Recent progresses in thermal treatment of β-Ga_(2)O_(3) single crystals and devices

In recent years,ultra-wide bandgap β-Ga_(2)O_(3) has emerged as a fascinating semiconductor material due to its great potential in power and photoelectric devices.In semiconductor industrial,thermal treatment has been widely utilized as a convenient and effective approach for substrate property modulation and device fabrication.Thus,a thorough summary of β-Ga_(2)O_(3) substrates and devices behaviors after high-temperature treatment should be significant.In this review,we present the recent advances in modulating properties of β-Ga_(2)O_(3) substrates by thermal treatment,which include three major applications:(ⅰ)tuning surface electrical properties,(ⅱ)modifying surface morphology,and(ⅲ)oxidating films.Meanwhile,regulating electrical contacts and handling with radiation damage and ion implantation have also been discussed in device fabrication.In each category,universal annealing conditions were speculated to figure out the corresponding problems,and some unsolved questions were proposed clearly.This review could construct a systematic thermal treatment strategy for various purposes and applications of β-Ga_(2)O_(3).

Anisotropic etching mechanisms of 4H-SiC:Experimental and first-principles insights

Molten-alkali etching has been widely used to reveal dislocations in 4H silicon carbide(4H-SiC),which has promoted the identification and statistics of dislocation density in 4H-SiC single crystals.However,the etching mechanism of 4H-SiC is limited misunderstood.In this letter,we reveal the anisotropic etching mechanism of the Si face and C face of 4H-SiC by combining molten-KOH etching,X-ray photoelectron spectroscopy(XPS)and first-principles investigations.The activation energies for the molten-KOH etching of the C face and Si face of 4H-SiC are calculated to be 25.09 and 35.75 kcal/mol,respectively.The molten-KOH etching rate of the C face is higher than the Si face.Combining XPS analysis and first-principles calculations,we find that the molten-KOH etching of 4H-SiC is proceeded by the cycling of the oxidation of 4H-SiC by the dissolved oxygen and the removal of oxides by molten KOH.The faster etching rate of the C face is caused by the fact that the oxides on the C face are unstable,and easier to be removed with molten alkali,rather than the C face being easier to be oxidized.

Identification of subsurface damage of 4H-SiC wafers by combining photo-chemical etching and molten-alkali etching

In this work,we propose to reveal the subsurface damage(SSD)of 4H-SiC wafers by photo-chemical etching and identify the nature of SSD by molten-alkali etching.Under UV illumination,SSD acts as a photoluminescence-black defect.The selective photo-chemical etching reveals SSD as the ridge-like defect.It is found that the ridge-like SSD is still crystalline 4H-SiC with lattice distortion.The molten-KOH etching of the 4H-SiC wafer with ridge-like SSD transforms the ridge-like SSD into groove lines,which are typical features of scratches.This means that the underlying scratches under mechanical stress give rise to the formation of SSD in 4H-SiC wafers.SSD is incorporated into 4H-SiC wafers during the lapping,rather than the chemical mechanical polishing(CMP).

Discrimination of dislocations in 4H-SiC by inclination angles of molten-alkali etched pits

Discrimination of dislocations is critical to the statistics of dislocation densities in 4H silicon carbide(4H-SiC),which are routinely used to evaluate the quality of 4H-SiC single crystals and homoepitaxial layers.In this work,we show that the inclination angles of the etch pits of molten-alkali etched 4H-SiC can be adopted to discriminate threading screw dislocations(TSDs),threading edge dislocations(TEDs)and basal plane dislocations(BPDs)in 4H-SiC.In n-type 4H-SiC,the inclination angles of the etch pits of TSDs,TEDs and BPDs in molten-alkali etched 4H-SiC are in the ranges of 27°−35°,8°−15°and 2°−4°,respectively.In semi-insulating 4H-SiC,the inclination angles of the etch pits of TSDs and TEDs are in the ranges of 31°−34°and 21°−24°,respectively.The inclination angles of dislocation-related etch pits are independent of the etching duration,which facilitates the discrimination and statistic of dislocations in 4H-SiC.More significantly,the inclination angle of a threading mixed dislocations(TMDs)is found to consist of characteristic angles of both TEDs and TSDs.This enables to distinguish TMDs from TSDs in 4H-SiC.

Assessing the effect of hydrogen on the electronic properties of 4H-SiC

As a common impurity in 4 H silicon carbide(4 H-Si C),hydrogen(H)may play a role in tuning the electronic properties of 4 H-Si C.In this work,we systemically explore the effect of H on the electronic properties of both n-type and p-type4 H-Si C.The passivation of H on intrinsic defects such as carbon vacancies(V_(Si) )and silicon vacancies(V_(Si)) in 4 H-Si C is also evaluated.We find that interstitial H at the bonding center of the Si-C bond(H_(i)^(bc)) and interstitial H at the tetrahedral center of Si(H_(i)^(bc)) dominate the defect configurations of H in p-type and n-type 4 H-Si C,respectively.In n-type 4 H-Si C,the compensation of HSi-te iis found to pin the Fermi energy and hinder the increase of the electron concentration for highly N-doped 4 H-Si C.The compensation of Hbc iis negligible compared to that of V_(Si)on the p-type doping of Al-doped 4 H-Si C.We further examine whether H can passivate VCand improve the carrier lifetime in 4 H-Si C.It turns out that nonequilibrium passivation of VCby H is effective to eliminate the defect states of V_(Si),which enhances the carrier lifetime of moderately doped 4 H-Si C.Regarding the quantum-qubit applications of 4 H-Si C,we find that H can readily passivate V_(Si)during the creation of V_(Si)centers.Thermal annealing is needed to decompose the resulting V_(Si)-n H(n=1-4)complexes and promote the uniformity of the photoluminescence of V_(Si)arrays in 4 H-Si C.The current work may inspire the impurity engineering of H in 4 H-Si C.

Hyperdoped silicon:Processing,properties,and devices

Hyperdoping that introduces impurities with concentrations exceeding their equilibrium solubility has been attract-ing great interest since the tuning of semiconductor properties increasingly relies on extreme measures.In this review we fo-cus on hyperdoped silicon(Si)by introducing methods used for the hyperdoping of Si such as ion implantation and laser dop-ing,discussing the electrical and optical properties of hyperdoped bulk Si,Si nanocrystals,Si nanowires and Si films,and present-ing the use of hyperdoped Si for devices like infrared photodetectors and solar cells.The perspectives of the development of hy-perdoped Si are also provided.

Technoeconomically competitive four-terminal perovskite/graphenesilicon tandem solar cells with over 20% efficiency

Perovskite/Silicon(PS) tandem solar cells have attracted much interest over recent years. However, the most popular crystalline silicon solar cells utilized in tandems require complicated fabrication processes mainly including texturization, diffusion, passivation and metallization, which takes up much cost in photovoltaic market. Here, we report a facile graphene/silicon(Gr/Si) solar cell featuring of lowtemperature( 200 °C) processing and an efficiency of 13.56%. For reducing the heat dissipation loss of high energy photon, the perovskite solar cell(PSC) with a wide band gap of 1.76 e V was adopted as the top cell for the tandem. To reduce the loss of parasitic absorption in hole transport layers(HTLs),thickness of Spiro-OMe TAD is re-optimized by compromising the efficiency and the optical transmittance of the devices. As a result, the semitransparent top perovskite solar cell yields a highest efficiency of13.35%. Furthermore, we firstly achieved a low-temperature-processed four-terminal(4-T) perovskite/graphene-silicon(PGS) heterojunction tandem solar cell with the efficiency of 20.37%. The levelized cost of electricity(LCOE) of PGS 4-T modules were estimated to a competitive price, exhibiting much greater potential for practical application compared to that of PS 4-T modules.

Theoretical study on the improvement of the doping efficiency of Al in 4H-SiC by co-doping group-IVB elements

The p-type doping efficiency of 4 H silicon carbide(4 H-SiC)is rather low due to the large ionization energies of p-type dopants.Such an issue impedes the exploration of the full advantage of 4 H-SiC for semiconductor devices.In this study,we show that co-doping group-IVB elements effectively decreases the ionization energy of the most widely used p-type dopant,i.e.,aluminum(Al),through the defect-level repulsion between the energy levels of group-IVB elements and that of Al in 4 H-SiC.Among group-IVB elements Ti has the most prominent effectiveness.Ti decreases the ionization energy of Al by nearly 50%,leading to a value as low as~0.13 eV.As a result,the ionization rate of Al with Ti co-doping is up to~5 times larger than that without co-doping at room temperature when the doping concentration is up to 10^(18)cm^(-3).This work may encourage the experimental co-doping of group-IVB elements such as Ti and Al to significantly improve the p-type doping efficiency of 4 H-SiC.

A Novel Hydrothermal Synthesis of Single Crystalline PbS Nanorods and Their Characterization

Lead sulfide （PbS） nanorods with a high aspect ratio were prepared by a novel thioglycolic acid assisted hydrothermal method. X-ray diffraction and transmission electron microscopy revealed that the product was rod-like PbS with cubic rock-salt structure. Further characterizations by selected area electron diffraction and high-resolution transmission electron microscopy showed that the PbS nanorods were single crystalline in nature. Furthermore, the mechanism and critical factors for the hydrothermal synthesis of the nanorods have been discussed.

Ultrathin zirconium-porphyrin based nanobelts as photo-coupled electrocatalysis for CH_(4) oxidation to CO

The development of novel and effective methods for the activation of methane is fascinating,which offers a promising potential for the sustainable development of chemical industry and the mitigation of greenhouse effect.Here we successfully synthesize two-dimensional(2D)Zr/5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin(TCPP)ultrathin nanobelts(UNBs)as a high efficiency catalyst for methane(CH_(4))oxidation to carbon monoxide(CO).The Co-UNBs show well photo-coupled electrocatalytic performances for CH4 activation(CO production rates are 0.171 and 8.416 mmol·g−1·h−1 under dark/visible light,respectively).Density functional theory(DFT)calculations were performed to illustrate the mechanism of photoelectrocatalytic process and the high efficiency oxidation of CH4 to CO.Based on the ultrathin structure and highly efficient catalytic properties,this work provides a prospecting avenue for the design and synthesis of methane oxidation catalyst.

Detector-grade perovskite single-crystal wafers via stress-free gel-confined solution growth targeting high-resolution ionizing radiation

Solution-processed organic‒inorganic halide perovskite(OIHP)single crystals(SCs)have demonstrated great potential in ionizing radiation detection due to their outstanding charge transport properties and low-cost preparation.However,the energy resolution(ER)and stability of OIHP detectors still lag far behind those of melt-grown inorganic perovskite and commercial CdZnTe counterparts due to the absence of detector-grade high-quality OIHP SCs.Here,we reveal that the crystallinity and uniformity of OIHP SCs are drastically improved by relieving interfacial stress with a facial gel-confined solution growth strategy,thus enabling the direct preparation of large-area detector-grade SC wafers up to 4 cm with drastically suppressed electronic and ionic defects.The resultant radiation detectors show both a small dark current below 1 nA and excellent baseline stability of 4.0×10^(-8) nA cm^(-1) s^(-1) V^(-1),which are rarely realized in OIHP detectors.Consequently,a record high ER of 4.9% at 59.5 keV is achieved under a standard 241Am gamma-ray source with an ultralow operating bias of 5 V,representing the best gamma-ray spectroscopy performance among all solution-processed semiconductor radiation detectors ever reported.

PdPtBi networked nanowires derived from Pd nanosheets as efficient catalysts for ethanol oxidation

Direct ethanol fuel cells(DEFCs)have received increasing attention as one of the most promising energy conversion devices.However,developing catalysts with high activity,long durability and strong anti-poisoning ability for ethanol oxidation is still challenging.Here,using Pd nanosheets as sacrificial templates,we have successfully synthesized PdPtBi networked nanowires(NWs)to improve the activity and stability for ethanol oxidation reaction(EOR)due to the addition of Bi.Density functional theory(DFT)calculations demonstrated the downshift of d-band center of Pd,which is beneficial to suppress CO poisoning and boost reaction kinetics for EOR.Impressively,the PdPtBi networked NWs exhibited the highest activity(11.08 A·mg_(Pd+Pt)^(-1)and 92.52 mA·cm^(-2))with an enhancement of 4.4 and 17.5 times relative to those of Pd/C,respectively and best stability with a 47.2%left versus only a 5.8%left for Pd/C of mass activity after 3,600 s towards EOR.This work deepens the understanding of controllable preparation of networked NWs and provides an effective strategy to design advanced catalysts with high activity and stability.

Enhancement of sensitized photoluminescence of erbium chloride silicate through regulating annealing

Erbium chloride silicate(ECS)nanocrystals and Si nanocrystals(Si NCs)co-embedded in silica films were prepared.And the sensitized luminescence of ECS was realized through interparticle energy transfer(IPET)in solid matrix.We focus on the effect of annealing temperature on the film microstructure and sensitized luminescence.The samples annealed at 1100℃have a moderate level of energy transfer efficiency and total Er3+concentration capable of radiative recombination.At the same time,they also have high luminescence intensity of Si NCs.Therefore,the samples annealed at 1100℃have good sensitizing luminescence performance of ECS.The strong luminesce nce intensity of sensitizers Si NCs and adjacent crystalline ECS nanocrystals are the keys to achieve excellent IPET in the solid matrix.The results provide a basis for optimizing sensitized luminescence of erbium compounds by regulating annealing.

Development of robust perovskite single crystal radiation detectors with high spectral resolution through synergetic trap deactivation and self-healing

Organic-inorganic halide perovskite single crystals(SCs)are promising materials for detecting ionizing radiation owing to their outstanding photoelectric conversion capability and inexpensive solution processability.However,the accuracy and stability of the detectors have been limited due to the charge traps and defects in SCs,especially when operated under high-precision photon-counting mode for energy spectrum acquisition.Here,we proposed a trap freezing deactivation route,which obviously suppressed dark current and noise by up to 97%and 92%,respectively.Furthermore,the bulk ion migration effect was essential for the ability to instantly self-heal defects induced by radiation damage at temperatures down to30C.Consequently,the detector exhibits a record high energy resolution of 7.5%at 59.5 keV for 241Amγ-ray source,which is the best solution-processed semiconductor radiation detectors at the same energy range.In addition,the detector maintains over 90%of its initial performance after 9 months of storage when tested in the air.Our results will represent a revision of the paradigm that high-spectral-resolution and robust radiation detectors can only be realized with high temperature grown inorganic semiconductor single crystals.

光电神经突触器件研究进展

神经形态计算(类脑计算)以其自适应学习、高并行计算和低功耗等优点,被认为是最有希望解决冯·诺依曼(von Neumann)瓶颈的方法之一.实现神经形态计算的重要前提是开发能模拟生物突触行为的神经突触器件.电学神经突触器件是首先发展起来的神经突触器件,但是它们在统筹考虑带宽、连接、密度等因素下的整体优化面临着很大的挑战.近年来,把光引入神经突触器件,研制光电神经突触器件,为神经突触器件的发展带来了新机遇.对神经突触器件而言,光不仅具备电难以实现的高带宽、低串扰、低功率和无延迟等特性,还可以直接模拟视觉等至关重要的神经行为.光电神经突触器件作为基于光电集成的人工神经网络的基础,有望有力促进高性能和低功耗的神经形态计算的发展.本文主要介绍了光电神经突触器件的基本性能和类别,展示了已经实现的光电神经突触器件的模拟应用,并展望了今后光电神经突触器件的发展.

光/热耦合电催化活化二氧化碳和甲烷分子（英文）

新型催化方法的研究有助于实现二氧化碳和甲烷等小分子资源的高效利用,从而优化目前的碳循环工艺.二氧化碳和甲烷分子具有较高的键能,所以它们均为最稳定的分子之一.在过去十年,如何实现二氧化碳和甲烷分子的活化一直是世界难题.传统热催化通常使用化石燃料作为能源进行小分子活化,不仅效率低,同时会伴随着大量的二氧化碳生成.最近几年,一系列具有应用前景的催化方法逐步被研究验证.本文不仅系统性地介绍了光/热耦合电催化在二氧化碳和甲烷等小分子催化转化中的应用,而且对新型光/热耦合电催化剂的设计合成进行了展望.

Multimetallic AuPd@Pd@Pt core-interlayer-shell icosahedral electrocatalysts for highly efficient oxygen reduction reaction

Incorporating Pt with core metals into Pt-based core-shell catalysts is regarded as a promising strategy to substantially enhance the catalytic properties towards oxygen reduction reaction(ORR) in fuel cells due to the synergetic effect between distinct metals. In this wok, ultrathin Pt skins with two atomic layers were epitaxially coated on as-prepared icosahedral Au_50Pd_50, Au_60Pd_40 and Au_66Pd_34 nanocrystal seeds,which are constructed with alloyed cores and Pd shells with different thickness. Through electron microscopic characterizations, Pd interlayers with tunable thickness of 3, 6, and 12 atomic layers can be found in the Au_66Pd_34@Pt, Au_60 Pd_40@Pt and Au_50Pd_50@Pt icosahedra, respectively. These icosahedral Au Pd@Pd@Pt nanocrystals show substantially enhanced activities and durabilities in electrocatalytic measurements towards ORR compared to Au_75Pd_25@Pt icosahedra without Pd interlayer and commercial Pt/C catalysts. Specifically, Au_60Pd_40@Pt icosahedra with 6 atomically thick Pd interlayer display the best electrocatalytic performances, whose mass activities before and after durability tests of 50,000 cycles are11.6 and 30.2 times, respectively, as high as that of the commercial Pt/C.

近红外量子点发光二极管用于模拟神经突触可塑性（英文）

为了提高近红外发光二极管的性能,我们利用聚3-己基噻吩(P3HT)空穴迁移率高和对近红外光没有吸收的特点,将其作为器件的空穴传输层.实验发现,P3HT改善了基于硅量子点的近红外发光二极管的空穴/电子传输不平衡的现象.进一步地,将聚[9,9-二(3'-(N,N-二甲胺基)丙基)-2,7-芴-交-2,7-(9,9-二辛基芴)](PFN)作为中间层修饰P3HT,近红外硅量子点发光二极管的性能得到了更大改善,其外量子效率和功率效率分别达到了3.4%和4.4%.性能改善后的近红外硅量子点发光二极管可以用于模拟神经突触的可塑性,如短时程可塑性和长时程可塑性.

Atomistic Surface Passivation of CH_(3)NH_(3)PbI_(3) Perovskite Single Crystals for Highly Sensitive Coplanar-Structure X-Ray Detectors

Organic-inorganic halide perovskites(OIHPs)are recognized as the promising next-generation X-ray detection materials.However,the device performance is largely limited by the ion migration issue of OIHPs.Here,we reported a simple atomistic surface passivation strategy with methylammonium iodide(MAI)to remarkably increase the ion migration activation energy of CH_(3)NH_(3)PbI_(3)single crystals.The amount of MAI deposited on the crystal surface is finely regulated by a self-assemble process to effectively suppress the metallic lead defects,while not introducing extra mobile ions,which results in significantly improved dark current stability of the coplanar-structure devices under a large electric field of 100Vmm^(-1).The X-ray detectors hence exhibit a record-high sensitivity above 700,000μC Gy^(-1)_(air) cm^(-2)under continuum X-ray irradiation with energy up to 50 keV,which enables an ultralow X-ray detection limit down to 1.5 nGy_(air)s^(-1).Our findings will allow for the dramatically reduced X-ray exposure of human bodies in medical imaging applications.

An industrial solution to light-induced degradation of crystalline silicon solar cells

Boron-oxygen defects can cause serious lightinduced degradation （LID） of commercial solar cells based on the boron-doped crystalline silicon （c-Si）, which are formed under the injection of excess carriers induced either by illumination or applying forward bias. In this contribution, we have demonstrated that the passivation process of boron-oxygen defects can be induced by applying forward bias for a large quantity of solar cells, which is much more economic than light illumination. We have used this strategy to trigger the passivation process of batches of aluminum back surface field （A1-BSF） solar cells and passivated emitter and rear contact （PERC） solar cells. Both kinds of the treated solar cells show high stability in efficiency and suffer from very little LID under further illumination at room temperature. This technology is of significance for the suppression of LID of c-Si solar cells for the industrial manufacture.