a superior reverse recovery performance. Integration of a single Schottky contact to either the n-pillar or the p-pillar cannot completely suppress the turn-on of the PN junction in the SJ-MOSFET due to the potential drop created by the current through only one type of the pillars. Furthermore, the proposed dual-Schottky SJ-MOSFET reduces the gate charge (${Q} _{\mathrm {G}}$) and the gate-to-drain charge (${Q} _{\mathrm {GD}}$), compared with the conventional SJ-MOSFET, leading to better figures of merit. [ABSTRACT FROM AUTHOR]

Defect mediated nonradiative recombination limits the photoluminescence (PL) quantum yield of transition metal dichalcogenide monolayers (MLs). In this work, the enhancement of the PL intensity of ML WS2 is reported in a van der Waals heterostructure of WS2 ML and InGaN quantum dots (QDs) under excitation with photon energy larger than the bandgaps of both WS2 and QDs. The mechanism of this PL enhancement is due to the aggregation of excitons in WS2 ML toward the QD sites to form an interfacial bound state, which effectively mitigates the influence of defects. This exciton aggregation induced enhancement of PL intensity is more pronounced at low temperatures and under low power excitations. The lifetime and diffusion coefficient of the excitons in WS2 ML are also measured to validate the aggregation scenario. [ABSTRACT FROM AUTHOR]

Defect mediated nonradiative recombination limits the photoluminescence (PL) quantum yield of transition metal dichalcogenide monolayers (MLs). In this work, the enhancement of the PL intensity of ML WS2 is reported in a van der Waals heterostructure of WS2 ML and InGaN quantum dots (QDs) under excitation with photon energy larger than the bandgaps of both WS2 and QDs. The mechanism of this PL enhancement is due to the aggregation of excitons in WS2 ML toward the QD sites to form an interfacial bound state, which effectively mitigates the influence of defects. This exciton aggregation induced enhancement of PL intensity is more pronounced at low temperatures and under low power excitations. The lifetime and diffusion coefficient of the excitons in WS2 ML are also measured to validate the aggregation scenario. [ABSTRACT FROM AUTHOR]

A new silicon power MOSFET architecture is proposed by introducing a built-in channel diode through a dummy MOS gate electrically coupled to the source. The oxide thickness of the channel diode is reduced to obtain a desired turn-ON voltage and attenuate the minority carrier injection from the PN junction body diode. Consequently, the proposed MOSFET is able to deliver superior reverse recovery characteristics, including reductions in reverse recovery charge ($Q_{\sf RR}$) and peak reverse recovery current ($I_{\mathrm{ RRM}}$) by a factor of ~4.2 and ~2.6, respectively. The breakdown voltage (232 V) of the proposed MOSFET is the same as the conventional MOSFET. The on-resistance of the proposed MOSFET (8.5 $\text{m}\Omega \cdot \text {cm}^{{2}}$) is only slightly increased compared with conventional MOSFET (8.0 $\text{m}\Omega \cdot \text {cm}^{{2}}$). The gate-to-drain charge ($Q_{\sf GD}$) and gate charge (${Q} _{\mathsf {G}}$) are reduced by a factor of ~7.2 and ~3.9, respectively. Significantly improved figures of merit (${R} _{ON} \times {Q}_{\mathsf {G}}$ and ${R} _{ON} \times {Q}_{\mathsf {GD}}$ reduced by a factor of ~3.7 and ~6.8, respectively) are obtained in the proposed MOSFET. The device concept and characteristics are systematically analyzed with numerical TCAD simulations. [ABSTRACT FROM AUTHOR]

The gate structure of a ${p}$ -(Al)GaN gate AlGaN/GaN high electron mobility transistor (HEMT) is a direct bandgap hetero-PN junction, which emits light under forward bias above the threshold voltage. This internal light emission induces persistent photoconductivity (PPC) of the GaN channel/buffer layer, leading to the increase in OFF-state leakage current. In this letter, we studied the OFF-state leakage degradation induced by ON-state gate drive of a ${p}$ -GaN gate HEMT. Two self-limiting functions are discovered: 1) saturation of the increment of leakage current under continuous pulse operations and 2) dramatically enhanced recovery speed of the internal light-emission-induced PPC effect at elevated temperatures. This letter indicates the robustness of ${p}$ -(Al)GaN gate HEMTs in switching applications in spite of the seemingly inevitable leakage current degradation. [ABSTRACT FROM AUTHOR]

In this letter, we investigate the threshold voltage ( ${V}_{\text {TH}}$ ) shift in a p-GaN gate AlGaN/GaN transistor by designed gate-bias pulse measurements. It was found that the forward gate bias causes positive ${V}_{\text {TH}}$ shift. The dynamics of electron trapping was revealed from the dependences of the consequent ${V}_{\text {TH}}$ shift on the bias duration at different voltages. A time constant smaller than 0.1 ms for the ${V}_{\text {TH}}$ shift saturation at 6-V gate bias was obtained. It was also found that the ${V}_{\text {TH}}$ became inversely proportional to the gate-bias voltages exceeding 7 V. This inverse proportionality of the ${V}_{\text {TH}}$ shift resulted from the threshold of the hole-injection/electroluminescence (EL) and the sequential optical pumping effect on the electron traps. The EL emission was confirmed by a self- and in-situ photon detection measurement. [ABSTRACT FROM AUTHOR]

A systematic analytical investigation of the charge distribution and gate control of the normally-off GaN double-channel MOS-HEMT (DC-MOS-HEMT) is presented in this paper. Compared to conventional GaN MOS-HEMT, the DC-MOS-HEMT features a thin AlN insertion layer (AlN-ISL) below the original two dimensional electron gas (2DEG) channel, thus forming a second channel at the interface between AlN-ISL and the underlying GaN. This paper reveals the impact of the AlN-ISL on the 2DEG distribution and the gate control of the channels. The sensitivity of ${V}_{\text {th}}$ against the recess depth is also analytically studied and is found to be nearly independent of the recess depth as long as the recess is terminated in the upper channel layer. The analytical results are well supported by numerical device simulations, and the physical mechanisms behind these findings are explained along with the analytical investigations. [ABSTRACT FROM AUTHOR]