Defects‑Rich Heterostructures Trigger Strong Polarization Coupling in Sulfides/Carbon Composites with Robust Electromagnetic Wave Absorption

Defects-rich heterointerfaces integrated with adjustable crystalline phases and atom vacancies,as well as veiled dielectric-responsive character,are instrumental in electromagnetic dissipation.Conventional methods,however,constrain their delicate constructions.Herein,an innovative alternative is proposed:carrageenan-assistant cations-regulated(CACR)strategy,which induces a series of sulfides nanoparticles rooted in situ on the surface of carbon matrix.This unique configuration originates from strategic vacancy formation energy of sulfides and strong sulfides-carbon support interaction,benefiting the delicate construction of defects-rich heterostructures in M_(x)S_(y)/carbon composites(M-CAs).Impressively,these generated sulfur vacancies are firstly found to strengthen electron accumulation/consumption ability at heterointerfaces and,simultaneously,induct local asymmetry of electronic structure to evoke large dipole moment,ultimately leading to polarization coupling,i.e.,defect-type interfacial polarization.Such“Janus effect”(Janus effect means versatility,as in the Greek two-headed Janus)of interfacial sulfur vacancies is intuitively confirmed by both theoretical and experimental investigations for the first time.Consequently,the sulfur vacancies-rich heterostructured Co/Ni-CAs displays broad absorption bandwidth of 6.76 GHz at only 1.8 mm,compared to sulfur vacancies-free CAs without any dielectric response.Harnessing defects-rich heterostructures,this one-pot CACR strategy may steer the design and development of advanced nanomaterials,boosting functionality across diverse application domains beyond electromagnetic response.

A review of the most recent progresses of state-of-art gallium oxide power devices

Until very recently, gallium oxide(Ga_2O_3) has aroused more and more interests in the area of power electronics due to its ultra-wide bandgap of 4.5–4.8 eV, estimated critical field of 8 MV/cm and decent intrinsic electron mobility limit of250 cm2/(V·s), yielding a high Baliga's figures-of-merit(FOM) of more than 3000, which is several times higher than GaN and SiC.In addition to its excellent material properties, potential low-cost and large size substrate through melt-grown methodology also endows β-Ga_2O_3 more potential for future low-cost power devices. This article focuses on reviewing the most recent advances ofβ-Ga_2O_3 based power devices. It will be starting with a brief introduction to the material properties of β-Ga_2O_3 and then the growth techniques of its native substrate, followed by the thin film epitaxial growth. The performance of state-of-art β-Ga_2O_3 devices, including diodes and FETs are fully discussed and compared. Finally, potential solutions to the challenges of β-Ga_2O_3 are also discussed and explored.

Optimizing the Performance of CsPbI3-Based Perovskite Solar Cells via Doping a ZnO Electron Transport Layer Coupled with Interface Engineering

Interface engineering has been regarded as an effective and noninvasive means to optimize the performance of perovskite solar cells(PSCs).Here,doping engineering of a ZnO electron transport layer(ETL)and CsPbI3/ZnO interface engineering via introduction of an interfacial layer are employed to improve the performances of CsPbI3-based PSCs.The results show that when introducing a TiO2 buffer layer while increasing the ZnO layer doping concentration,the open-circuit voltage,power conversion efficiency,and fill factor of the CsPbI3-based PSCs can be improved to 1.31 V,21.06%,and 74.07%,respectively,which are superior to those of PSCs only modified by the TiO2 buffer layer or high-concentration doping of ZnO layer.On the one hand,the buffer layer relieves the band bending and structural disorder of CsPbI3.On the other hand,the increased doping concentration of the ZnO layer improves the conductivity of the TiO2/ZnO bilayer ETL because of the strong interaction between the TiO2 and ZnO layers.However,such phenomena are not observed for those of a PCBM/ZnO bilayer ETL because of the weak interlayer interaction of the PCBM/ZnO interface.These results provide a comprehensive understanding of the CsPbI3/ZnO interface and suggest a guideline to design high-performance PSCs.

Recent Progress of Electrode Materials for Flexible Perovskite Solar Cells

Flexible perovskite solar cells(FPSCs) have attracted enormous interest in wearable and portable electronics due to their high power-per-weight and low cost. Flexible and efficient perovskite solar cells require the development of flexible electrodes compatible with the optoelectronic properties of perovskite. In this review, the recent progress of flexible electrodes used in FPSCs is comprehensively reviewed. The major features of flexible transparent electrodes, including transparent conductive oxides, conductive polymer, carbon nanomaterials and nanostructured metallic materials are systematically compared. And the corresponding modification strategies and device performance are summarized. Moreover, flexible opaque electrodes including metal films, opaque carbon materials and metal foils are critically assessed. Finally, the development directions and difficulties of flexible electrodes are given.

The electrical characteristics of a 4H-silicon carbide metal-insulator-semiconductor structure with Al_2O_3 as the gate dielectric

A 4H-silicon carbide metal-insulator-semiconductor structure with ultra-thin Al2O3 as the gate dielectric, deposited by atomic layer deposition on tile epitaxial layer of a 4H-SiC （0001） 80N-/N＋ substrate, has been fabricated. The experimental results indicate that the prepared ultra-thin Al2O3 gate dielectric exhibits good physical and electrical characteristics, including a high breakdown electrical field of 25 MV/cm, excellent interface properties （1 × 10^14 cm^-2） and low gate-leakage current （IG = 1 × 10^-3 A/cm 2@Eox = 8 MV/cm）. Analysis of the current conduction mecha- nism on the deposited Al2O3 gate dielectric was also systematically performed. The confirmed conduction mechanisms consisted of Fowler-Nordheim （FN） tuaneling, the Frenkel-Poole mechanism, direct tunneling and Schottky emission, and the dominant current conduction mechanism depends on the applied electrical field. When the gate leakage current mechanism is dominated by FN tunneling, the barrier height of SiC/Al2O3 is 1.4 eV, which can meet the requirements of silicon carbide metal-insulator-semiconductor transistor devices.

Improved mobility of AlGaN channel heterojunction material using an AlGaN/GaN composite buffer layer

The quality of an A1GaN channel heterojunction on a sapphire substrate is massively improved by using an A1- GaN/GaN composite buffer layer. We demonstrate an A10.4Gao.6N/AI0.18Ga0.82N heterojunction with a state-of-the-art mobility of 815 cm2/（V.s） and a sheet resistance of 890Ω/口 under room temperature. The crystalline quality and the electrical properties of the A1GaN heterojunction material are analyzed by atomic force microscopy, high-resolution X-ray diffraction, and van der Pauw Hall and capacitance-voltage （C-V） measurements. The results indicate that the improved electrical properties should derive from the reduced surface roughness and low dislocation density.

Influence of ^(60)Co gamma radiation on fluorine plasma treated enhancement-mode high-electron-mobility transistor

A1GaN/GaN depletion-mode high-electron-mobility transistor （D-HEMT） and fluorine （F） plasma treated enhancement-mode high-electron-mobility transistor （E-HEMT） are exposed to 60Co gamma radiation with a dose of 1.6 Mrad （Si）. No degradation is observed in the performance of D-HEMT. However, the maximum transeonductance of E-HEMT is increased after radiation. The 2DEG density and the mobility are calculated from the results of capacitance-voltage measurement. The electron mobility decreases after fluorine plasma treatment and recovers after radiation. Conductance measurements in a frequency range from 10 kHz to 1 MHz are used to characterize the trapping effects in the devices. A new type of trap is observed in the F plasma treated E-HEMT compared with the D-HEMT, but the density of the trap decreases by radiation. Fitting of Gp/w data yields the trap densities DT = （1-3）Х1012 cm^-2.eV^-1 and DT = （0,2-0.8）Х10^12 cm^2-eV^-1 before and after radiation, respectively. The time constant is 0.5 ms-6 ms. With F plasma treatment, the trap is introduced by etch damage and degrades the electronic mobility. After 60Co gamma radiation, the etch damage decreases and the electron mobility is improved. The gamma radiation can recover the etch damage caused by F plasma treatment.

Degradation of β-Ga_(2)O_(3) Schottky barrier diode under swift heavy ion irradiation

The electrical characteristics and microstructures ofβ-Ga_(2)O_(3) Schottky barrier diode(SBD)devices irradiated with swift heavy ions(2096 MeV Ta ions)have been studied.It was found thatβ-Ga_(2)O_(3) SBD devices showed the reliability degradation after irradiation,including turn-on voltage Von,on-resistance Ron,ideality factor n,and the reverse leakage current density Jr.In addition,the carrier concentration of the drift layer was decreased significantly and the calculated carrier removal rates were 5×10^(6)-1.3×10^(7)cm^(-1).Latent tracks induced by swift heavy ions were observed visually in the wholeβ-Ga2O3 matrix.Furthermore,crystal structure of tracks was amorphized completely.The latent tracks induced by Ta ions bombardments were found to be the reason for the decrease in carrier mobility and carrier concentration.Eventually,these defects caused the degradation of electrical characteristics of the devices.In terms of the carrier removal rates,theβ-Ga_(2)O_(3) SBD devices were more sensitive to swift heavy ions irradiation than SiC and GaN devices.

Investigation of AlGaN/GaN fluorine plasma treatment enhancement-mode high electronic mobility transistors by frequency-dependent capacitance and conductance analysis

This paper reports fluorine plasma treatment enhancement-mode HEMTs （high electronic mobility transistors） EHEMTs and conventional depletion-mode HEMTs DHEMTs fabricated on one wafer using separate litho-photography technology. It finds that fluorine plasma etches the AlGaN at a slow rate by capacitance-voltage measurement. Using capacitance-frequency measurement, it finds one type of trap in conventional DHEMTs with TT = （0.5 - 6） ms and DT ： （1 - 5）×10^13 cm^-2. eV^-1. Two types of trap are found in fluorine plasma treatment EHEMTs, fast with TW（f）= （0.2 - 2） μs and slow with TT（s） = （0.5 - 6） ms. The density of trap states evaluated on the EHEMTs is Dw（f） ： （1 - 3） × 10^12 cm^-2. eV^-1 and DT（s） =（2 - 6） × 10^12 cm-2. eV-1 for the fast and slow traps, respectively. The result shows that the fluorine plasma treatment reduces the slow trap density by about one order, but introduces a new type of fast trap. The slow trap is suggested to be a surface trap, related to the gate leakage current.

Fabrications and characterizations of high performance 1.2 kV,3.3 kV, and 5.0 kV class 4H–SiC power SBDs

In this paper, 1.2 kV, 3.3 kV, and 5.0 kV class 4H-SiC power Schottky barrier diodes （SBDs） are fabricated with three N-type drift layer thickness values of 10 μm, 30μm, and 50 μm, respectively. The avalanche breakdown capabilities, static and transient characteristics of the fabricated devices are measured in detail and compared with the theoretical pre- dictions. It is found that the experimental results match well with the theoretical calculation results and are very close to the 4H-SiC theoretical limit line. The best achieved breakdown voltages （BVs） of the diodes on the 10 p.m, 30 m, and 50 -tm epilayers are 1400 V, 3320 V, and 5200 V, respectively. Differential specific-on resistances （Ron-sp） are 2.1 m--cm2, 7.34 mO. cm2, and 30.3 m-. cm2, respectively.

Breakdown voltage analysis of Al_(0.25)Ga_(0.75)N/GaN high electron mobility transistors with partial silicon doping in the AlGaN layer

In this paper,two-dimensional electron gas（2DEG） regions in AlGaN/GaN high electron mobility transistors（HEMTs） are realized by doping partial silicon into the AlGaN layer for the first time.A new electric field peak is introduced along the interface between the AlGaN and GaN buffer by the electric field modulation effect due to partial silicon positive charge.The high electric field near the gate for the complete silicon doping structure is effectively decreased,which makes the surface electric field uniform.The high electric field peak near the drain results from the potential difference between the surface and the depletion regions.Simulated breakdown curves that are the same as the test results are obtained for the first time by introducing an acceptor-like trap into the N-type GaN buffer.The proposed structure with partial silicon doping is better than the structure with complete silicon doping and conventional structures with the electric field plate near the drain.The breakdown voltage is improved from 296 V for the conventional structure to 400 V for the proposed one resulting from the uniform surface electric field.

Thickness effect on solar-blind photoelectric properties of ultrathinβ-Ga_(2)O_(3)films prepared by atomic layer deposition

Theβ-Ga_(2)O_(3)films with different thicknesses are prepared by an atomic layer deposition system.The influence of film thickness on the crystal quality is obvious,indicating that the thicker films perform better crystal quality,which is verified from x-ray diffraction(XRD)and scanning electron microscope(SEM)results.The Ga_(2)O_(3)-based solar blind photodetectors with different thicknesses are fabricated and studied.The experimental results show that the responsivity of the photodetectors increases exponentially with the increase of the film thickness.The photodetectors with inter-fingered structure based on 900 growth cyclesβ-Ga_(2)O_(3)active layers(corresponding film thickness of 58 nm)exhibit the best performances including a low dark current of 134 fA,photo-to-dark current ratio of 1.5×10^(7),photoresponsivity of 1.56 A/W,detectivity of 2.77×10^(14)Jones,and external quantum efficiency of 764.49%at a bias voltage of 10 V under 254-nm DUV illumination.The photoresponse rejection ratio(R_(254)/R_(365))is up to 1.86×10^(5).In addition,we find that the photoelectric characteristics also depend on the finger spacing of the MSM structure.As the finger spacing decreases from 50μm to10μW,the photoresponsivity,detectivity,and external quantum efficiency increase significantly.

Fully Printed High‑Performance n‑Type Metal Oxide Thin‑Film Transistors Utilizing Coffee‑Ring Effect

Metal oxide thin-films transistors(TFTs)produced from solution-based printing techniques can lead to large-area electronics with low cost.However,the performance of current printed devices is inferior to those from vacuum-based methods due to poor film uniformity induced by the“coffeering”effect.Here,we report a novel approach to print highperformance indium tin oxide(ITO)-based TFTs and logic inverters by taking advantage of such notorious effect.ITO has high electrical conductivity and is generally used as an electrode material.However,by reducing the film thickness down to nanometers scale,the carrier concentration of ITO can be effectively reduced to enable new applications as active channels in transistors.The ultrathin(~10-nm-thick)ITO film in the center of the coffee-ring worked as semiconducting channels,while the thick ITO ridges(>18-nm-thick)served as the contact electrodes.The fully inkjet-printed ITO TFTs exhibited a high saturation mobility of 34.9 cm2 V^(−1) s^(−1) and a low subthreshold swing of 105 mV dec^(−1).In addition,the devices exhibited excellent electrical stability under positive bias illumination stress(PBIS,ΔV_(th)=0.31 V)and negative bias illuminaiton stress(NBIS,ΔV_(th)=−0.29 V)after 10,000 s voltage bias tests.More remarkably,fully printed n-type metal–oxide–semiconductor(NMOS)inverter based on ITO TFTs exhibited an extremely high gain of 181 at a low-supply voltage of 3 V,promising for advanced electronics applications.

Demonstration of a 4H SiC Betavoltaic Nuclear Battery Based on Scbottky Barrier Diode

A 4H SiC betavoltaic nuclear battery is demonstrated. A Schottky barrier diode is utilized for carrier separation. Under illumination of Ni-63 source with an apparent activity of 4mCi/cm^2, an open circuit voltage of 0.49 V and a short circuit current density of 29.44nA/cm^2 are measured. A power conversion efficiency of 1.2% is obtained. The performance of the device is limited by low shunt resistance, backscattering and attenuation of electron energy in air and Schottky electrode. It is expected to be significantly improved by optimizing the design and processing technology of the device.

Effect of NO annealing on charge traps in oxide insulator and transition layer for 4H-SiC metal–oxide–semiconductor devices

The effect of nitric oxide（NO） annealing on charge traps in the oxide insulator and transition layer in n-type4H–Si C metal–oxide–semiconductor（MOS） devices has been investigated using the time-dependent bias stress（TDBS）,capacitance–voltage（C–V）,and secondary ion mass spectroscopy（SIMS）.It is revealed that two main categories of charge traps,near interface oxide traps（Nniot） and oxide traps（Not）,have different responses to the TDBS and C–V characteristics in NO-annealed and Ar-annealed samples.The Nniotare mainly responsible for the hysteresis occurring in the bidirectional C–V characteristics,which are very close to the semiconductor interface and can readily exchange charges with the inner semiconductor.However,Not is mainly responsible for the TDBS induced C–V shifts.Electrons tunneling into the Not are hardly released quickly when suffering TDBS,resulting in the problem of the threshold voltage stability.Compared with the Ar-annealed sample,Nniotcan be significantly suppressed by the NO annealing,but there is little improvement of Not.SIMS results demonstrate that the Nniotare distributed within the transition layer,which correlated with the existence of the excess silicon.During the NO annealing process,the excess Si atoms incorporate into nitrogen in the transition layer,allowing better relaxation of the interface strain and effectively reducing the width of the transition layer and the density of Nniot.

Influence of Triangle Structure Defect on the Carrier Lifetime of the 4H-SiC Ultra-Thick Epilayer

Effect of triangle structure defects in a 180-μm-thick as-grown n-type 4H-SiC homoepitaxial layer on the carrier lifetime is quantitatively analyzed, which is grown by a horizontal hot-wall chemical vapor deposition reactor.By microwave photoconductivity decay lifetime measurements and photoluminescence measurements, the results show that the average carrier lifetime of as-grown epilayer across the whole wafer is 2.59μs, while it is no more than 1.34μs near a triangle defect（TD）. The scanning transmission electron microscope results show that the triangle structure defects have originated from 3C-SiC polytype and various types of as-grown stacking faults.Compared with the as-grown stacking faults, the 3C-SiC polytype has a great impact on the lifetime. The reduction of TD is essential to increasing the carrier lifetime of the as-grown thick epilayer.

Double superlattice structure for improving the performance of ultraviolet light-emitting diodes

The novel AlGaN-based ultraviolet light-emitting diodes(UV-LEDs) with double superlattice structure(DSL) are proposed and demonstrated by numerical simulation and experimental verification. The DSL consists of 30-period Mg modulation-doped p-AlGaN/u-GaN superlattice(SL) and 4-period p-AlGaN/p-GaN SL electron blocking layer, which are used to replace the p-type GaN layer and electron blocking layer of conventional UV-LEDs, respectively. Due to the special effects and interfacial stress, the AlGaN/GaN short-period superlattice can reduce the acceptor ionization energy of the ptype regions, thereby increasing the hole concentration. Meanwhile, the multi-barrier electron blocking layers are effective in suppressing electron leakage and improving hole injection. Experimental results show that the enhancements of 22.5%and 37.9% in the output power and external quantum efficiency at 120 m A appear in the device with double superlattice structure.

Photoresponse and trap characteristics of transparent AZO-gated AlGaN/GaN HEMT

AZO-gated and Ni/Au-gated AlGaN/GaN HEMTs are fabricated successfully,and an excellent transparency of AZOgated electrode is achieved.After a negative gate bias stress acts on two kinds of the devices,their photoresponse characteristics are investigated by using laser sources with different wavelengths.The effect of photoresponse on AZO-gated electrode device is more obvious than on Ni/Au-gated electrodes device.The electrons are trapped in the AlGaN barrier of AZO-gated HEMT after it has experienced negative gate bias stress,and then the electrons can be excited effectively after it has been illuminated by the light with certain wavelengths.Furthermore,the trap state density DTand the time constantτTof the AZO-gated Schottky contact are extracted by fitting the measured parallel conductance in a frequency range from10 kHz to 10 MHz.The constants of the trap range from about 0.35 μs to 20.35 μs,and the trap state density increased from1.93×l013eV 1·cm~2 at an energy of 0.33 eV to 3.07×1011eV~1·cm~2 at an energy of 0.40 eV.Moreover,the capacitance and conductance measurements are used to characterize the trapping effects under different illumination conditions in AZO-gated HEMTs.Reduced deep trap states’ density is confirmed under the illumination of short wavelength light.

Effects of growth temperature and metamorphic buffer on electron mobility of InAs film grown on Si substrate by molecular beam epitaxy

The growth of the InAs film directly on the Si substrate deflected from the plane(100) at 4° towards(110) has been performed using a two-step procedure. The effect of the growth and annealing temperature on the electron mobility and surface topography has been investigated for a set of samples. The results show that the highest electron mobility is4640 cm^2/V·s in the sample, in which the 10-nm InAs nucleation layer is grown at a low temperature of 320 ℃ followed by ramping up to 560 ℃, and the nucleation layer was annealed for 15 min and the second layer of InAs is grown at 520 ℃.The influence of different buffer layers on the electron mobility of the samples has also been investigated, which shows that the highest electron mobility of 9222 cm^2/V·s at 300 K is obtained in the sample grown on a thick and linearly graded InGaAlAs metamorphic buffer layer deposited at 420 ℃.

Improved crystal quality of GaN film with the in-plane lattice-matched In_(0.17)Al_(0.83)N interlayer grown on sapphire substrate using pulsed metal organic chemical vapor deposition

We report on an improvement in the crystal quality of GaN film with an Ino.17Alo.83N interlayer grown by pulsed metal-organic chemical vapor deposition, which is in-plane lattice-matched to GaN films. The indium composition of about 17% and the reductions of both screw and edge threading dislocations （TDs） in GaN film with the InA1N interlayer are estimated by high resolution X-ray diffraction. Transmission electron microscopy （TEM） measurements are employed to understand the mechanism of reduction in TD density. Raman and photoluminescence measurements indicate that the InA1N interlayer can improve the crystal quality of GaN film, and verify that there is no additional residual stress induced into the GaN film with InA1N interlayer. Atomic force microscopy measurement shows that the InA1N interlayer brings in a smooth surface morphology of GaN film. All the results show that the insertion of the InA1N interlayer is a convenient method to achieve excellent crystal quality in GaN epitaxy.