To address the urgent demand for the miniaturization and multifunctional integration of high-frequency Rayleigh surface wave devices in 5G communication technology,the propagation characteristics of Rayleigh surface w...To address the urgent demand for the miniaturization and multifunctional integration of high-frequency Rayleigh surface wave devices in 5G communication technology,the propagation characteristics of Rayleigh surface waves in an elastic half-space attached by a nanoscale piezoelectric semiconductor(PSC)thin layer with flexoelectricity and size-effects are systematically investigated.Based on the Hamiltonian principle,the elastic dynamic equations and Gauss's theorem of electrostatics are obtained.The eigenvalue problem is numerically solved with a genetic algorithm in MATLAB,and the dispersion properties are obtained.The effects of various key factors,including the flexoelectricity,inertia gradients,strain gradients,electric field gradients,PSC layer thickness,steady-state carrier concentration,and bias electric fields,on the propagation and attenuation characteristics of Rayleigh surface waves are analyzed.The results demonstrate that the increases in the flexoelectric coefficient and strain gradient characteristic length lead to an increase in the real part of the complex phase velocity,while the increases in the inertia gradient characteristic length,electric field gradient characteristic length,PSC layer thickness,and steady-state carrier concentration result in a decrease.Additionally,the bias electric fields significantly influence the Rayleigh surface wave attenuation.The present findings are crucial for the accurate property evaluation of miniaturized highfrequency Rayleigh wave devices,and provide valuable theoretical support for their design and optimization.展开更多
By formation of an intermediate semiconductor layer （ISL） with a narrow band gap at the metallic contact/SiC interface, this paper realises a new method to fabricate the low-resistance Ohmic contacts for SiC. An arr...By formation of an intermediate semiconductor layer （ISL） with a narrow band gap at the metallic contact/SiC interface, this paper realises a new method to fabricate the low-resistance Ohmic contacts for SiC. An array of transfer length method （TLM） test patterns is formed on N-wells created by P＋ ion implantation into Si-faced p-type 4H- SiC epilayer. The ISL of nickel-metal Ohmic contacts to n-type 4H-SiC could be formed by using Germanium ion implantation into SiC. The specific contact resistance pc as low as 4.23×10-5Ω·cm2 is achieved after annealing in N2 at 800 ℃ for 3 min, which is much lower than that （〉 900℃） in the typical SiC metallisation process. The sheet resistance Rsh of the implanted layers is 1.5 kΩ/□. The technique for converting photoresist into nanocrystalline graphite is used to protect the SiC surface in the annealing after Ge＋ ion implantations.展开更多
We describe theoretically the grounded method of measuring the conductivity of anisotropic layered semiconductor materials. The suggested method implies the use of a four-probe testing device with a linear arrangement...We describe theoretically the grounded method of measuring the conductivity of anisotropic layered semiconductor materials. The suggested method implies the use of a four-probe testing device with a linear arrangement of probes. The final expressions for identifying the electrical conductivity are presented in the form of a series of analytic functions. The suggested method is experimentally verified, and practical recommendations of how to apply it are also provided.展开更多
Si-based multilayer structures are widely used in current microelectronics. During their preparation, some inhomogeneous residual stress is induced, resulting in competition between interface mismatching and surface e...Si-based multilayer structures are widely used in current microelectronics. During their preparation, some inhomogeneous residual stress is induced, resulting in competition between interface mismatching and surface energy and even leading to structure failure. This work presents a methodological study on the measurement of residual stress in a multi-layer semiconductor heterostructure. Scanning electron microscopy（SEM）, micro-Raman spectroscopy（MRS）, and transmission electron microscopy（TEM） were applied to measure the geometric parameters of the multilayer structure. The relationship between the Raman spectrum and the stress/strain on the [100] and [110] crystal orientations was determined to enable surface and crosssection residual stress analyses, respectively. Based on the Raman mapping results, the distribution of residual stress along the depth of the multi-layer heterostructure was successfully obtained.展开更多
As Moore’s law deteriorates,the research and development of new materials system are crucial for transitioning into the post Moore era.Traditional semiconductor materials,such as silicon,have served as the cornerston...As Moore’s law deteriorates,the research and development of new materials system are crucial for transitioning into the post Moore era.Traditional semiconductor materials,such as silicon,have served as the cornerstone of modern technologies for over half a century.This has been due to extensive research and engineering on new techniques to continuously enrich silicon-based materials system and,subsequently,to develop better performed silicon-based devices.Meanwhile,in the emerging post Moore era,layered semiconductor materials,such as transition metal dichalcogenides(TMDs),have garnered considerable research interest due to their unique electronic and optoelectronic properties,which hold great promise for powering the new era of next generation electronics.As a result,techniques for engineering the properties of layered semiconductors have expanded the possibilities of layered semiconductor-based devices.However,there remain significant limitations in the synthesis and engineering of layered semiconductors,impeding the utilization of layered semiconductor-based devices for mass applications.As a practical alternative,heterogeneous integration between layered and traditional semiconductors provides valuable opportunities to combine the distinctive properties of layered semiconductors with well-developed traditional semiconductors materials system.Here,we provide an overview of the comparative coherence between layered and traditional semiconductors,starting with TMDs as the representation of layered semiconductors.We highlight the meaningful opportunities presented by the heterogeneous integration of layered semiconductors with traditional semiconductors,representing an optimal strategy poised to propel the emerging semiconductor research community and chip industry towards unprecedented advancements in the coming decades.展开更多
In recent years,valleytronics researches based on 2D semiconducting transition metal dichalcogenides have attracted considerable attention.On the one hand,strong spin–orbit interaction allows the presence of spin–va...In recent years,valleytronics researches based on 2D semiconducting transition metal dichalcogenides have attracted considerable attention.On the one hand,strong spin–orbit interaction allows the presence of spin–valley coupling in this system,which provides spin addressable valley degrees of freedom for information storage and processing.On the other hand,large exciton binding energy up to hundreds of me V enables excitons to be stable carriers of valley information.Valley polarization,marked by an imbalanced exciton population in two inequivalent valleys(+K and-K),is the core of valleytronics as it can be utilized to store binary information.Motivated by the potential applications,we present a thorough overview of the recent advancements in the generation,relaxation,manipulation,and transport of the valley polarization in nonmagnetic transition metal dichalcogenide layered semiconductors.We also discuss the development of valleytronic devices and future challenges in this field.展开更多
According to the Fowler theory and numerous experiments the quantum efficiency for photoemission from conductors increases with temperature. Here we show that an opposite temperature dependence is also possible, when ...According to the Fowler theory and numerous experiments the quantum efficiency for photoemission from conductors increases with temperature. Here we show that an opposite temperature dependence is also possible, when the photoemission is from quasi-metallic surface accumulation layers of n-type semiconductors. This is due to the temperature dependence of the Fermi level energy in semiconductors. The Fermi level energy increases with decreasing temperature;this leads to a decrease of the semiconductor work function and consequently an increase of the quantum efficiency photoemission at constant value of absorbed light quanta of energy. We have calculated this effect for electron accumulation layer in n-GaN, induced by adsorption of positively charged cesium or barium ions. It is found that at low temperatures near liquid nitrogen, the quantum efficiency for photoemission increases to near 55%, which is comparable to the largest values, reported for any known photo-ca-thodes. This phenomenon may prove useful for efficient photo-cathodes operating at low temperatures.展开更多
Atomically thin two-dimensional(2D) materials are the building bricks for next-generation electronics and optoelectronics, which demand plentiful functional properties in mechanics, transport, magnetism and photorespo...Atomically thin two-dimensional(2D) materials are the building bricks for next-generation electronics and optoelectronics, which demand plentiful functional properties in mechanics, transport, magnetism and photoresponse.For electronic devices, not only metals and high-performance semiconductors but also insulators and dielectric materials are highly desirable. Layered structures composed of 2D materials of different properties can be delicately designed as various useful heterojunction or homojunction devices, in which the designs on the same material(namely homojunction) are of special interest because preparation techniques can be greatly simplified and atomically seamless interfaces can be achieved. We demonstrate that the insulating pristine ZnPS_3, a ternary transition-metal phosphorus trichalcogenide, can be transformed into a highly conductive metal and an n-type semiconductor by intercalating Co and Cu atoms, respectively. The field-effect-transistor(FET) devices are prepared via an ultraviolet exposure lithography technique. The Co-ZnPS_3 device exhibits an electrical conductivity of 8 × 10^(4) S/m, which is comparable to the conductivity of graphene. The Cu-ZnPS_3 FET reveals a current ON/OFF ratio of 1-05 and a mobility of 3 × 10^(-2 )cm^(2)·V^(-1)·s^(-1). The realization of an insulator, a typical semiconductor and a metallic state in the same 2D material provides an opportunity to fabricate n-metal homojunctions and other in-plane electronic functional devices.展开更多
Al-doped ZnO thin film （AZO） is used as a subcontact layer in 6H-SiC photoconductive semiconductor switches （PCSSs） to reduce the on-state resistance and optimize the device structure. Our photoconductive test sho...Al-doped ZnO thin film （AZO） is used as a subcontact layer in 6H-SiC photoconductive semiconductor switches （PCSSs） to reduce the on-state resistance and optimize the device structure. Our photoconductive test shows that the onstate resistance of lateral PCSS with an n＋-AZO subcontact layer is 14.7% lower than that of PCSS without an n＋-AZO subcontact layer. This occurs because a heavy-doped AZO thin film can improve Ohmic contact properties, reduce contact resistance, and alleviate Joule heating. Combined with the high transparance characteristic at 532 nm of AZO film, vertical structural PCSS devices are designed and their structural superiority is discussed. This paper provides a feasible route for fabricating high performance SiC PCSS by using conductive and transparent ZnO-based materials.展开更多
[FeNi（3 nm）/Zn1-xCoxO（3 nm）]2/ZnO（d nm）/[Zn1-xCoxO（3 nm）/Co（3 nm）]2 （d=3 and 10） semiconductor junctions were prepared by magnetron sputtering system and photolithography. The spin valve effect was observe...[FeNi（3 nm）/Zn1-xCoxO（3 nm）]2/ZnO（d nm）/[Zn1-xCoxO（3 nm）/Co（3 nm）]2 （d=3 and 10） semiconductor junctions were prepared by magnetron sputtering system and photolithography. The spin valve effect was observed in these junctions because the utility of the ferromagnetic composite layers acted as soft and hard magnetic layers. The electrical detection was performed by measuring the magnetoresistance of these junctions to investigate the current spin polarization asc in the ZnO layer and the spin injection efficiency η of spin-polarized electrons. asc was reduced from 11.7% （and 10.5%） at 90 K to 7.31% （and 5.93%） at room temperature for d=3 （and d=10）. And η was reduced from 39.5% （and 35.5%） at 90 K to 24.7% （and 20.0%） at room temperature for d=3 （and d=10）.展开更多
Molecular Beam Epitaxy (MBE) system equipped with in-situ Reflection High-Energy Electron Diffraction (RHEED) has been used for (Ge, Mn) thin film growth and monitoring the surface morphology and crystal structure of ...Molecular Beam Epitaxy (MBE) system equipped with in-situ Reflection High-Energy Electron Diffraction (RHEED) has been used for (Ge, Mn) thin film growth and monitoring the surface morphology and crystal structure of thin films. Based on the observation of changes in RHEED patterns during nanocolumn growth, we used a real-time control approach to realize multilayer structures that consist of two nanocolumn layers separated by a Ge barrier layer. Transmission Electron Microscopy (TEM) has been used to investigate the structural properties of the GeMn nanocolumns and GeMn/Ge nanocolumns bi-layers samples.展开更多
Accumulation-type GaN metal-oxide-semiconductor field-effect transistors （MOSFETs） with atomic-layer- deposited A1203 gate dielectrics are fabricated. The device, with atomic-layer-deposited A1203 as the gate dielec...Accumulation-type GaN metal-oxide-semiconductor field-effect transistors （MOSFETs） with atomic-layer- deposited A1203 gate dielectrics are fabricated. The device, with atomic-layer-deposited A1203 as the gate dielectric, presents a drain current of 260 mA/mm and a broad maximum transconductance of 34 mS/mm, which are better than those reported previously with Al203 as the gate dielectric. Furthermore, the device shows negligible current collapse in a wide range of bias voltages, owing to the effective passivation of the GaN surface by the A1203 film. The gate drain breakdown voltage is found to be about 59.5 V, and in addition the channel mobility of the n-GaN layer is about 380 cm^2/Vs, which is consistent with the Hall result, and it is not degraded by atomic-layer-deposition A1203 growth and device fabrication.展开更多
Investigation of the electric properties of semi-conducting materials in an applied ac electric fields gives information about the nature of charge transport and localized states in the forbidden gap. Layered crystals...Investigation of the electric properties of semi-conducting materials in an applied ac electric fields gives information about the nature of charge transport and localized states in the forbidden gap. Layered crystals usually contain structural defects, such as dislocations and vacancies that may form a high density of localized states near the Fermi level. So, the current study was carried out for insight into the dielectric Properties of Tl2S layered single crystals. These properties were studied using the ac measurements in the low temperatures ranging from 77 to 300 K. The real part of dielectric constant ε?, imaginary part of dielectric constant ε?, the dissipation factor tan δ and the alternating current conductivity σac were measured in an applied ac electric field of frequencies extending from 2.5 to 50 kHz. Based on the dependencies of these dielectric parameters on both the frequency and temperature, the dielectric properties of the crystals under investigation were elucidated and analyzed. The ac conductivity was found to obey the power law σac(ω) = Aωs with which the values of the exponent s were evaluated to be less than unity in the range 0.21 ≥ s ≥ 0.19. Furthermore, it was found that the temperature dependence of ac conductivity follows the Arrhenius relation via which the impact of temperature on the electrical processes in an applied ac electric field was illustrated and analyzed. The influences of temperature and frequency on both the exponent s and band gap were also discussed in this investigation.展开更多
Amorphous states of two-dimensional(2D)materials frequently exhibit remarkable physical properties that differ significantly from their crystalline counterparts.Typically,metastable amorphous states can be achieved th...Amorphous states of two-dimensional(2D)materials frequently exhibit remarkable physical properties that differ significantly from their crystalline counterparts.Typically,metastable amorphous states can be achieved through rapid quenching from high temperatures.However,the heating process is detrimental to the structural integrity of 2D materials.In this study,we successfully utilized pressure as an external stimulus to induce an amorphous state in layered crystal SiP.Comprehensive experimental and theoretical investigations revealed metallization in the high-pressure amorphous phase of SiP.The recovered samples were characterized using x-ray diffraction,Raman spectroscopy,high-resolution transmission electron microscopy,and selected area electron diffraction.The results indicate that the metallic amorphous SiP obtained under extreme conditions can be stabilized at ambient conditions.These findings provide a viable pathway for inducing metastable phases in 2D materials and offer new insights into the design and development of advanced electronic devices.展开更多
Anti-Stokes photoluminescence(ASPL)in low-dimensional van der Waals(vdW)layered materials is becoming increasingly attractive for its potential in advanced applications such as optical cooling,sub-energy band detectio...Anti-Stokes photoluminescence(ASPL)in low-dimensional van der Waals(vdW)layered materials is becoming increasingly attractive for its potential in advanced applications such as optical cooling,sub-energy band detection and optoelectronic devices.While transition metal dichalcogenides(TMDCs),among the most studied vdW semiconductors for ASPL,exhibit a direct bandgap exclusively in their monolayer form.This characteristic results in a short light-matter interaction distance and thus low ASPL emission efficiency,which seriously impedes the advancement of ASPL in vdW layered materials.In contrast,transition metal halide lead iodide(PbI_(2)),a vdW semiconductor with a direct bandgap in a wide range of thicknesses(⩾3 layers)superior to TMDCs,has shown promise for ASPL.However,the reported ASPL emission efficiency of PbI_(2) is notably low.Moreover,scant research has focused on the rich ASPL emission states in PbI_(2),particularly concerning the assignment of these emission states.Here,through a designed thickness selection,we observed more detailed ASPL emissions in submicrometer-thick PbI_(2) at room temperature,in addition to a series of previously unreported ASPL emission peaks that emerge at low temperatures.Importantly,the low-temperature ASPL of PbI_(2) exhibits an approximate 1000-fold enhancement compared to that observed at room temperature.This significant enhancement is attributed to the transition from phonon-assisted one-photon absorption to two-step photon absorption induced by resonance absorption effect,as well as substantially reduced nonradiative decays at low temperatures.Our findings enhance the comprehensive understanding of ASPL in PbI_(2),holding great significance for the development of ASPL applications.展开更多
基金supported by the Singapore Ministry of Education(MOE)Academic Research Fund(AcRF)Tier 1(Nos.RG145/23 and RG78/24)the National Natural Science Foundation of China(No.U24A2005)Ningbo Natural Science Foundation(No.2024J183)。
文摘To address the urgent demand for the miniaturization and multifunctional integration of high-frequency Rayleigh surface wave devices in 5G communication technology,the propagation characteristics of Rayleigh surface waves in an elastic half-space attached by a nanoscale piezoelectric semiconductor(PSC)thin layer with flexoelectricity and size-effects are systematically investigated.Based on the Hamiltonian principle,the elastic dynamic equations and Gauss's theorem of electrostatics are obtained.The eigenvalue problem is numerically solved with a genetic algorithm in MATLAB,and the dispersion properties are obtained.The effects of various key factors,including the flexoelectricity,inertia gradients,strain gradients,electric field gradients,PSC layer thickness,steady-state carrier concentration,and bias electric fields,on the propagation and attenuation characteristics of Rayleigh surface waves are analyzed.The results demonstrate that the increases in the flexoelectric coefficient and strain gradient characteristic length lead to an increase in the real part of the complex phase velocity,while the increases in the inertia gradient characteristic length,electric field gradient characteristic length,PSC layer thickness,and steady-state carrier concentration result in a decrease.Additionally,the bias electric fields significantly influence the Rayleigh surface wave attenuation.The present findings are crucial for the accurate property evaluation of miniaturized highfrequency Rayleigh wave devices,and provide valuable theoretical support for their design and optimization.
基金Project supported by the National Natural Science Foundation of China (Grant No J54508250120)Xi’an Applied Materials Innovation Fund (Grant No XA-AM-200704)
文摘By formation of an intermediate semiconductor layer （ISL） with a narrow band gap at the metallic contact/SiC interface, this paper realises a new method to fabricate the low-resistance Ohmic contacts for SiC. An array of transfer length method （TLM） test patterns is formed on N-wells created by P＋ ion implantation into Si-faced p-type 4H- SiC epilayer. The ISL of nickel-metal Ohmic contacts to n-type 4H-SiC could be formed by using Germanium ion implantation into SiC. The specific contact resistance pc as low as 4.23×10-5Ω·cm2 is achieved after annealing in N2 at 800 ℃ for 3 min, which is much lower than that （〉 900℃） in the typical SiC metallisation process. The sheet resistance Rsh of the implanted layers is 1.5 kΩ/□. The technique for converting photoresist into nanocrystalline graphite is used to protect the SiC surface in the annealing after Ge＋ ion implantations.
基金Supported by the Ministry of Education and Science of the Russian Federation under Grant No 2271
文摘We describe theoretically the grounded method of measuring the conductivity of anisotropic layered semiconductor materials. The suggested method implies the use of a four-probe testing device with a linear arrangement of probes. The final expressions for identifying the electrical conductivity are presented in the form of a series of analytic functions. The suggested method is experimentally verified, and practical recommendations of how to apply it are also provided.
基金supported by the National Basic Research Program of China (Grant 2012CB937500)the National Natural Science Foundation of China (Grants 11422219, 11227202, 11372217, 11272232)+1 种基金the Program for New Century Excellent Talents in University (Grant NCET-13)China Scholarship Council (201308120092)
文摘Si-based multilayer structures are widely used in current microelectronics. During their preparation, some inhomogeneous residual stress is induced, resulting in competition between interface mismatching and surface energy and even leading to structure failure. This work presents a methodological study on the measurement of residual stress in a multi-layer semiconductor heterostructure. Scanning electron microscopy（SEM）, micro-Raman spectroscopy（MRS）, and transmission electron microscopy（TEM） were applied to measure the geometric parameters of the multilayer structure. The relationship between the Raman spectrum and the stress/strain on the [100] and [110] crystal orientations was determined to enable surface and crosssection residual stress analyses, respectively. Based on the Raman mapping results, the distribution of residual stress along the depth of the multi-layer heterostructure was successfully obtained.
基金supported by National Key R&D Program of China(2020YFB2008704)the National Natural Science Foundation of China(62004114 and 62174098)+1 种基金Beijing Municipal Science and Technology Commission(Z221100005822011)The Tsinghua-Foshan Innovation Special Fund(2021THFS0215)。
文摘As Moore’s law deteriorates,the research and development of new materials system are crucial for transitioning into the post Moore era.Traditional semiconductor materials,such as silicon,have served as the cornerstone of modern technologies for over half a century.This has been due to extensive research and engineering on new techniques to continuously enrich silicon-based materials system and,subsequently,to develop better performed silicon-based devices.Meanwhile,in the emerging post Moore era,layered semiconductor materials,such as transition metal dichalcogenides(TMDs),have garnered considerable research interest due to their unique electronic and optoelectronic properties,which hold great promise for powering the new era of next generation electronics.As a result,techniques for engineering the properties of layered semiconductors have expanded the possibilities of layered semiconductor-based devices.However,there remain significant limitations in the synthesis and engineering of layered semiconductors,impeding the utilization of layered semiconductor-based devices for mass applications.As a practical alternative,heterogeneous integration between layered and traditional semiconductors provides valuable opportunities to combine the distinctive properties of layered semiconductors with well-developed traditional semiconductors materials system.Here,we provide an overview of the comparative coherence between layered and traditional semiconductors,starting with TMDs as the representation of layered semiconductors.We highlight the meaningful opportunities presented by the heterogeneous integration of layered semiconductors with traditional semiconductors,representing an optimal strategy poised to propel the emerging semiconductor research community and chip industry towards unprecedented advancements in the coming decades.
基金Project supported by the National Key Research and Development Program of China(Grant No.2022YFB2803900)the National Natural Science Foundation of China(Grant Nos.61704121 and 61974075)+2 种基金Natural Science Foundation of Tianjin City(Grant Nos.19JCQNJC00700 and 22JCZDJC00460)Tianjin Municipal Education Commission(Grant No.2019KJ028)Fundamental Research Funds for the Central Universities(Grant No.22JCZDJC00460)。
文摘In recent years,valleytronics researches based on 2D semiconducting transition metal dichalcogenides have attracted considerable attention.On the one hand,strong spin–orbit interaction allows the presence of spin–valley coupling in this system,which provides spin addressable valley degrees of freedom for information storage and processing.On the other hand,large exciton binding energy up to hundreds of me V enables excitons to be stable carriers of valley information.Valley polarization,marked by an imbalanced exciton population in two inequivalent valleys(+K and-K),is the core of valleytronics as it can be utilized to store binary information.Motivated by the potential applications,we present a thorough overview of the recent advancements in the generation,relaxation,manipulation,and transport of the valley polarization in nonmagnetic transition metal dichalcogenide layered semiconductors.We also discuss the development of valleytronic devices and future challenges in this field.
文摘According to the Fowler theory and numerous experiments the quantum efficiency for photoemission from conductors increases with temperature. Here we show that an opposite temperature dependence is also possible, when the photoemission is from quasi-metallic surface accumulation layers of n-type semiconductors. This is due to the temperature dependence of the Fermi level energy in semiconductors. The Fermi level energy increases with decreasing temperature;this leads to a decrease of the semiconductor work function and consequently an increase of the quantum efficiency photoemission at constant value of absorbed light quanta of energy. We have calculated this effect for electron accumulation layer in n-GaN, induced by adsorption of positively charged cesium or barium ions. It is found that at low temperatures near liquid nitrogen, the quantum efficiency for photoemission increases to near 55%, which is comparable to the largest values, reported for any known photo-ca-thodes. This phenomenon may prove useful for efficient photo-cathodes operating at low temperatures.
基金Supported by the National Key Research and Development Program of China (Grant Nos.2017YFA0403600 and 2016YFA0300404)the National Natural Science Foundation of China (Grant Nos.11874363,11974356 and U1932216)the Collaborative Innovation Program of Hefei Science Center,CAS (Grant No.2019HSC-CIP002)。
文摘Atomically thin two-dimensional(2D) materials are the building bricks for next-generation electronics and optoelectronics, which demand plentiful functional properties in mechanics, transport, magnetism and photoresponse.For electronic devices, not only metals and high-performance semiconductors but also insulators and dielectric materials are highly desirable. Layered structures composed of 2D materials of different properties can be delicately designed as various useful heterojunction or homojunction devices, in which the designs on the same material(namely homojunction) are of special interest because preparation techniques can be greatly simplified and atomically seamless interfaces can be achieved. We demonstrate that the insulating pristine ZnPS_3, a ternary transition-metal phosphorus trichalcogenide, can be transformed into a highly conductive metal and an n-type semiconductor by intercalating Co and Cu atoms, respectively. The field-effect-transistor(FET) devices are prepared via an ultraviolet exposure lithography technique. The Co-ZnPS_3 device exhibits an electrical conductivity of 8 × 10^(4) S/m, which is comparable to the conductivity of graphene. The Cu-ZnPS_3 FET reveals a current ON/OFF ratio of 1-05 and a mobility of 3 × 10^(-2 )cm^(2)·V^(-1)·s^(-1). The realization of an insulator, a typical semiconductor and a metallic state in the same 2D material provides an opportunity to fabricate n-metal homojunctions and other in-plane electronic functional devices.
基金Project supported by the Innovation Program of the Shanghai Institute of Ceramics(Grant No.Y39ZC1110G)the Innovation Program of the Chinese Academy of Sciences(Grant No.KJCX2-EW-W10)+3 种基金the Industry–Academic Joint Technological Innovations Fund Project of Jiangsu Province,China(Grant No.BY2011119)the Natural Science Foundation of Shanghai(Grant No.14ZR1419000)the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.61404146)the National High-tech R&D Program of China(Grant Nos.2013AA031603 and 2014AA032602)
文摘Al-doped ZnO thin film （AZO） is used as a subcontact layer in 6H-SiC photoconductive semiconductor switches （PCSSs） to reduce the on-state resistance and optimize the device structure. Our photoconductive test shows that the onstate resistance of lateral PCSS with an n＋-AZO subcontact layer is 14.7% lower than that of PCSS without an n＋-AZO subcontact layer. This occurs because a heavy-doped AZO thin film can improve Ohmic contact properties, reduce contact resistance, and alleviate Joule heating. Combined with the high transparance characteristic at 532 nm of AZO film, vertical structural PCSS devices are designed and their structural superiority is discussed. This paper provides a feasible route for fabricating high performance SiC PCSS by using conductive and transparent ZnO-based materials.
基金supported by the State Key Project of Fundamental Research of China No.2007CB924903 and NSFC No.50572053
文摘[FeNi（3 nm）/Zn1-xCoxO（3 nm）]2/ZnO（d nm）/[Zn1-xCoxO（3 nm）/Co（3 nm）]2 （d=3 and 10） semiconductor junctions were prepared by magnetron sputtering system and photolithography. The spin valve effect was observed in these junctions because the utility of the ferromagnetic composite layers acted as soft and hard magnetic layers. The electrical detection was performed by measuring the magnetoresistance of these junctions to investigate the current spin polarization asc in the ZnO layer and the spin injection efficiency η of spin-polarized electrons. asc was reduced from 11.7% （and 10.5%） at 90 K to 7.31% （and 5.93%） at room temperature for d=3 （and d=10）. And η was reduced from 39.5% （and 35.5%） at 90 K to 24.7% （and 20.0%） at room temperature for d=3 （and d=10）.
文摘Molecular Beam Epitaxy (MBE) system equipped with in-situ Reflection High-Energy Electron Diffraction (RHEED) has been used for (Ge, Mn) thin film growth and monitoring the surface morphology and crystal structure of thin films. Based on the observation of changes in RHEED patterns during nanocolumn growth, we used a real-time control approach to realize multilayer structures that consist of two nanocolumn layers separated by a Ge barrier layer. Transmission Electron Microscopy (TEM) has been used to investigate the structural properties of the GeMn nanocolumns and GeMn/Ge nanocolumns bi-layers samples.
文摘Accumulation-type GaN metal-oxide-semiconductor field-effect transistors （MOSFETs） with atomic-layer- deposited A1203 gate dielectrics are fabricated. The device, with atomic-layer-deposited A1203 as the gate dielectric, presents a drain current of 260 mA/mm and a broad maximum transconductance of 34 mS/mm, which are better than those reported previously with Al203 as the gate dielectric. Furthermore, the device shows negligible current collapse in a wide range of bias voltages, owing to the effective passivation of the GaN surface by the A1203 film. The gate drain breakdown voltage is found to be about 59.5 V, and in addition the channel mobility of the n-GaN layer is about 380 cm^2/Vs, which is consistent with the Hall result, and it is not degraded by atomic-layer-deposition A1203 growth and device fabrication.
文摘Investigation of the electric properties of semi-conducting materials in an applied ac electric fields gives information about the nature of charge transport and localized states in the forbidden gap. Layered crystals usually contain structural defects, such as dislocations and vacancies that may form a high density of localized states near the Fermi level. So, the current study was carried out for insight into the dielectric Properties of Tl2S layered single crystals. These properties were studied using the ac measurements in the low temperatures ranging from 77 to 300 K. The real part of dielectric constant ε?, imaginary part of dielectric constant ε?, the dissipation factor tan δ and the alternating current conductivity σac were measured in an applied ac electric field of frequencies extending from 2.5 to 50 kHz. Based on the dependencies of these dielectric parameters on both the frequency and temperature, the dielectric properties of the crystals under investigation were elucidated and analyzed. The ac conductivity was found to obey the power law σac(ω) = Aωs with which the values of the exponent s were evaluated to be less than unity in the range 0.21 ≥ s ≥ 0.19. Furthermore, it was found that the temperature dependence of ac conductivity follows the Arrhenius relation via which the impact of temperature on the electrical processes in an applied ac electric field was illustrated and analyzed. The influences of temperature and frequency on both the exponent s and band gap were also discussed in this investigation.
基金Project supported by the National Natural Science Foundation of China(Grant No.42150102)the Sichuan Science and Technology Program(Grant No.2023NSFSC1910)。
文摘Amorphous states of two-dimensional(2D)materials frequently exhibit remarkable physical properties that differ significantly from their crystalline counterparts.Typically,metastable amorphous states can be achieved through rapid quenching from high temperatures.However,the heating process is detrimental to the structural integrity of 2D materials.In this study,we successfully utilized pressure as an external stimulus to induce an amorphous state in layered crystal SiP.Comprehensive experimental and theoretical investigations revealed metallization in the high-pressure amorphous phase of SiP.The recovered samples were characterized using x-ray diffraction,Raman spectroscopy,high-resolution transmission electron microscopy,and selected area electron diffraction.The results indicate that the metallic amorphous SiP obtained under extreme conditions can be stabilized at ambient conditions.These findings provide a viable pathway for inducing metastable phases in 2D materials and offer new insights into the design and development of advanced electronic devices.
基金supported by the National Natural Science Foundation of China(62374037)the Shanghai Municipal Natural Science Foundation(20ZR1403200)the National Young 1000 Talent Plan of China。
文摘Anti-Stokes photoluminescence(ASPL)in low-dimensional van der Waals(vdW)layered materials is becoming increasingly attractive for its potential in advanced applications such as optical cooling,sub-energy band detection and optoelectronic devices.While transition metal dichalcogenides(TMDCs),among the most studied vdW semiconductors for ASPL,exhibit a direct bandgap exclusively in their monolayer form.This characteristic results in a short light-matter interaction distance and thus low ASPL emission efficiency,which seriously impedes the advancement of ASPL in vdW layered materials.In contrast,transition metal halide lead iodide(PbI_(2)),a vdW semiconductor with a direct bandgap in a wide range of thicknesses(⩾3 layers)superior to TMDCs,has shown promise for ASPL.However,the reported ASPL emission efficiency of PbI_(2) is notably low.Moreover,scant research has focused on the rich ASPL emission states in PbI_(2),particularly concerning the assignment of these emission states.Here,through a designed thickness selection,we observed more detailed ASPL emissions in submicrometer-thick PbI_(2) at room temperature,in addition to a series of previously unreported ASPL emission peaks that emerge at low temperatures.Importantly,the low-temperature ASPL of PbI_(2) exhibits an approximate 1000-fold enhancement compared to that observed at room temperature.This significant enhancement is attributed to the transition from phonon-assisted one-photon absorption to two-step photon absorption induced by resonance absorption effect,as well as substantially reduced nonradiative decays at low temperatures.Our findings enhance the comprehensive understanding of ASPL in PbI_(2),holding great significance for the development of ASPL applications.
