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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.

Semiconductor Cu2ZnSn(S x Se1-x )4 (CZTSSe) solid solution is considered as a perspective absorber material for solar cells. However, during its synthesis or deposition, any modification in the resulting optical properties is hardly predicted. In this study, experimental and theoretical analyses of CZTSSe bulk crystals and thin films are presented based on Raman scattering and absorption spectroscopies together with compositional and morphological characterizations. CZTSSe bulk and thin films are studied upon a change in the x = S/(S + Se) aspect ratio. The morphological study is focused on surface visualization of the solid solutions, depending on x variation. It has been discovered for the first time that the surface of the bulk CZTSSe crystal with x = 0.35 has pyramid-like structures. The information obtained from the elemental analysis helps to consider the formation of a set of possible intrinsic lattice defects, including vacancies, self-interstitials, antisites, and defect complexes. Due to these results and the experimentally obtained values of the band gap within 1.0-1.37 eV, a deviation from the calculated band gap values is estimated in the range of 1.0-1.5 eV. It is suggested which defects can have an influence on such a band gap change. Also, on comparing the experimental Raman spectra of CZTSSe with the theoretical modeling results, an excellent agreement is obtained for the main Raman bands. The proposed theoretical approach allows to estimate the values of concentration of atoms (S or Se) for CZTSSe solid solution directly from the experimental Raman spectra. Thus, the visualization of morphology and the proposed theoretical approach at various x values will help for a deeper understanding of the CZTSSe structure to develop next-generation solar cells.

Monolayer transition metal dichalcogenides (ML-TMDCs) are a versatile platform to explore the transport dynamics of the tightly bound excitonic states. The diffusion of neutral excitons in various ML-TMDCs has been observed. However, the transport of charged excitons (trions), which can be driven by an in-plane electric field and facilitate the formation of an excitonic current, has yet been well investigated. Here, we report the direct observation of diffusion and drift of the trions in ML-WS2 through spatially and time-resolved photoluminescence. An effective diffusion coefficient of 0.47 cm2/s was extracted from the broadening of spatial profiles of the trion emission. When an in-plane electric field is applied, the spatial shift of the trion emission profiles indicated a drift velocity of 7400 cm/s. Both the diffusion caused broadening and the drift caused shift of the emission profiles saturate because of the Coulomb interactions between trions and the background charges.

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.

The metal nanoparticle size and shape impact the plasmonic enhancement of Raman and photoluminescence (PL) spectra of monolayer and few-layer MoS2 decorated with them. The plasmonic enhancement is investigated for Ag nanotriangles (NTs or nanoprisms) of different sizes in comparison to Ag nanospheres (NSs) at room temperature. After the decoration with Ag NTs, the intensity of both Raman modes of MoS2 increases up to 6.8 times. The u-PL spectra of bare MoS2 show the presence of the A and B exciton bands as well as of a weak trion component. After covering the flakes with 50 nm Ag NTs, the highest integrated PL enhancement factors are 2.9 and 2.1 under 532 and 405 nm excitations, respectively. The revealed shape effect is that Ag NTs provide much stronger Raman and exciton emission enhancement than Ag NSs, which is due to the generation of plasmonic hot spots near the sharp edges and tips of NTs. Another mechanism of enhancement is the plasmonic coupling between the neighboring Ag NTs that causes the generation of hot spots in the gap between NTs. The revealed size effect is a decrease of Raman and PL enhancement with an increase in size of Ag NTs or NSs, which is due to an increase in radiative damping of plasmon oscillation occurring with an increase in nanoparticle size. The important feature is a strong enhancement of the A-trion component after decorating MoS2 with Ag nanoparticles. The phenomenon may be explained by the surface-plasmon-mediated generation of hot electrons in Ag nanostructures, which then inject to MoS2 flakes. This work gives new fundamental insights into the physical mechanisms of light-matter coupling in hybrid twodimensional (2D) semiconductor/plasmonic nanoparticle structures, which are highly promising for next-generation optoelectronic and nanophotonic devices.

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.

Strain in two-dimensional (2D) materials has attracted particular attention because of the remarkable modification of electronic and optical properties. However, emergent electromechanical phenomena and hidden mechanisms, such as strain-superlattice-induced topological states or flexoelectricity under strain gradient, remain under debate. Here, using scanning photocurrent microscopy, we observe significant photocurrent enhancement in hybrid vertical junction devices made of strained few-layer graphene and InGaN quantum dots. Optoelectronic response and photoluminescence measurements demonstrate a possible mechanism closely tied to the flexoelectric effect in few-layer graphene, where the strain can induce a lateral built-in electric field and assist the separation of electron-hole pairs. Photocurrent mapping reveals an unprecedentedly ordered hexagonal network, suggesting the potential to create a superlattice by strain engineering. Our work provides insights into optoelectronic phenomena in the presence of strain and paves the way for practical applications associated with strained 2D materials.

Two-dimensional (2D) MoS2 possesses unique optical and electrical properties and has many practical applications in nano-optoelectronics. Raman spectroscopy allows readily identify monolayer of MoS2, but the unambiguous determination of the number of layers in a few-layer structure remains a challenging task. In this work, the modification of frequencies of the most intense bands arising from in-plane and out-of-plane vibrations in the spectra of mono- and few-layer MoS2 crystals is studied experimentally, using the Raman scattering technique, and systematically analyzed theoretically, considering the influence of the interlayer interaction as well as the anharmonic interactions within the layer. A good agreement between experimental spectra and theoretical simulations is demonstrated, which allows to estimate the thickness of few-layer MoS2 and also determine parameters of the interlayer and anharmonic interactions. Possible effects of Fermi resonance in 2D MoS2 and the corresponding frequency shift of fundamental modes are considered. The proposed theoretical approach can be used to analyze Raman spectra, estimate the interlayer interaction, anharmonism, and the number of layers for other 2D layered materials.

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.

A Cu2ZnSnS4 (CZTS) thin film deposited on Mo contact film using direct current magnetron sputtering and sulfurized is studied. The morphological and structural investigations are focused on the interface between the CZTS film and the back Mo layer. The film is shown to be polycrystalline with an average grain size of 0.8 µm and of a high conductivity of the grain boundaries. It is also characterized by a suitable elemental composition with a noncritical deviation from the stoichiometry across the film depth. This results in the optical bandgap of 1.48 eV, which is optimal for solar cell absorbers. Raman spectra show low FWHMs of two A-symmetry dominant bands for CZTS thin film, which confirms a high quality of the crystal structure over a large area. At the same time, ZnS secondary phase is found on the film surface, while MoS2 is detected in the depth using a resonant excitation. The Raman mapping shows a non-uniform distribution of MoS2 along the interface between the CZTS film and the back Mo layer.

Harvesting solar energy for artificial photosynthesis is an emerging field in alternative energy research. In this work, the photocatalytic properties of InX(X = S, Se)/transition metal disulfide (MoS2 and WS2) van der Waals heterostructures have been investigated. The calculation results indicate that these heterostructures exhibit improved photocatalytic performance over that of isolated InX or transition metal disulfide monolayers. The studied heterostructures all have type-II band alignment with holes and electrons located at the TMD and InX side, respectively. This facilitates the spatial separation of photogenerated carriers and improves the photocatalytic efficiency. The carrier mobility of the designed heterostructures can be boosted compared with the isolated monolayers, thus enhancing the carrier transport properties. Moreover, the strain-tuned heterostructures can prominently manipulate the light-harvesting capability especially from the visible light to infrared light range. Among the studied heterostructures, InSe/MoS2 with the suitable band edge positions, excellent transport properties and strain tolerance, and the lowest overpotential for oxygen evolution, stands out as the most promising candidate for photocatalytic applications. This work opens an avenue for the design of highly efficient heterostructure photocatalysts for solar-to-energy applications.

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.

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.

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.

The trench gate structure is widely employed in silicon IGBTs because of the injection-enhancement effect (IE-effect) that reduces the conduction loss. However, the conventional trench gate structure cannot readily be transferred to SiC IGBT, since it would suffer from a high oxide field that severely threatens the device reliability. In this paper, the gate structure design of SiC trench IGBT is investigated through comprehensive numerical TCAD simulations. The grounded p-shield trench gate is widely adopted for oxide protection in SiC MOSFET but it counteracts the IE-effect in the SiC trench IGBT by extracting holes, thus nullifying the purpose of a trench gate. The floating p-shield trench gate is much easier to be implemented and more area effective. It is found that the floating p-shield provides similar oxide protection in the SiC trench IGBT as the grounded p-shield does, while a strong IE-effect is maintained. The dynamic degradation caused by a floating p-shield, as observed in SiC trench MOSFET, is effectively suppressed in the SiC trench IGBT, owing to the injected holes from collector that compensates the negative charge storage in the floating p-shield. Therefore, the floating p-shield structure is a promising solution for realizing high-performance SiC trench IGBTs.

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.

Monolayer transition metal dichalcogenides (TMDCs) are an ideal platform for multi-carrier bound states, the excitons and trions of which have been well identified and investigated. However, the formation and identification of biexcitons with certain configurations are more complicated. Here, we report a strategy to generate the hole-trion bound state, i.e. excited-state biexcitons, in a graphene/WS2 van der Waals heterostructure, the formation of which is attributed to the charge transfer and exciton dissociation at the hetero-interface. The biexciton nature is confirmed by excitation-power dependent, helicity-resolved, and time-resolved photoluminescence measurements. This hole-trion bound state features a thermal activation energy of ∼32 meV, rendering a stable excited-state biexciton emission up to 330 K. Moreover, the emission behavior of the excited-state biexcitons can be tuned by modifying the charge transfer process at the hetero-interface via electrostatic gating. Our results will benefit to further understanding the complex multi-carrier interactions in 2D semiconductors and related heterostructures.

MoS2 two-dimensional quantum dots (2D-QDs) are one of the novel 2D materials. In this work, MoS2 2D-QDs were grown on SiO2/Si by chemical vapor deposition and their exciton and trion photoluminescence were studied in comparison to MoS2 flakes. The 2D-QDs have a round-like shape with the average lateral size of 40 nm and tri-layer structure. Both the structures show two photoluminescence bands associated to A and B excitons, but the reduction of lateral dimension in 2D-QDs causes a recognized emission blueshift attributed to the quantum confinement. At the same time, the A exciton band of 2D-QDs is asymmetric, being overlapped with the trion band. We supposed that nano-dimensioned lateral sizes create quantum confinement conditions when all the excited electrons are also weakly localized in the plane of 2D-QD and much more effectively bind with holes as an additional electron of trion. It should be emphasized that 2D-QD has emission efficiency 6 times higher compared to that from the flake, that also can be explained by the charge carrier localization. These new findings offer potential applications of 2D-QDs in nano-devices operating at room temperatures involving multicolor engineering and efficient modulation of optical properties by controlling the QD lateral sizes and thickness.

P-grid is a typical feature in power devices to block high off-state voltage. In power devices, the p-grid is routinely coupled to an external electrode with an Ohmic contact, but Schottky contact to the p-grid is also proposed/adopted for certain purposes. This work investigates the role of contact to p-grid in power devices based on the commonly adopted technology computer-aided design (TCAD) device simulations, with the silicon carbide (SiC) junction barrier Schottky (JBS) diode as a case study. The static characteristics of the JBS diode is independent of the nature of the contact to p-grid, including the forward voltage drop (VF) and the breakdown voltage (BV). However, during the switching process, a Schottky contact would cause storage of negative charges in the p-grid, which leads to an increased VF during switching operation. On the contrary, an Ohmic contact provides an effective discharging path for the stored negative charges in the p-grid, which eliminates the dynamic degradation issues. Therefore, the necessity of an Ohmic contact to p-grid in power devices is clarified.

Harvesting solar energy for artificial photosynthesis is an emerging field in alternative energy research. In this work, the photocatalytic properties of InX(X = S, Se)/transition metal disulfide (MoS

The application of conventional power metal-oxide-semiconductor field-effect transistor (MOSFET) is limited by the famous one-dimensional &ldquo, silicon limit&rdquo, (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.

In(Ga)As quantum dots (QDs) are used in photonic and electronic devices with novel functionalities [1, 2, 3, 4, 5], advanced energy-efficient ‘green’ communication systems with ultra-large bit rate such as energy-efficient lasers [6, 7] and QD optical amplifiers [1], solar cells [8, 9, 10], single-photon emitters [11, 12, 13].