Demonstration of irradiation-resistant 4H-SiC based photoelectrochemical water splitting

4H silicon carbide(4H-SiC)has gained a great success in high-power electronics,owing to its advantages of wide bandgap,high breakdown electric field strength,high carrier mobility,and high thermal conductivity.Considering the high carrier mobility and high stability of 4H-SiC,4H-SiC has great potential in the field of photoelectrochemical(PEC)water splitting.In this work,we demonstrate the irradiation-resistant PEC water splitting based on nanoporous 4H-SiC arrays.A new two-step anodizing approach is adopted to prepare 4H-SiC nanoporous arrays with different porosity,that is,a constant low-voltage etching followed by a pulsed high-voltage etching.The constant-voltage etching and pulsed-voltage etching are adopted to control the diameter of the nanopores and the depth of the nanoporous arrays,respectively.It is found that the nanoporous arrays with medium porosity has the highest PEC current,because of the enhanced light absorption and the optimized transportation of charge carriers along the walls of the nanoporous arrays.The performance of the PEC water splitting of the nanoporous arrays is stable after the electron irradiation with the dose of 800 and 1600 k Gy,which indicates that 4H-SiC nanoporous arrays has great potential in the PEC water splitting under harsh environments.

Efficient Monolithic Perovskite/Silicon Tandem Photovoltaics

Tunable bandgaps make halide perovskites promising candidates for developing tandem solar cells(TSCs),a strategy to break the radiative limit of 33.7%for single-junction solar cells.Combining perovskites with market-dominant crystalline silicon(c-Si)is particularly attractive;simple estimates based on the bandgap matching indicate that the efficiency limit in such tandem device is as high as 46%.However,state-of-the-art perovskite/c-Si TSCs only achieve an efficiency of~32.5%,implying significant challenges and also rich opportunities.In this review,we start with the operating mechanism and efficiency limit of TSCs,followed by systematical discussions on wide-bandgap perovskite front cells,interface selective contacts,and electrical interconnection layer,as well as photon management for highly efficient perovskite/c-Si TSCs.We highlight the challenges in this field and provide our understanding of future research directions toward highly efficient and stable large-scale wide-bandgap perovskite front cells for the commercialization of perovskite/c-Si TSCs.

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).

Defects evolution in n-type 4H-SiC induced by electron irradiation and annealing

Radiation damage produced in 4H-SiC by electrons of different doses is presented by using multiple characterization techniques. Raman spectra results indicate that SiC crystal structures are essentially impervious to 10 Me V electron irradiation with doses up to 3000 kGy. However, irradiation indeed leads to the generation of various defects, which are evaluated through photoluminescence(PL) and deep level transient spectroscopy(DLTS). The PL spectra feature a prominent broad band centered at 500 nm, accompanied by several smaller peaks ranging from 660 to 808 nm. The intensity of each PL peak demonstrates a linear correlation with the irradiation dose, indicating a proportional increase in defect concentration during irradiation. The DLTS spectra reveal several thermally unstable and stable defects that exhibit similarities at low irradiation doses.Notably, after irradiating at the higher dose of 1000 kGy, a new stable defect labeled as R_(2)(Ec-0.51 eV) appeared after annealing at 800 K. Furthermore, the impact of irradiation-induced defects on SiC junction barrier Schottky diodes is discussed. It is observed that high-dose electron irradiation converts SiC n-epilayers to semi-insulating layers. However, subjecting the samples to a temperature of only 800 K results in a significant reduction in resistance due to the annealing out of unstable defects.

A highly sensitive ratiometric near-infrared nanosensor based on erbium-hyperdoped silicon quantum dots for iron(Ⅲ) detection

Ratiometric fluorescent detection of iron(Ⅲ)(Fe^(3+))offers inherent self-calibration and contactless analytic capabilities.However,realizing a dual-emission near-infrared(NIR)nanosensor with a low limit of detection(LOD)is rather challenging.In this work,we report the synthesis of water-dispersible erbium-hyperdoped silicon quantum dots(Si QDs:Er),which emit NIR light at the wavelengths of 810 and 1540 nm.A dual-emission NIR nanosensor based on water-dispersible Si QDs:Er enables ratiometric Fe^(3+)detection with a very low LOD(0.06μM).The effects of pH,recyclability,and the interplay between static and dynamic quenching mechanisms for Fe^(3+)detection have been systematically studied.In addition,we demonstrate that the nanosensor may be used to construct a sequential logic circuit with memory functions.

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.

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.

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).

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.

Silicon-based optoelectronic synaptic devices

High-performance neuromorphic computing(i.e.,brain-like computing)is envisioned to seriously demand optoelectronically integrated artificial neural networks(ANNs)in the future.Optoelectronic synaptic devices are critical building blocks for optoelectronically integrated ANNs.For the large-scale deployment of high-performance neuromorphic computing in the future,it would be advantageous to fabricate optoelectronic synaptic devices by using advanced silicon(Si)technologies.This calls for the development of Si-based optoelectronic synaptic devices.In this work we review the use of Si materials to make optoelectronic synaptic devices,which have either two-terminal or three-terminal structures.A series of important synaptic functionalities have been well mimicked by using these Si-based optoelectronic synaptic devices.We also present the outlook of using Si materials for optoelectronic synaptic devices.

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.

Information & Functional Materials: An interdisciplinary platform exploring the frontiers of functional materials, nanotechnologies, and informatics

Information and functional materials are pivotal in powering scientific and technological advancements of modern societies.The continuous progresses and achievements made from functional materials and nanotechnologies have driven the development of smarter,faster,and more efficient informatics and optoelectronics.Concurrently,technological innovations such as green energy and artificial intelligence,etc.,cannot be realized without the breakthrough of functional materials.These collective progresses are vital in resolving social and climate challenges.Given the photovoltaics as an example.

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.

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.

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.

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.

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.