Ohmic contacts are fundamental components in semiconductor technology,facilitating efficient electrical connection and excellent device performance.We employ first-principles calculations to show that semimetallic gra...Ohmic contacts are fundamental components in semiconductor technology,facilitating efficient electrical connection and excellent device performance.We employ first-principles calculations to show that semimetallic graphene is a natural Ohmic contact partner of monolayer semiconducting black arsenic(BAs),for which the top of the valence band is below the Fermi energy of the order of 10~2 meV.The Ohmic contact arises from the giant Stark effect induced by van der Waals electron transfer from BAs to graphene,which does not destroy their respective band features.Remarkably,we show that this intrinsic Ohmic contact remains robust across a wide range of interlayer distances(adjustable by strain)or vertical electric fields,whereas the weak spin splitting of the order of 1 meV induced by symmetry breaking plays little part in Ohmic contact.These findings reveal the potential applications of graphene–BAs in ultralow dissipation transistors.展开更多
The design of customized crystal plane heterojunction can effectively leverage the optimal anisotropic interaction of crystal plane,thereby enhancing photocatalytic activity.In this study,Co_(3)O_(4) exposed(111),(110...The design of customized crystal plane heterojunction can effectively leverage the optimal anisotropic interaction of crystal plane,thereby enhancing photocatalytic activity.In this study,Co_(3)O_(4) exposed(111),(110),and(100)crystal planes(designated as HCO,NCO,and CCO,respectively)were synthesized and successfully coupled with Cd_(0.5)Zn_(0.5)S(CZS).Among these composites,the HCO/CZS exhibited best hydrogen evolution activity.In conjunction with DFT calculations and femtosecond transient absorption spectroscopy,it has been found that:the crystal plane interaction between HCO and CZS enabled the composite catalyst to exhibit optimal anisotropy in crystal plane carrier transport,crystal plane active sites,and crystal plane electronic structure.This interaction induces a redistribution of electrons at their contact interface,thereby establishing a built-in electric field that facilitates the formation of ohmic heterojunction between HCO and CZS.The synergistic effect of the ohmic heterojunction and crystal plane anisotropy not only decreases the Gibbs free energy of hydrogen adsorption but also facilitates the efficient spatial separation and rapid transfer of electron-hole pairs.This study offers valuable insights into the customization of crystal plane heterojunctions,aiming to maximize anisotropic interactions between crystal planes in order to enhance photocatalytic hydrogen evolution.展开更多
The ohmic contact interface between diamond and metal is essential for the application of diamond detectors.Surface modification can significantly affect the contact performance and eliminate the interface polarizatio...The ohmic contact interface between diamond and metal is essential for the application of diamond detectors.Surface modification can significantly affect the contact performance and eliminate the interface polarization effect.However,the radiation stability of a diamond detector is also sensitive to surface modification.In this work,the influence of surface modification technology on a diamond ohmic contact under high-energy radiation was investigated.Before radiation,the specific contact resistivities(ρc)between Ti/Pt/Au-hydrogen-terminated diamond(H-diamond)and Ti/Pt/Au-oxygenterminated diamond(O-diamond)were 2.0×10^(-4)W·cm^(2) and 4.3×10^(-3)Wcm^(2),respectively.After 10 MeV electron radiation,the ρc of Ti/Pt/Au H-diamond and Ti/Pt/Au O-diamond were 5.3×10^(-3)W·cm^(2)and 9.1×10^(-3)W·cm^(2),respectively.The rates of change of ρc of H-diamond and O-diamond after radiation were 2550%and 112%,respectively.The electron radiation promotes bond reconstruction of the diamond surface,resulting in an increase in ρc.展开更多
Adjusting the interfacial transport efficiency of photogenerated electrons and the free energy of hydrogen adsorption through interface engineering is an effective means of improving the photocatalytic activity of sem...Adjusting the interfacial transport efficiency of photogenerated electrons and the free energy of hydrogen adsorption through interface engineering is an effective means of improving the photocatalytic activity of semiconductor photocatalysts.Herein,hollow ZnS/NiS nanocages with ohmic contacts containing Zn vacancy(V_(Zn)-ZnS/NiS)are synthesized using ZIF-8 as templates.An internal electric field is constructed by Fermi level flattening to form ohmic contacts,which increase donor density and accelerate electron transport at the V_(Zn)-ZnS/NiS interface.The experimental and DFT results show that the tight interface and V_(Zn) can rearrange electrons,resulting in a higher charge density at the interface,and optimizing the Gibbs free energy of hydrogen adsorption.The optimal hydrogen production activity of V_(Zn)-ZnS/NiS is 10,636 μmol h^(-1) g^(-1),which is 31.9 times that of V_(Zn)-ZnS.This study provides an idea for constructing sulfide heterojunctions with ohmic contacts and defects to achieve efficient photocatalytic hydrogen production.展开更多
Low-resistance Ohmic contact is critical for the high efficiency GaN-based laser diodes.This study investigates the introduction of the In_(0.15)Ga_(0.85)N contact layer on the specific contact resistance.Experimental...Low-resistance Ohmic contact is critical for the high efficiency GaN-based laser diodes.This study investigates the introduction of the In_(0.15)Ga_(0.85)N contact layer on the specific contact resistance.Experimental results reveal that adopting the In0.15Ga0.85N contact layer yields a minimized specific contact resistance of 2.57×10^(-5)Ω·cm^(2) which is two orders of magnitude lower than the GaN contact layer(7.61×10^(-3)Ω·cm^(2)).A decrease in the specific contact resistance arises from the reduction of the barrier between the metal and p-type In0.15Ga0.85N.To develop an optimal metal electrode combination on the In0.15Ga0.85N contact layer,the Pd/Au and Ni/Au electrode stacks which are most commonly used in the formation of Ohmic contact with p-GaN are investigated.Metal stack of 10/30 nm Pd/Au is demonstrated effective in reducing the specific contact resistance to 10^(-5)Ω·cm^(2) level.The mechanism of the variation of the specific contact resistance under different annealing atmospheres is explained by auger electron spectroscopy.展开更多
Motivated by the widespread applications of nanofluids,a nanofluid model is proposed which focuses on uniform magnetohydrodynamic(MHD)boundary layer flow over a non-linear stretching sheet,incorporating the Casson mod...Motivated by the widespread applications of nanofluids,a nanofluid model is proposed which focuses on uniform magnetohydrodynamic(MHD)boundary layer flow over a non-linear stretching sheet,incorporating the Casson model for blood-based nanofluid while accounting for viscous and Ohmic dissipation effects under the cases of Constant Surface Temperature(CST)and Prescribed Surface Temperature(PST).The study employs a two-phase model for the nanofluid,coupled with thermophoresis and Brownian motion,to analyze the effects of key fluid parameters such as thermophoresis,Brownian motion,slip velocity,Schmidt number,Eckert number,magnetic parameter,and non-linear stretching parameter on the velocity,concentration,and temperature profiles of the nanofluid.The proposed model is novel as it simultaneously considers the impact of thermophoresis and Brownian motion,along with Ohmic and viscous dissipation effects,in both CST and PST scenarios for blood-based Casson nanofluid.The numerical technique built into MATLAB’s bvp4c module is utilized to solve the governing system of coupled differential equations,revealing that the concentration of nanoparticles decreases with increasing thermophoresis and Brownian motion parameters while the temperature of the nanofluid increases.Additionally,a higher Eckert number is found to reduce the nanofluid temperature.A comparative analysis between CST and PST scenarios is also undertaken,which highlights the significant influence of these factors on the fluid’s characteristics.The findings have potential applications in biomedical processes to enhance fluid velocity and heat transfer rates,ultimately improving patient outcomes.展开更多
The formation of low-resistance Ohmic contacts in Ga_(2)O_(3) is crucial for high-performance electronic devices. Conventionally, a titanium/gold(Ti/Au) electrode is rapidly annealed to achieve Ohmic contacts, resulti...The formation of low-resistance Ohmic contacts in Ga_(2)O_(3) is crucial for high-performance electronic devices. Conventionally, a titanium/gold(Ti/Au) electrode is rapidly annealed to achieve Ohmic contacts, resulting in mutual diffusion of atoms at the interface. However, the specific role of diffusing elements in Ohmic contact formation remains unclear.In this work, we investigate the contribution of oxygen atom diffusion to the formation of Ohmic contacts in Ga_(2)O_(3). We prepare a Ti/Au electrode on a single crystal substrate and conduct a series of electrical and structural characterizations.Using density functional theory, we construct a model of the interface and calculate the charge density, partial density of states, planar electrostatic potential energy, and I–V characteristics. Our results demonstrate that the oxygen atom diffusion effectively reduces the interface barrier, leading to low-resistance Ohmic contacts in Ga_(2)O_(3). These findings provide valuable insights into the underlying mechanisms of Ohmic contact formation and highlight the importance of considering the oxygen atom diffusion in the design of Ga_(2)O_(3)-based electronic devices.展开更多
Photogenerated charge separation is a challenging step in semiconductor-based photosynthesis.Though numerous efforts have been devoted to developing multi-component photocatalyst heterostructures for improving charge ...Photogenerated charge separation is a challenging step in semiconductor-based photosynthesis.Though numerous efforts have been devoted to developing multi-component photocatalyst heterostructures for improving charge separation efficiency,the short distance between electrons and holes-aggregated regions still leads to undesirable charge recombination.Herein,a facile and commercial in-situ synthesis method was designed to directly prepare a three-component Au–carbon–TiO_(2)photocatalyst from Ti_(3)C_(2)MXene,air,CO_(2),and HAuCl_(4),in which the carbon layer bridged Au and TiO_(2)nanoparticles for stable and efficient photocatalytic hydrogen production.Kelvin probe measurements and density functional theory(DFT)calculations demonstrated that a multi-interfacial charge transmission network was successfully constructed to achieve a directional and long-distance spatial charge separation/transfer channel between TiO_(2)and Au through carbon layer,desirably inhibiting the recombination of photogenerated charge carriers.The hydrogen production rate of the formed three-component Au/C–TiO_(2)(CTA)photocatalyst was demonstrated to be 27 times higher than that of Au–TiO_(2),which also surpassed many reported Ti_(3)C_(2)MXene-derived carbon–TiO_(2)photocatalysts.This work sheds light on the ingenious use of 2D MXene to form a well-behaved TiO_(2)-based photocatalytic system and helps to propose future design principles in accelerating charge transfer.展开更多
The effective separation ability of photogenerated carriers plays a crucial role in catalytic hydrogen production.Establishing a heterojunction structure is an effective means to overcome the limited carrier separatio...The effective separation ability of photogenerated carriers plays a crucial role in catalytic hydrogen production.Establishing a heterojunction structure is an effective means to overcome the limited carrier separation ability of some single catalysts.In this paper,Cu,graphdiyne(GDY)and NiCoMoO_(4)are successfully coupled to construct a composite photocatalyst NCY-15%.The addition of sheet GDY effectively prevents the aggregation of NiCoMoO_(4),increases the number of active sites,and enhances the light-trapping ability of the composite catalyst.The synergistic interaction of S-scheme heterojunction and Ohmic junction heterojunction between Cu,GDY and NiCoMoO_(4)provides a unique transfer pathway for electrons,facilitating the rapid separation of photogenerated carriers and accelerating electron transfer,while retaining electrons with strong reducing capacity to participate in hydrogen production,thereby increasing the hydrogen evolution rate.This provides a new way for the development of GDY based photocatalysts.展开更多
The present investigation centers on the impact of viscous dissipation and ohmic heating on the plume generated by a line heat source under the impact of an aligned magnetic field.In this study,the flow model is adapt...The present investigation centers on the impact of viscous dissipation and ohmic heating on the plume generated by a line heat source under the impact of an aligned magnetic field.In this study,the flow model is adapted to incorporate ohmic heating and viscous dissipation by including the respective terms in the energy equation.A mathematical model is formulated as a system of coupled partial differential equations to analyze the flow problem.Subsequently,a numerical solution is derived with stream function formulation for the system of coupled partial differential equations,which transmutes it into ordinary differential equations.To achieve this,the numerical properties of the problem are established through the utilization of the Shooting method in tandem with the MATLAB tool bvp4c.The graphical representations of both missing and specified boundary conditions depict the effects of the magnetic parameter,viscous dissipation variable,magnetic force parameter,Prandtl number,and magnetic Prandtl number.These are accompanied by a discussion of their respective physical implications.The observed results claimed that the velocity,current density,and temperature distribution decrease for enhancing magnetic parameters.Meanwhile,the skin friction and magnetic flux drop while the heat transfer rate increases with an increment in magnetic parameters.These fluid flow and heat transfer characteristics were observed to decrease for increasing viscous dissipation.The current work is novel in incorporating ohmic heating viscous dissipation in energy equations coupled with Max-well and magnetic induction equations.展开更多
N-wells are created by P＋ ion implantation into Si-faced p-type 4H-SiC epilayer. Ti and Ni are deposited in sequence on the surface of the active regions. Ni2Si is identified as the dominant phase by X-ray diffracti...N-wells are created by P＋ ion implantation into Si-faced p-type 4H-SiC epilayer. Ti and Ni are deposited in sequence on the surface of the active regions. Ni2Si is identified as the dominant phase by X-ray diffraction （XRD） analysis after metallization annealing. An amorphous C film at the Ni2 Si/SiC interface is confirmed by an X-ray energy-dispersive spectrometer （XEDS）. The Ni2Si and amorphous C film are etched away selectively,followed by deposition of new metal films without annealing. Measurement of the current-voltage characteristics shows that the contacts are still ohmic after the Ni2 Si and amorphous C film are replaced by new metal films. The sheet resistance Rsh of the implanted layers decreases from 975 to 438f2/D, because carbon vacancies （Vc） appeared during annealing,which act as donors for electrons in SiC.展开更多
Polysilicon ohmic contacts to n-type 4H-SiC have been fabricated. TLM （transfer length method） test patterns with polysilicon structure are formed on n-wells created by phosphorus ion （P^＋） implantation into a Si...Polysilicon ohmic contacts to n-type 4H-SiC have been fabricated. TLM （transfer length method） test patterns with polysilicon structure are formed on n-wells created by phosphorus ion （P^＋） implantation into a Si-faced p-type 4H-SiC epilayer. The polysilicon is deposited using low-pressure chemical vapor deposition （LPCVD） and doped by phosphorous ions implantation followed by diffusion to obtain a sheet resistance of 22Ω/□. The specific contact resistance pc of n^＋ polysilicon contact to n-type 4H-SiC as low as 3.82 × 10^-5Ω· cm^2 is achieved. The result for sheet resistance Rsh of the phosphorous ion implanted layers in SiC is about 4.9kΩ/□. The mechanisms for n^＋ polysilicon ohmic contact to n-type SiC are discussed.展开更多
An investigation of Au/Ti/Ni and Au/Ti/Pt ohmic contacts to n-type 4H-SiC and the behavior of metal films on SiC with thermal anneals is reported. Specific contact resistance as low as 2. 765 x 10^-6Ω·cm^2 was a...An investigation of Au/Ti/Ni and Au/Ti/Pt ohmic contacts to n-type 4H-SiC and the behavior of metal films on SiC with thermal anneals is reported. Specific contact resistance as low as 2. 765 x 10^-6Ω·cm^2 was achieved after rapid thermal annealing in N2 for 2min at 950℃. SIMS analysis shows that the formation of Ni silicide after annealing supported a number of carbon atoms＇ outdiffusion from the SiC to form interstitial compound TiC. This process can create abundant C vacancies near the interface. It is the carbon defect layer that enhances the defect-assisted tunneling. The interface band structure within the defect level could make it clear why the metal-SiC contacts become ohmic during annealing.展开更多
A novel structure of ideal ohmic contact p^＋ （SiGeC）-n^- -n^＋ diodes with three-step graded doping concentration in the base region is presented, and the changing doping concentration gradient is also optimized. U...A novel structure of ideal ohmic contact p^＋ （SiGeC）-n^- -n^＋ diodes with three-step graded doping concentration in the base region is presented, and the changing doping concentration gradient is also optimized. Using MEDICI, the physical parameter models applicable for SiGeC/Si heterojunction power diodes are given. The simulation results indicate that the diodes with graded doping concentration in the base region not only have the merit of fast and soft reverse recovery but also double reverse blocking voltage,and their forward conducting voltage has dropped to some extent,compared to the diodes with constant doping concentration in the base region. The new structure achieves a good trade-off in Qs-Vf-Ir ,and its combination of properties is superior to ideal ohmic contact diodes and conventional diodes.展开更多
A pre-ohmic micro-patterned recess process,is utilized to fabricate Ti/Al/Ti/TiN ohmic contact to an ultrathin-barrier(UTB)AlGaN/GaN heterostructure,featuring a significantly reduced ohmic contact resistivity of 0.56...A pre-ohmic micro-patterned recess process,is utilized to fabricate Ti/Al/Ti/TiN ohmic contact to an ultrathin-barrier(UTB)AlGaN/GaN heterostructure,featuring a significantly reduced ohmic contact resistivity of 0.56Ω·mm at an alloy temperature of 550℃.The sheet resistances increase with the temperature following a power law with the index of +2.58,while the specific contact resistivity decreases with the temperature.The contact mechanism can be well described by thermionic field emission(TFE).The extracted Schottky barrier height and electron concentration are 0.31 eV and 5.52×10^(18) cm^(−3),which suggests an intimate contact between ohmic metal and the UTB-AlGaN as well as GaN buffer.A good correlation between ohmic transfer length and the micro-pattern size is revealed,though in-depth investigation is needed.A preliminary CMOS-process-compatible metal-insulator-semiconductor high-mobility transistor(MIS-HEMT)was fabricated with the proposed Au-free ohmic contact technique.展开更多
Ohmic losses of a coaxial cavity gyrotron with outer corrugation are investigated.The results show that the averaged ohmic loss densities of the inner and outer conductors have similar changes along with the axial dir...Ohmic losses of a coaxial cavity gyrotron with outer corrugation are investigated.The results show that the averaged ohmic loss densities of the inner and outer conductors have similar changes along with the axial direction of the gyrotron;whereas averaged ohmic loss densities of the outer conductor are more than the inner conductor;the outer slot depth and width cause greatly the averaged ohmic loss densities of the corrugation bottom and the corrugation period of outer conductor,and averaged densities of ohmic losses on the inner conductor are almost unaffected.展开更多
Ohmic Heating (OH) is one of the emerging thermal technologies used in food processing which can produce rapid and uniform heating with close to 100% energy transfer efficiency. Although mathematical </span><...Ohmic Heating (OH) is one of the emerging thermal technologies used in food processing which can produce rapid and uniform heating with close to 100% energy transfer efficiency. Although mathematical </span><span style="font-family:Verdana;">modelling</span><span style="font-family:Verdana;"> for OH processes has been studied by many researchers in recent years, systematic simulations of OH have not been developed for model-based control of the processes. In this paper, </span><span style="font-family:Verdana;">mathematical</span><span style="font-family:Verdana;"> model for a Colinear Ohmic Heater is presented, analyzed, and studied based on the selected configuration. A numerical solution for the mathematical equations has been defined and proposed. MATLAB/Simulink model is hence developed and validated against the available data. Simulation results have shown that </span><span style="font-family:Verdana;">MATLAB</span><span style="font-family:Verdana;">/Simulink model can produce robust outputs at low computational costs with an accuracy of up to 99.6% in comparison to the analytical solution. This model can be used in further studies for analysis of the OH processes and development of advanced controllers.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.62374088 and 12074193)。
文摘Ohmic contacts are fundamental components in semiconductor technology,facilitating efficient electrical connection and excellent device performance.We employ first-principles calculations to show that semimetallic graphene is a natural Ohmic contact partner of monolayer semiconducting black arsenic(BAs),for which the top of the valence band is below the Fermi energy of the order of 10~2 meV.The Ohmic contact arises from the giant Stark effect induced by van der Waals electron transfer from BAs to graphene,which does not destroy their respective band features.Remarkably,we show that this intrinsic Ohmic contact remains robust across a wide range of interlayer distances(adjustable by strain)or vertical electric fields,whereas the weak spin splitting of the order of 1 meV induced by symmetry breaking plays little part in Ohmic contact.These findings reveal the potential applications of graphene–BAs in ultralow dissipation transistors.
文摘The design of customized crystal plane heterojunction can effectively leverage the optimal anisotropic interaction of crystal plane,thereby enhancing photocatalytic activity.In this study,Co_(3)O_(4) exposed(111),(110),and(100)crystal planes(designated as HCO,NCO,and CCO,respectively)were synthesized and successfully coupled with Cd_(0.5)Zn_(0.5)S(CZS).Among these composites,the HCO/CZS exhibited best hydrogen evolution activity.In conjunction with DFT calculations and femtosecond transient absorption spectroscopy,it has been found that:the crystal plane interaction between HCO and CZS enabled the composite catalyst to exhibit optimal anisotropy in crystal plane carrier transport,crystal plane active sites,and crystal plane electronic structure.This interaction induces a redistribution of electrons at their contact interface,thereby establishing a built-in electric field that facilitates the formation of ohmic heterojunction between HCO and CZS.The synergistic effect of the ohmic heterojunction and crystal plane anisotropy not only decreases the Gibbs free energy of hydrogen adsorption but also facilitates the efficient spatial separation and rapid transfer of electron-hole pairs.This study offers valuable insights into the customization of crystal plane heterojunctions,aiming to maximize anisotropic interactions between crystal planes in order to enhance photocatalytic hydrogen evolution.
基金Project supported by the National Key Research and Development Program of China(Grant No.2022YFB3608601).
文摘The ohmic contact interface between diamond and metal is essential for the application of diamond detectors.Surface modification can significantly affect the contact performance and eliminate the interface polarization effect.However,the radiation stability of a diamond detector is also sensitive to surface modification.In this work,the influence of surface modification technology on a diamond ohmic contact under high-energy radiation was investigated.Before radiation,the specific contact resistivities(ρc)between Ti/Pt/Au-hydrogen-terminated diamond(H-diamond)and Ti/Pt/Au-oxygenterminated diamond(O-diamond)were 2.0×10^(-4)W·cm^(2) and 4.3×10^(-3)Wcm^(2),respectively.After 10 MeV electron radiation,the ρc of Ti/Pt/Au H-diamond and Ti/Pt/Au O-diamond were 5.3×10^(-3)W·cm^(2)and 9.1×10^(-3)W·cm^(2),respectively.The rates of change of ρc of H-diamond and O-diamond after radiation were 2550%and 112%,respectively.The electron radiation promotes bond reconstruction of the diamond surface,resulting in an increase in ρc.
基金financially supported by the Natural National Science Foundation of China(22178084)the Natural Science Foundation for Distinguished Young Scholars of Hebei Province(No.B2015208010)+2 种基金Fundamental Research Funds for the Central Universitiesthe Foundation for Innovative Research Groups of the Natural Science Foundation of Hebei Province(No.B2021208005)National Key R&D Program of China(2022YFE0101800).
文摘Adjusting the interfacial transport efficiency of photogenerated electrons and the free energy of hydrogen adsorption through interface engineering is an effective means of improving the photocatalytic activity of semiconductor photocatalysts.Herein,hollow ZnS/NiS nanocages with ohmic contacts containing Zn vacancy(V_(Zn)-ZnS/NiS)are synthesized using ZIF-8 as templates.An internal electric field is constructed by Fermi level flattening to form ohmic contacts,which increase donor density and accelerate electron transport at the V_(Zn)-ZnS/NiS interface.The experimental and DFT results show that the tight interface and V_(Zn) can rearrange electrons,resulting in a higher charge density at the interface,and optimizing the Gibbs free energy of hydrogen adsorption.The optimal hydrogen production activity of V_(Zn)-ZnS/NiS is 10,636 μmol h^(-1) g^(-1),which is 31.9 times that of V_(Zn)-ZnS.This study provides an idea for constructing sulfide heterojunctions with ohmic contacts and defects to achieve efficient photocatalytic hydrogen production.
基金funded by the Natural Science Foundation of China Project,grant number 62274042Natural Science Foundation of Shanghai,grant number 21ZR1406200the Key Research and Development Program of Jiangsu Province,grant number BE2021008-5.
文摘Low-resistance Ohmic contact is critical for the high efficiency GaN-based laser diodes.This study investigates the introduction of the In_(0.15)Ga_(0.85)N contact layer on the specific contact resistance.Experimental results reveal that adopting the In0.15Ga0.85N contact layer yields a minimized specific contact resistance of 2.57×10^(-5)Ω·cm^(2) which is two orders of magnitude lower than the GaN contact layer(7.61×10^(-3)Ω·cm^(2)).A decrease in the specific contact resistance arises from the reduction of the barrier between the metal and p-type In0.15Ga0.85N.To develop an optimal metal electrode combination on the In0.15Ga0.85N contact layer,the Pd/Au and Ni/Au electrode stacks which are most commonly used in the formation of Ohmic contact with p-GaN are investigated.Metal stack of 10/30 nm Pd/Au is demonstrated effective in reducing the specific contact resistance to 10^(-5)Ω·cm^(2) level.The mechanism of the variation of the specific contact resistance under different annealing atmospheres is explained by auger electron spectroscopy.
基金funded by Universiti Teknikal Malaysia Melaka and Ministry of Higher Education(MoHE)Malaysia,grant number FRGS/1/2024/FTKM/F00586.
文摘Motivated by the widespread applications of nanofluids,a nanofluid model is proposed which focuses on uniform magnetohydrodynamic(MHD)boundary layer flow over a non-linear stretching sheet,incorporating the Casson model for blood-based nanofluid while accounting for viscous and Ohmic dissipation effects under the cases of Constant Surface Temperature(CST)and Prescribed Surface Temperature(PST).The study employs a two-phase model for the nanofluid,coupled with thermophoresis and Brownian motion,to analyze the effects of key fluid parameters such as thermophoresis,Brownian motion,slip velocity,Schmidt number,Eckert number,magnetic parameter,and non-linear stretching parameter on the velocity,concentration,and temperature profiles of the nanofluid.The proposed model is novel as it simultaneously considers the impact of thermophoresis and Brownian motion,along with Ohmic and viscous dissipation effects,in both CST and PST scenarios for blood-based Casson nanofluid.The numerical technique built into MATLAB’s bvp4c module is utilized to solve the governing system of coupled differential equations,revealing that the concentration of nanoparticles decreases with increasing thermophoresis and Brownian motion parameters while the temperature of the nanofluid increases.Additionally,a higher Eckert number is found to reduce the nanofluid temperature.A comparative analysis between CST and PST scenarios is also undertaken,which highlights the significant influence of these factors on the fluid’s characteristics.The findings have potential applications in biomedical processes to enhance fluid velocity and heat transfer rates,ultimately improving patient outcomes.
基金Projects supported by the National Natural Science Foundation of China (Grant Nos.61874084,61974119,and U21A20501)。
文摘The formation of low-resistance Ohmic contacts in Ga_(2)O_(3) is crucial for high-performance electronic devices. Conventionally, a titanium/gold(Ti/Au) electrode is rapidly annealed to achieve Ohmic contacts, resulting in mutual diffusion of atoms at the interface. However, the specific role of diffusing elements in Ohmic contact formation remains unclear.In this work, we investigate the contribution of oxygen atom diffusion to the formation of Ohmic contacts in Ga_(2)O_(3). We prepare a Ti/Au electrode on a single crystal substrate and conduct a series of electrical and structural characterizations.Using density functional theory, we construct a model of the interface and calculate the charge density, partial density of states, planar electrostatic potential energy, and I–V characteristics. Our results demonstrate that the oxygen atom diffusion effectively reduces the interface barrier, leading to low-resistance Ohmic contacts in Ga_(2)O_(3). These findings provide valuable insights into the underlying mechanisms of Ohmic contact formation and highlight the importance of considering the oxygen atom diffusion in the design of Ga_(2)O_(3)-based electronic devices.
基金supported by the National Natural Science Foundation of China(No.21972171)the Fundamental Research Funds for the Central Universities,South-Central MinZu University(Nos.CZQ23037,CZY23018)+1 种基金the Hubei Provincial Natural Science Foundation,China(No.2021CFA022)the Innovation and Entrepreneurship Training Program Funded by South-Central Minzu University(No.S202310524033).
文摘Photogenerated charge separation is a challenging step in semiconductor-based photosynthesis.Though numerous efforts have been devoted to developing multi-component photocatalyst heterostructures for improving charge separation efficiency,the short distance between electrons and holes-aggregated regions still leads to undesirable charge recombination.Herein,a facile and commercial in-situ synthesis method was designed to directly prepare a three-component Au–carbon–TiO_(2)photocatalyst from Ti_(3)C_(2)MXene,air,CO_(2),and HAuCl_(4),in which the carbon layer bridged Au and TiO_(2)nanoparticles for stable and efficient photocatalytic hydrogen production.Kelvin probe measurements and density functional theory(DFT)calculations demonstrated that a multi-interfacial charge transmission network was successfully constructed to achieve a directional and long-distance spatial charge separation/transfer channel between TiO_(2)and Au through carbon layer,desirably inhibiting the recombination of photogenerated charge carriers.The hydrogen production rate of the formed three-component Au/C–TiO_(2)(CTA)photocatalyst was demonstrated to be 27 times higher than that of Au–TiO_(2),which also surpassed many reported Ti_(3)C_(2)MXene-derived carbon–TiO_(2)photocatalysts.This work sheds light on the ingenious use of 2D MXene to form a well-behaved TiO_(2)-based photocatalytic system and helps to propose future design principles in accelerating charge transfer.
基金supported by the Innovative Team for Transforming Waste Cooking Oil into Clean Energy and High Value-Added Chemicals(2022QCXTD03)Ningxia low-grade resource high value utilization and environmental chemical integration technology innovation team project,and Ningxia Natural Science Foundation of 2022(Outstanding Youth Project),Project number:2022AAC05034.
文摘The effective separation ability of photogenerated carriers plays a crucial role in catalytic hydrogen production.Establishing a heterojunction structure is an effective means to overcome the limited carrier separation ability of some single catalysts.In this paper,Cu,graphdiyne(GDY)and NiCoMoO_(4)are successfully coupled to construct a composite photocatalyst NCY-15%.The addition of sheet GDY effectively prevents the aggregation of NiCoMoO_(4),increases the number of active sites,and enhances the light-trapping ability of the composite catalyst.The synergistic interaction of S-scheme heterojunction and Ohmic junction heterojunction between Cu,GDY and NiCoMoO_(4)provides a unique transfer pathway for electrons,facilitating the rapid separation of photogenerated carriers and accelerating electron transfer,while retaining electrons with strong reducing capacity to participate in hydrogen production,thereby increasing the hydrogen evolution rate.This provides a new way for the development of GDY based photocatalysts.
基金supported by the National Foreign Expert Project-Foreign Youth Talent Program Fund No.QN2023001001Beijing Natural Science Foundation Project-Foreign Scholar Program Fund No.IS23046/ZW001A00202301+1 种基金National Natural Science Foundation of China(NSFC)Fund No.12202019Beijing PostdoctoralResearch Activities Fund No.Q6001A00202301.
文摘The present investigation centers on the impact of viscous dissipation and ohmic heating on the plume generated by a line heat source under the impact of an aligned magnetic field.In this study,the flow model is adapted to incorporate ohmic heating and viscous dissipation by including the respective terms in the energy equation.A mathematical model is formulated as a system of coupled partial differential equations to analyze the flow problem.Subsequently,a numerical solution is derived with stream function formulation for the system of coupled partial differential equations,which transmutes it into ordinary differential equations.To achieve this,the numerical properties of the problem are established through the utilization of the Shooting method in tandem with the MATLAB tool bvp4c.The graphical representations of both missing and specified boundary conditions depict the effects of the magnetic parameter,viscous dissipation variable,magnetic force parameter,Prandtl number,and magnetic Prandtl number.These are accompanied by a discussion of their respective physical implications.The observed results claimed that the velocity,current density,and temperature distribution decrease for enhancing magnetic parameters.Meanwhile,the skin friction and magnetic flux drop while the heat transfer rate increases with an increment in magnetic parameters.These fluid flow and heat transfer characteristics were observed to decrease for increasing viscous dissipation.The current work is novel in incorporating ohmic heating viscous dissipation in energy equations coupled with Max-well and magnetic induction equations.
文摘N-wells are created by P＋ ion implantation into Si-faced p-type 4H-SiC epilayer. Ti and Ni are deposited in sequence on the surface of the active regions. Ni2Si is identified as the dominant phase by X-ray diffraction （XRD） analysis after metallization annealing. An amorphous C film at the Ni2 Si/SiC interface is confirmed by an X-ray energy-dispersive spectrometer （XEDS）. The Ni2Si and amorphous C film are etched away selectively,followed by deposition of new metal films without annealing. Measurement of the current-voltage characteristics shows that the contacts are still ohmic after the Ni2 Si and amorphous C film are replaced by new metal films. The sheet resistance Rsh of the implanted layers decreases from 975 to 438f2/D, because carbon vacancies （Vc） appeared during annealing,which act as donors for electrons in SiC.
文摘Polysilicon ohmic contacts to n-type 4H-SiC have been fabricated. TLM （transfer length method） test patterns with polysilicon structure are formed on n-wells created by phosphorus ion （P^＋） implantation into a Si-faced p-type 4H-SiC epilayer. The polysilicon is deposited using low-pressure chemical vapor deposition （LPCVD） and doped by phosphorous ions implantation followed by diffusion to obtain a sheet resistance of 22Ω/□. The specific contact resistance pc of n^＋ polysilicon contact to n-type 4H-SiC as low as 3.82 × 10^-5Ω· cm^2 is achieved. The result for sheet resistance Rsh of the phosphorous ion implanted layers in SiC is about 4.9kΩ/□. The mechanisms for n^＋ polysilicon ohmic contact to n-type SiC are discussed.
文摘An investigation of Au/Ti/Ni and Au/Ti/Pt ohmic contacts to n-type 4H-SiC and the behavior of metal films on SiC with thermal anneals is reported. Specific contact resistance as low as 2. 765 x 10^-6Ω·cm^2 was achieved after rapid thermal annealing in N2 for 2min at 950℃. SIMS analysis shows that the formation of Ni silicide after annealing supported a number of carbon atoms＇ outdiffusion from the SiC to form interstitial compound TiC. This process can create abundant C vacancies near the interface. It is the carbon defect layer that enhances the defect-assisted tunneling. The interface band structure within the defect level could make it clear why the metal-SiC contacts become ohmic during annealing.
文摘A novel structure of ideal ohmic contact p^＋ （SiGeC）-n^- -n^＋ diodes with three-step graded doping concentration in the base region is presented, and the changing doping concentration gradient is also optimized. Using MEDICI, the physical parameter models applicable for SiGeC/Si heterojunction power diodes are given. The simulation results indicate that the diodes with graded doping concentration in the base region not only have the merit of fast and soft reverse recovery but also double reverse blocking voltage,and their forward conducting voltage has dropped to some extent,compared to the diodes with constant doping concentration in the base region. The new structure achieves a good trade-off in Qs-Vf-Ir ,and its combination of properties is superior to ideal ohmic contact diodes and conventional diodes.
基金supported by National Natural Science Foundation of China under Grant 61822407,Grant 62074161,and Grant 11634002in part by the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(CAS)under Grant QYZDB-SSW-JSC012+3 种基金in part by the National Key Research and Development Program of China under Grant 2016YFB0400105 and Grant 2017YFB0403000in part by the Youth Innovation Promotion Association of CASin part by the University of Chinese Academy of Sciencesand in part by the Opening Project of Key Laboratory of Microelectronic Devices&Integrated Technology,Institute of Microelectronics,CAS.
文摘A pre-ohmic micro-patterned recess process,is utilized to fabricate Ti/Al/Ti/TiN ohmic contact to an ultrathin-barrier(UTB)AlGaN/GaN heterostructure,featuring a significantly reduced ohmic contact resistivity of 0.56Ω·mm at an alloy temperature of 550℃.The sheet resistances increase with the temperature following a power law with the index of +2.58,while the specific contact resistivity decreases with the temperature.The contact mechanism can be well described by thermionic field emission(TFE).The extracted Schottky barrier height and electron concentration are 0.31 eV and 5.52×10^(18) cm^(−3),which suggests an intimate contact between ohmic metal and the UTB-AlGaN as well as GaN buffer.A good correlation between ohmic transfer length and the micro-pattern size is revealed,though in-depth investigation is needed.A preliminary CMOS-process-compatible metal-insulator-semiconductor high-mobility transistor(MIS-HEMT)was fabricated with the proposed Au-free ohmic contact technique.
基金Supported by the Scientific Research Foundation of Sichuan Provincal Department of Education under Grant No 10ZC059。
文摘Ohmic losses of a coaxial cavity gyrotron with outer corrugation are investigated.The results show that the averaged ohmic loss densities of the inner and outer conductors have similar changes along with the axial direction of the gyrotron;whereas averaged ohmic loss densities of the outer conductor are more than the inner conductor;the outer slot depth and width cause greatly the averaged ohmic loss densities of the corrugation bottom and the corrugation period of outer conductor,and averaged densities of ohmic losses on the inner conductor are almost unaffected.
文摘Ohmic Heating (OH) is one of the emerging thermal technologies used in food processing which can produce rapid and uniform heating with close to 100% energy transfer efficiency. Although mathematical </span><span style="font-family:Verdana;">modelling</span><span style="font-family:Verdana;"> for OH processes has been studied by many researchers in recent years, systematic simulations of OH have not been developed for model-based control of the processes. In this paper, </span><span style="font-family:Verdana;">mathematical</span><span style="font-family:Verdana;"> model for a Colinear Ohmic Heater is presented, analyzed, and studied based on the selected configuration. A numerical solution for the mathematical equations has been defined and proposed. MATLAB/Simulink model is hence developed and validated against the available data. Simulation results have shown that </span><span style="font-family:Verdana;">MATLAB</span><span style="font-family:Verdana;">/Simulink model can produce robust outputs at low computational costs with an accuracy of up to 99.6% in comparison to the analytical solution. This model can be used in further studies for analysis of the OH processes and development of advanced controllers.
