Two-dimensional(2D)moirésuperlattices with a small twist in orientation exhibit a broad range of physical properties due to the complicated intralayer and interlayer interactions modulated by the twist angle.Here...Two-dimensional(2D)moirésuperlattices with a small twist in orientation exhibit a broad range of physical properties due to the complicated intralayer and interlayer interactions modulated by the twist angle.Here,we report a metal-semiconductor phase transition in homojunction moirésuperlattices of NiS_(2) and PtTe_(2) with large twist angles based on high-throughput screening of 2D materials MX_(2)(M=Ni,Pd,Pt;X=S,Se,Te)via density functional theory(DFT)calculations.Firstly,the calculations for different stacking configurations(AA,AB and AC)reveal that AA stacking ones are stable for all the bilayer MX_(2).The metallic or semiconducting properties of these 2D materials remain invariable for different stacking without twisting except for NiS_(2) and PtTe_(2).For the twisted configurations,NiS_(2) transfers from metal to semiconductor when the twist angles are 21.79°,27.79°,32.20°and 60°.PtTe_(2) exhibits a similar transition at 60°.The phase transition is due to the weakened d-p orbital hybridization around the Fermi level as the interlayer distance increases in the twisted configurations.Further calculations of untwisted bilayers with increasing interlayer distance demonstrate that all the materials undergo metal-semiconductor phase transition with the increased interlayer distance because of the weakened d-p orbital hybridization.These findings provide fundamental insights into tuning the electronic properties of moirésuperlattices with large twist angles.展开更多
An improved 4H-SiC metal-semiconductor field-effect transistors （MESFETs） with step p-buffer layer is proposed, and the static and dynamic electrical performances are analysed in this paper. A step p-buffer layer ha...An improved 4H-SiC metal-semiconductor field-effect transistors （MESFETs） with step p-buffer layer is proposed, and the static and dynamic electrical performances are analysed in this paper. A step p-buffer layer has been applied not only to increase the channel current, but also to improve the transconductance. This is due to the fact that the variation in p-buffer layer depth leads to the decrease in parasitic series resistance resulting from the change in the active channel thickness and modulation in the electric field distribution inside the channel. Detailed numerical simulations demonstrate that the saturation drain current and the maximum theoretical output power density of the proposed structure are about 30% and 37% larger than those of the conventional structure. The cut-off frequency and the maximum oscillation frequency of the proposed MESFETs are 14.5 and 62 GHz, respectively, which are higher than that of the conventional structure. Therefore, the 4H-SiC MESFETs with step p-buffer layer have superior direct-current and radio-frequency performances compared to the similar devices based on the conventional structure.展开更多
Sub-threshold characteristics of the dual material gate 4H-SiC MESFET （DMGFET） are investigated and the analytical models to describe the drain-induced barrier lowering （DIBL） effect are derived by solving one- an...Sub-threshold characteristics of the dual material gate 4H-SiC MESFET （DMGFET） are investigated and the analytical models to describe the drain-induced barrier lowering （DIBL） effect are derived by solving one- and two- dimensional Poisson＇s equations. Using these models, we calculate the bottom potential of the channel and the threshold voltage shift, which characterize the drain-induced barrier lowering （DIBL） effect. The calculated results reveal that the dual material gate （DMG） structure alleviates the deterioration of the threshold voltage and thus suppresses the DIBL effect due to the introduced step function, which originates from the work function difference of the two gate materials when compared with the conventional single material gate metal-semiconductor field-effect transistor （SMGFET）.展开更多
A metal-semiconductor composite with the interracial shells is investigated theoretically for the large linear mag- netoresistance effect of high doping Ag2＋δ Se and Ag2＋δ te materials. The magnetoresistance （MR...A metal-semiconductor composite with the interracial shells is investigated theoretically for the large linear mag- netoresistance effect of high doping Ag2＋δ Se and Ag2＋δ te materials. The magnetoresistance （MR） of composites is a function of the magnetic field, temperature, the conductivities of two phases without magnetic field, and the thickness and conductivity of the interracial shells. The MR increases with the increase of the magnetic field and with the decrease of temperature, and no saturation is found even under the high magnetic field. Moreover, it is interestingly found that the interracial shell is an important factor for the MR of the composites. The MR increases with the thickness and the conductivity of the interfacial shells. Lastly, the theoretical results on the MR are compared with the experimental data. It is found that the value of the MR of the composite with the interfacial shell is larger than that without the interfacial shell.展开更多
A complete model of Metal-Semiconductor-Metal Photodetector(MSM-PD) is presented. It can be used in any circuit simulators. Simulated DC characteristics for a GaAs MSM-PD are in good agreement with reported results.
Variable-energy positron annihilation spectroscopy has been applied to study interfaces in Al/Si, Au/Si and Au/GaAs structures. Computational fittings of ROYPROF program were used to analyze Doppler broadening results...Variable-energy positron annihilation spectroscopy has been applied to study interfaces in Al/Si, Au/Si and Au/GaAs structures. Computational fittings of ROYPROF program were used to analyze Doppler broadening results in order to determine kinds of regions that positrons were likely to sample. The interfaces were found acting as a capturing thin layer with negligible positrons stopped in them and their characteristics came only from positrons diffusing to these interfaces, the positron work function of these materials were taken into consideration. In all fittings, the interfaces are found to have 1 nm thickness and act as an absorbing sink for all thermal positrons diffusing towards them, and this indicates either the existence of open volume defects or a weakness of known theoretical models for positron affinities. The result is supported by measurements obtained by applying external electric fields on Al/Si sample. Theoretical fittings have clearly demonstrated the sensitivity of interfaces in these attempts and their importance in data analyzing and in developing of fitting cods.展开更多
Two-dimensional(2D)heterostructures based on layered transition metal dichalcogenides(TMDs)have attracted increasing attention for the applications of the nextgeneration high-performance integrated electronics and opt...Two-dimensional(2D)heterostructures based on layered transition metal dichalcogenides(TMDs)have attracted increasing attention for the applications of the nextgeneration high-performance integrated electronics and optoelectronics.Although various TMD heterostructures have been successfully fabricated,epitaxial growth of such atomically thin metal-semiconductor heterostructures with a clean and sharp interface is still challenging.In addition,photodetectors based on such heterostructures have seldom been studied.Here,we report the synthesis of high-quality vertical NbS2/MoS2metallic-semiconductor heterostructures.By using NbS2as the contact electrodes,the field-effect mobility and current on-off ratio of MoS2can be improved at least 6-fold and two orders of magnitude compared with the conventional Ti/Au contact,respectively.By using NbS2as contact,the photodetector performance of MoS2is much improved with higher responsivity and less response time.Such facile synthesis of atomically thin metal-semiconductor heterostructures by a simple chemical vapor deposition strategy and its effectiveness as ultrathin 2D metal contact open the door for the future application of electronics and optoelectronics.展开更多
Plasmonic metal-semiconductor nano-heterojuncfions （NHJs）, with their superior photocatalytic performance, provide opportunities for the efficient utilization of solar energy. However, scientific significance and te...Plasmonic metal-semiconductor nano-heterojuncfions （NHJs）, with their superior photocatalytic performance, provide opportunities for the efficient utilization of solar energy. However, scientific significance and technical challenges remain in the development of suitable metal-semiconductor NHJ photoelectrodes for new generation flexible optoelectronic devices, which often require complex processing. Herein, we report integrated three-dimensional （3D） NHJ photoelectrodes by conformally coating cadmium sulfide （CdS） nanolayers onto ultrathin nano- porous gold （NPG） films via a facile electrodeposition method. Localized surface plasmon resonance （LSPR） of NPG enhances the electron-hole pair generation and separation. Moreover, the direct contact interface and high conductive framework structure of the NHJs boosts the photogenerated carrier separation and transport. Hence, the NHJs exhibit evidently enhanced photocurrent density and hydrogen evolution rate relative to CdS deposited on either gold （Au） foil or fluorine-doped tin oxide （FTO） at 0 V vs. SCE （saturated calomel electrode） under visible-light irradiation. Moreover, they demonstrate a surprisingly stable photoelectrochemical hydrogen evolution （PEC-HE） activity over 104 s of continuous irradiation.展开更多
Emerging engineering strategies of colloidal metal-semiconductor nanorod hybrid nanostructures spanning from type,size,dimension,and location of both metal nanoparticles and semiconductors,co-catalyst,band gap structu...Emerging engineering strategies of colloidal metal-semiconductor nanorod hybrid nanostructures spanning from type,size,dimension,and location of both metal nanoparticles and semiconductors,co-catalyst,band gap structure,surface ligand to hole scavenger are elaborated symmetrically to rationalize the design of this type of intriguing materials for efficient photocatalytic applications.展开更多
Van der Waals (vdWs) stacking of two-dimensional (2D) materials can effectively weaken the Fermi level pinning (FLP) effect in metal/semiconductor contacts due to dangling-bond-free surfaces. However, the inherent vdW...Van der Waals (vdWs) stacking of two-dimensional (2D) materials can effectively weaken the Fermi level pinning (FLP) effect in metal/semiconductor contacts due to dangling-bond-free surfaces. However, the inherent vdWs gap always induces a considerable tunneling barrier, significantly limiting carrier injection. Herein, by inducing a sp^(2) to sp^(3) hybridization transformation in 2D carbon-based metal via surface defect engineering, the large orbital overlap can form an efficient carrier channel, overcoming the tunneling barrier. Specifically, by selecting the 2D carbon-based X_(3)C_(2) (X = Cd, Hg, and Zn) metal and the 2D MSi_(2)N_(4) (M = Cr, Hf, Mo, Ti, V, and Zr) semiconductor, we constructed 36 metal/semiconductor contacts. For vdWs contacts, although Ohmic contacts can be formed at the interface, the highest tunneling probability (P TB) is only 3.11%. As expected, the P TB can be significantly improved, as high as 48.73%, when MSi_(2)N_(4), accompanied by surface nitrogen vacancies, forms an interface covalent bond with X_(3)C_(2). Simultaneously, weak FLP and Ohmic contact remain at the covalent-bond-based surface, attributing to the protection of the MSi_(2)N_(4) band-edge electronic states by the outlying Si-N sublayer. Our work provides a promising path for advancing the progress of 2D electronic and photoelectronic devices.展开更多
The current-voltage （I-V） characteristics of 4H-SiC metal-semiconductor-metal （MSM） ultraviolet photodetector with different finger widths and spacings, different carrier concentrations and thicknesses of n-type e...The current-voltage （I-V） characteristics of 4H-SiC metal-semiconductor-metal （MSM） ultraviolet photodetector with different finger widths and spacings, different carrier concentrations and thicknesses of n-type epitaxial layer are simulated. The simulation results indicate that the dark current and the photocurrent both increase when the finger width increases. But the effect of finger width on the dark current is more significant. On the other hand, the effect of finger spacing on the photocurrent is more significant. When the finger spacing increases, the photocurrent decreases and the dark current is almost changeless. In addition, it is found that the smaller the carrier concentration of n-type epitaxial layer is, the smaller the dark current and the larger the photocurrent will be. It is also found that I-V characteristics of MSM detector also depend on the epitaxial layer thickness. The dark current of detector is smaller and the photocurrent is larger when the epitaxial layer thickness is about 3μm.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52472153,11704081,62488201)the National Key Research and Development Program of China(Grant No.2022YFA1204100)+2 种基金National Science and Technology Innovation Talent Cultivation Program(Grant No.2023BZRC016)Guangxi Natural Science Foundation(Grant No.2020GXNSFAA297182)the special fund for“Guangxi Bagui Scholars”。
文摘Two-dimensional(2D)moirésuperlattices with a small twist in orientation exhibit a broad range of physical properties due to the complicated intralayer and interlayer interactions modulated by the twist angle.Here,we report a metal-semiconductor phase transition in homojunction moirésuperlattices of NiS_(2) and PtTe_(2) with large twist angles based on high-throughput screening of 2D materials MX_(2)(M=Ni,Pd,Pt;X=S,Se,Te)via density functional theory(DFT)calculations.Firstly,the calculations for different stacking configurations(AA,AB and AC)reveal that AA stacking ones are stable for all the bilayer MX_(2).The metallic or semiconducting properties of these 2D materials remain invariable for different stacking without twisting except for NiS_(2) and PtTe_(2).For the twisted configurations,NiS_(2) transfers from metal to semiconductor when the twist angles are 21.79°,27.79°,32.20°and 60°.PtTe_(2) exhibits a similar transition at 60°.The phase transition is due to the weakened d-p orbital hybridization around the Fermi level as the interlayer distance increases in the twisted configurations.Further calculations of untwisted bilayers with increasing interlayer distance demonstrate that all the materials undergo metal-semiconductor phase transition with the increased interlayer distance because of the weakened d-p orbital hybridization.These findings provide fundamental insights into tuning the electronic properties of moirésuperlattices with large twist angles.
基金Project supported by the Fundamental Research Funds for the Central Universities(Grant No.ZYGX2009J029)
文摘An improved 4H-SiC metal-semiconductor field-effect transistors （MESFETs） with step p-buffer layer is proposed, and the static and dynamic electrical performances are analysed in this paper. A step p-buffer layer has been applied not only to increase the channel current, but also to improve the transconductance. This is due to the fact that the variation in p-buffer layer depth leads to the decrease in parasitic series resistance resulting from the change in the active channel thickness and modulation in the electric field distribution inside the channel. Detailed numerical simulations demonstrate that the saturation drain current and the maximum theoretical output power density of the proposed structure are about 30% and 37% larger than those of the conventional structure. The cut-off frequency and the maximum oscillation frequency of the proposed MESFETs are 14.5 and 62 GHz, respectively, which are higher than that of the conventional structure. Therefore, the 4H-SiC MESFETs with step p-buffer layer have superior direct-current and radio-frequency performances compared to the similar devices based on the conventional structure.
基金Project supported by the Pre-research Foundation from the National Ministries and Commissions of China (GrantNo.51308030201)
文摘Sub-threshold characteristics of the dual material gate 4H-SiC MESFET （DMGFET） are investigated and the analytical models to describe the drain-induced barrier lowering （DIBL） effect are derived by solving one- and two- dimensional Poisson＇s equations. Using these models, we calculate the bottom potential of the channel and the threshold voltage shift, which characterize the drain-induced barrier lowering （DIBL） effect. The calculated results reveal that the dual material gate （DMG） structure alleviates the deterioration of the threshold voltage and thus suppresses the DIBL effect due to the introduced step function, which originates from the work function difference of the two gate materials when compared with the conventional single material gate metal-semiconductor field-effect transistor （SMGFET）.
基金Supported by the China Postdoctoral Science Foundation under Grant No 2014MM551868the Science and Technology Development Guidance Program of Qingdao under Grant No KJZD-13-35-JCH
文摘A metal-semiconductor composite with the interracial shells is investigated theoretically for the large linear mag- netoresistance effect of high doping Ag2＋δ Se and Ag2＋δ te materials. The magnetoresistance （MR） of composites is a function of the magnetic field, temperature, the conductivities of two phases without magnetic field, and the thickness and conductivity of the interracial shells. The MR increases with the increase of the magnetic field and with the decrease of temperature, and no saturation is found even under the high magnetic field. Moreover, it is interestingly found that the interracial shell is an important factor for the MR of the composites. The MR increases with the thickness and the conductivity of the interfacial shells. Lastly, the theoretical results on the MR are compared with the experimental data. It is found that the value of the MR of the composite with the interfacial shell is larger than that without the interfacial shell.
文摘A complete model of Metal-Semiconductor-Metal Photodetector(MSM-PD) is presented. It can be used in any circuit simulators. Simulated DC characteristics for a GaAs MSM-PD are in good agreement with reported results.
文摘Variable-energy positron annihilation spectroscopy has been applied to study interfaces in Al/Si, Au/Si and Au/GaAs structures. Computational fittings of ROYPROF program were used to analyze Doppler broadening results in order to determine kinds of regions that positrons were likely to sample. The interfaces were found acting as a capturing thin layer with negligible positrons stopped in them and their characteristics came only from positrons diffusing to these interfaces, the positron work function of these materials were taken into consideration. In all fittings, the interfaces are found to have 1 nm thickness and act as an absorbing sink for all thermal positrons diffusing towards them, and this indicates either the existence of open volume defects or a weakness of known theoretical models for positron affinities. The result is supported by measurements obtained by applying external electric fields on Al/Si sample. Theoretical fittings have clearly demonstrated the sensitivity of interfaces in these attempts and their importance in data analyzing and in developing of fitting cods.
基金This work was supported by the National Natural Science Foundation of China （Grant Nos. 41172110 and 61107090） and Shandong Provincial Natural Science Foundation （Grant No. ZR2011BZ007）.
基金financially supported by the National Key R&D Program of China(2018YFA0306900 and 2018YFA0305800)the National Natural Science Foundation of China(51872012)。
文摘Two-dimensional(2D)heterostructures based on layered transition metal dichalcogenides(TMDs)have attracted increasing attention for the applications of the nextgeneration high-performance integrated electronics and optoelectronics.Although various TMD heterostructures have been successfully fabricated,epitaxial growth of such atomically thin metal-semiconductor heterostructures with a clean and sharp interface is still challenging.In addition,photodetectors based on such heterostructures have seldom been studied.Here,we report the synthesis of high-quality vertical NbS2/MoS2metallic-semiconductor heterostructures.By using NbS2as the contact electrodes,the field-effect mobility and current on-off ratio of MoS2can be improved at least 6-fold and two orders of magnitude compared with the conventional Ti/Au contact,respectively.By using NbS2as contact,the photodetector performance of MoS2is much improved with higher responsivity and less response time.Such facile synthesis of atomically thin metal-semiconductor heterostructures by a simple chemical vapor deposition strategy and its effectiveness as ultrathin 2D metal contact open the door for the future application of electronics and optoelectronics.
基金This work was financially supported by the National Natural Science Foundation of China （No. 51671145）, the National Thousand Young Talents Program of China, the Tianjin Municipal Education Commission, the Tianjin Munidpal Science and Technology Commission （No. 16JCYBJC17000） and the Fundamental Research Funds of Tianjin University of Technology. We would like to thank Dr. Anna Carlsson from FEI Company for her assistance with the atomic-resolution structure and EELS analyses, and Y. D. also acknowledges useful discussions and experimental assistance from Dr. Yajun Gao, Dr. Rongyue Wang, Dr. Chuancheng Jia, Xuanxuan Bi, and Junli Liu.
文摘Plasmonic metal-semiconductor nano-heterojuncfions （NHJs）, with their superior photocatalytic performance, provide opportunities for the efficient utilization of solar energy. However, scientific significance and technical challenges remain in the development of suitable metal-semiconductor NHJ photoelectrodes for new generation flexible optoelectronic devices, which often require complex processing. Herein, we report integrated three-dimensional （3D） NHJ photoelectrodes by conformally coating cadmium sulfide （CdS） nanolayers onto ultrathin nano- porous gold （NPG） films via a facile electrodeposition method. Localized surface plasmon resonance （LSPR） of NPG enhances the electron-hole pair generation and separation. Moreover, the direct contact interface and high conductive framework structure of the NHJs boosts the photogenerated carrier separation and transport. Hence, the NHJs exhibit evidently enhanced photocurrent density and hydrogen evolution rate relative to CdS deposited on either gold （Au） foil or fluorine-doped tin oxide （FTO） at 0 V vs. SCE （saturated calomel electrode） under visible-light irradiation. Moreover, they demonstrate a surprisingly stable photoelectrochemical hydrogen evolution （PEC-HE） activity over 104 s of continuous irradiation.
基金supported by the Australian Research Council(ARC)Future Fellowship Scheme(FT210100509)ARC Discovery Project(DP220101959)+2 种基金the Hebrew University of Jerusalem--Zelman Cowen Academic Initiatives(zCAl)Joint Projects 2021,the Innovation and Technology Commission(grant no.MHP/104/21)Shenzhen Science Technology and Innovation Commission(grant no.20210324125612035)City University of Hong Kong(grant no.9360140).
文摘Emerging engineering strategies of colloidal metal-semiconductor nanorod hybrid nanostructures spanning from type,size,dimension,and location of both metal nanoparticles and semiconductors,co-catalyst,band gap structure,surface ligand to hole scavenger are elaborated symmetrically to rationalize the design of this type of intriguing materials for efficient photocatalytic applications.
基金supported by China Postdoctoral Science Foundation(No.2022M711691)the National Natural Science Foundation of China(Nos.12104130 and 12304085)+3 种基金Six talent peaks project in Jiangsu Province(No.XCL-104)the open research fund of Key Laboratory of Quantum Materials and Devices(Southeast University)Ministry of Education(No.3207022401C3)Natural Science Foundation of Nanjing University of Posts and Telecommunications(No.NY221102).
文摘Van der Waals (vdWs) stacking of two-dimensional (2D) materials can effectively weaken the Fermi level pinning (FLP) effect in metal/semiconductor contacts due to dangling-bond-free surfaces. However, the inherent vdWs gap always induces a considerable tunneling barrier, significantly limiting carrier injection. Herein, by inducing a sp^(2) to sp^(3) hybridization transformation in 2D carbon-based metal via surface defect engineering, the large orbital overlap can form an efficient carrier channel, overcoming the tunneling barrier. Specifically, by selecting the 2D carbon-based X_(3)C_(2) (X = Cd, Hg, and Zn) metal and the 2D MSi_(2)N_(4) (M = Cr, Hf, Mo, Ti, V, and Zr) semiconductor, we constructed 36 metal/semiconductor contacts. For vdWs contacts, although Ohmic contacts can be formed at the interface, the highest tunneling probability (P TB) is only 3.11%. As expected, the P TB can be significantly improved, as high as 48.73%, when MSi_(2)N_(4), accompanied by surface nitrogen vacancies, forms an interface covalent bond with X_(3)C_(2). Simultaneously, weak FLP and Ohmic contact remain at the covalent-bond-based surface, attributing to the protection of the MSi_(2)N_(4) band-edge electronic states by the outlying Si-N sublayer. Our work provides a promising path for advancing the progress of 2D electronic and photoelectronic devices.
基金the National Defense Pre-Research Foundation of China.
文摘The current-voltage （I-V） characteristics of 4H-SiC metal-semiconductor-metal （MSM） ultraviolet photodetector with different finger widths and spacings, different carrier concentrations and thicknesses of n-type epitaxial layer are simulated. The simulation results indicate that the dark current and the photocurrent both increase when the finger width increases. But the effect of finger width on the dark current is more significant. On the other hand, the effect of finger spacing on the photocurrent is more significant. When the finger spacing increases, the photocurrent decreases and the dark current is almost changeless. In addition, it is found that the smaller the carrier concentration of n-type epitaxial layer is, the smaller the dark current and the larger the photocurrent will be. It is also found that I-V characteristics of MSM detector also depend on the epitaxial layer thickness. The dark current of detector is smaller and the photocurrent is larger when the epitaxial layer thickness is about 3μm.
