A theoretical study on discrete vortex bound states is carried out near a vortex core in the presence of a van Hove singularity(VHS) near the Fermi level by solving Bogoliubov–de Gennes(Bd G) equations. When the VHS ...A theoretical study on discrete vortex bound states is carried out near a vortex core in the presence of a van Hove singularity(VHS) near the Fermi level by solving Bogoliubov–de Gennes(Bd G) equations. When the VHS lies exactly at the Fermi level and also at the middle of the band, a zero-energy state and other higher-energy states whose energy ratios follow integer numbers emerge. These discrete vortex bound state peaks undergo a splitting behavior when the VHS or Fermi level moves away from the middle of the band. Such splitting behavior will eventually lead to a new arrangement of quantized vortex core states whose energy ratios follow half-odd-integer numbers.展开更多
The dependences of Fermi-level pinning on interface state densities for the metal-dielectric, ploycrystalline silicon-dielectric, and metal silicide-dielectric interfaces are investigated by calculating their effectiv...The dependences of Fermi-level pinning on interface state densities for the metal-dielectric, ploycrystalline silicon-dielectric, and metal silicide-dielectric interfaces are investigated by calculating their effective work functions and their pinning factors. The Fermi-level pinning factors and effective work functions of the metal-dielectric interface are observed to be more susceptible to the increasing interface state densities, differing significantly from that of the ploycrystalline silicon-dielectric interface and the metal silicide-dielectric interface. The calculation results indicate that metal silicide gates with high-temperature resistance and low resistivity are a more promising choice for the design of gate materials in metal-oxide semiconductor（MOS） technology.展开更多
Superconducting SnTe-type topological crystalline insulators(TCIs)are predicted to host multiple Majorana zero modes(MZMs)which can coexist in a single vortex.Fermi level(FL)close to the Dirac points of topological su...Superconducting SnTe-type topological crystalline insulators(TCIs)are predicted to host multiple Majorana zero modes(MZMs)which can coexist in a single vortex.Fermi level(FL)close to the Dirac points of topological surface states is helpful for detecting MZMs.However,the TCI SnTe is a heavily p-type semiconductor which is very difficult to modify to n-type via doping or alloying.In this work,we fabricate the atomically flat Sn_(1-x)Pb_(x)Te/Pb heterostructure by molecular beam epitaxy,and make the p-type Sn_(1-x)Pb_(x)Te become n-type through changing the interface roughness.Using scanning tunnelling microscope,we find the Dirac points of Sn_(1-x)Pb_(x)Te/Pb heterostructure are always above the FL due to the Fermi level pinning(FLP)induced by topological surface states at atomically flat interface.After increasing the interface roughness,the FLP effect is suppressed and then the Dirac points of p-type Sn_(1-x)Pb_(x)Te can be tuned very close to or even below the FL.Our work provides a new method for tuning the FL of SnTe-type TCI which has potential application in novel topological superconductor device.展开更多
We present a generic approximate graphical method for determining the equilibrium Fermi level and majority carrier density of a semiconductor with multiple donors and multiple acceptors compensating each other. Simple...We present a generic approximate graphical method for determining the equilibrium Fermi level and majority carrier density of a semiconductor with multiple donors and multiple acceptors compensating each other. Simple and easy-to-follow procedures of the graphical method are described.By graphically plotting two wrapping step functions facing each other,one for the positive hole-ionized donor and one for the negative electron-ionized acceptor,we have the crossing point that renders the Fermi level and majority carrier density.Using the graphical method,new equations are derived,such as the carrier compensation proportional to N;/N;,not the widely quoted N;-N;.Visual insight is offered to view not only the result of graphic determination of Fermi level and majority carrier density but also the dominant and critical pair of donors and acceptors in compensation.The graphical method presented in this work will help to guide the design,adjustment,and improvement of the multiply doped semiconductors.Comparison of this approximate graphical method with previous work on compensation,and with some experimental results,is made.Future work in the field is proposed.展开更多
The photocatalytic performances are highly dependent on the charge separation and surface reaction kinetics of photocatalysts.Aiming at figuring out the effects of co-catalyst with the lower Fermi level on photocataly...The photocatalytic performances are highly dependent on the charge separation and surface reaction kinetics of photocatalysts.Aiming at figuring out the effects of co-catalyst with the lower Fermi level on photocatalytic activity,we tuned the Fermi level of Pt nanoparticles on g-C_(3)N_(4)(GCN)by introducing Co atom.Experimental results show that lowering the Fermi level of co-catalyst does not alter light absorption of GCN due to the invariable structure.Besides,Pt_(3)Co with a lower Fermi level contributes less positive influence on charge separation in GCN due to an opposite effect from the stronger electron-trap ability of Pt_(3)Co and increased band bending in GCN-Pt_(3)Co.The density functional theory(DFT)calculations indicate that GCN-Pt_(3)Co has faster surface reaction kinetics than GCN-Pt,owing to easier dissociation of H_(2)O molecules and faster desorption of H^(*)on Pt_(3)Co.Consequently,GCN-Pt_(3)Co exhibits an excellent H_(2) evolution rate with 2.91 mmol g^(-1)·h^(-1),which 2.67 times that of GCN-Pt.展开更多
For semiconductors with localized intrinsic/impurity defects, intentionally doped or unintentionally incorporated, that have multiple transition energy levels among charge states, the general formulation of the local ...For semiconductors with localized intrinsic/impurity defects, intentionally doped or unintentionally incorporated, that have multiple transition energy levels among charge states, the general formulation of the local charge neutrality condition is given for the determination of the Fermi level and the majority carrier density. A graphical method is used to illustrate the solution of the problem. Relations among the transition energy levels of the multi-level defect are derived using the graphical method. Numerical examples are given for p-doping of the CdTe thin film used in solar panels and semi-insulating Si to illustrate the relevance and importance of the issues discussed in this work.展开更多
A compact model is proposed to derive the charge density of the AlInSb/InSb HEMT devices by con- sidering the variation of Fermi level, the first subband, the second subband and sheet carrier charge density with appli...A compact model is proposed to derive the charge density of the AlInSb/InSb HEMT devices by con- sidering the variation of Fermi level, the first subband, the second subband and sheet carrier charge density with applied gate voltage. The proposed model considers the Fermi level dependence of charge density and vice versa. The analytical results generated by the proposed model are compared and they agree well with the experimental results. The developed model can be used to implement a physics based compact model for an InSb HEMT device in SPICE applications.展开更多
Insertion of a C-containing layer in a metal/Ge structure,using a chemical bath,enabled the Schottky barrier height（SBH） to be modulated.Chemical baths with 1-octadecene,1-hexadecene,1-tetradecene,and 1- dodecene we...Insertion of a C-containing layer in a metal/Ge structure,using a chemical bath,enabled the Schottky barrier height（SBH） to be modulated.Chemical baths with 1-octadecene,1-hexadecene,1-tetradecene,and 1- dodecene were used separately with Ge substrates.An ultrathin C-containing layer stops the penetration of free electron wave functions from the metal to the Ge.Metal-induced gap states are alleviated and the pinned Fermi level is released.The SBH is lowered to 0.17 eV.This new formation method is much less complex than traditional ones,and the result is very good.展开更多
Fermi level pinning and interface instability have hindered the achievement of field-effect-transistors(FETs)with high performance.Interface passivation and doping engineering technology have become the main driving f...Fermi level pinning and interface instability have hindered the achievement of field-effect-transistors(FETs)with high performance.Interface passivation and doping engineering technology have become the main driving force to solve the issue.Herein,interface chemistry and transport characteristics determination of Hf_(1-x)Yb_(x)O_(y)/Al_(2)O_(3)/GaSb gate stacks have been achieved by passivation and doping process.X-ray photoelectron spectroscopy characterization and electrical measurements have demonstrated the existence of less intrinsic oxides and elemental Sb at Hf_(1-x)Yb_(x)O_(y)/Al_(2)O_(3)/GaSb interface with optimized doping content,as well as the minimum leakage current density of 2.23×10^(5)A cm.The energy distribution of interface state based on conductance method has confirmed the achievement of the lowest interface state density of 1.98×10^(13)e Vcm,resulting in Fermi level unpinning.Carrier transport mechanisms of Hf_(1-x)Yb_(x)O_(y)/Al_(2)O_(3)/GaSb MOS capacitors as a function of temperature have been investigated systematically and some important electrical parameters have been extracted.Comprehensive analyses show that sputtering-derived Hf_(1-x)Yb_(x)O_(y)/Al_(2)O_(3)/GaSb(x=0.32)gate stack has potential application in future Ga Sbbased metal-oxide-semiconductor field effect transistor(MOSFET)devices.展开更多
The widely used deep level transient spectroscopy（DLTS） theory and data analysis usually assume that the defect level distribution is uniform through the depth of the depletion region of the n–p junction. In this w...The widely used deep level transient spectroscopy（DLTS） theory and data analysis usually assume that the defect level distribution is uniform through the depth of the depletion region of the n–p junction. In this work we introduce the concept of effective Fermi level of the steady state of semiconductor, by using which deep level transient spectroscopy depth profiling（DLTSDP） is proposed. Based on the relationship of its transition free energy level（TFEL） and the effective Fermi level, the rules of detectivity of the defect levels are listed. Computer simulation of DLTSDP is presented and compared with experimental data. The experimental DLTS data are compared with what the DLTSDP selection rules predicted. The agreement is satisfactory.展开更多
Electron spectrum in doped n-Si quantum wires is calculated by the Thomas-Fermi (TF) method under finite temperatures. The many-body exchange corrections are taken into account. The doping profile is arbitrary. At the...Electron spectrum in doped n-Si quantum wires is calculated by the Thomas-Fermi (TF) method under finite temperatures. The many-body exchange corrections are taken into account. The doping profile is arbitrary. At the first stage, the electron potential energy is calculated from a simple two-dimensional equation. The effective iteration scheme is proposed there that is valid for multidimensional problems. Then the energy levels and wave functions of this quantum well are simulated from the Schrödinger equations. The expansion by the full set of eigenfunctions of the linear harmonic oscillator is used. The quantum mechanical perturbation theory can be utilized to compute the energy levels. Generally, the perturbation theory for degenerate energy levels should be used.展开更多
基金the National Natural Science Foundation of China (Grant No. 11804154)the Scientific Research Foundation of NJIT (Grant Nos. YKJ201853 and CKJA201807)。
文摘A theoretical study on discrete vortex bound states is carried out near a vortex core in the presence of a van Hove singularity(VHS) near the Fermi level by solving Bogoliubov–de Gennes(Bd G) equations. When the VHS lies exactly at the Fermi level and also at the middle of the band, a zero-energy state and other higher-energy states whose energy ratios follow integer numbers emerge. These discrete vortex bound state peaks undergo a splitting behavior when the VHS or Fermi level moves away from the middle of the band. Such splitting behavior will eventually lead to a new arrangement of quantized vortex core states whose energy ratios follow half-odd-integer numbers.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61376096,61327813,and 11234007)
文摘The dependences of Fermi-level pinning on interface state densities for the metal-dielectric, ploycrystalline silicon-dielectric, and metal silicide-dielectric interfaces are investigated by calculating their effective work functions and their pinning factors. The Fermi-level pinning factors and effective work functions of the metal-dielectric interface are observed to be more susceptible to the increasing interface state densities, differing significantly from that of the ploycrystalline silicon-dielectric interface and the metal silicide-dielectric interface. The calculation results indicate that metal silicide gates with high-temperature resistance and low resistivity are a more promising choice for the design of gate materials in metal-oxide semiconductor（MOS） technology.
基金the Ministry of Science and Technology of China(Grant Nos.2019YFA0308600,and 2020YFA0309000)the National Natural Science Foundation of China(Grant Nos.11861161003,12104293,92365302,22325203,92265105,92065201,12074247,and 12174252)+3 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB28000000)the Science and Technology Commission of Shanghai Municipality(Grant Nos.2019SHZDZX01,19JC1412701,and 20QA1405100)the Innovation program for Quantum Science and Technology(Grant No.2021ZD0302500)the China National Postdoctoral Program for Innovative Talents(Grant No.BX2021185)。
文摘Superconducting SnTe-type topological crystalline insulators(TCIs)are predicted to host multiple Majorana zero modes(MZMs)which can coexist in a single vortex.Fermi level(FL)close to the Dirac points of topological surface states is helpful for detecting MZMs.However,the TCI SnTe is a heavily p-type semiconductor which is very difficult to modify to n-type via doping or alloying.In this work,we fabricate the atomically flat Sn_(1-x)Pb_(x)Te/Pb heterostructure by molecular beam epitaxy,and make the p-type Sn_(1-x)Pb_(x)Te become n-type through changing the interface roughness.Using scanning tunnelling microscope,we find the Dirac points of Sn_(1-x)Pb_(x)Te/Pb heterostructure are always above the FL due to the Fermi level pinning(FLP)induced by topological surface states at atomically flat interface.After increasing the interface roughness,the FLP effect is suppressed and then the Dirac points of p-type Sn_(1-x)Pb_(x)Te can be tuned very close to or even below the FL.Our work provides a new method for tuning the FL of SnTe-type TCI which has potential application in novel topological superconductor device.
文摘We present a generic approximate graphical method for determining the equilibrium Fermi level and majority carrier density of a semiconductor with multiple donors and multiple acceptors compensating each other. Simple and easy-to-follow procedures of the graphical method are described.By graphically plotting two wrapping step functions facing each other,one for the positive hole-ionized donor and one for the negative electron-ionized acceptor,we have the crossing point that renders the Fermi level and majority carrier density.Using the graphical method,new equations are derived,such as the carrier compensation proportional to N;/N;,not the widely quoted N;-N;.Visual insight is offered to view not only the result of graphic determination of Fermi level and majority carrier density but also the dominant and critical pair of donors and acceptors in compensation.The graphical method presented in this work will help to guide the design,adjustment,and improvement of the multiply doped semiconductors.Comparison of this approximate graphical method with previous work on compensation,and with some experimental results,is made.Future work in the field is proposed.
基金supported by the National Key Research and Development Program of China(No.2017YFE0193900)the National Natural Science Foundation of China(No.51802255)+4 种基金the Natural Science Foundation of Shaanxi Province(Nos.2021GXLH-Z-O and 2020JZ-02)the project of Innovative Team of Shaanxi Province(2020TD-001)the China Fundamental Research Funds for the Central Universitiesthe World-Class Universities(Disciplines)the Characteristic Development Guidance Funds for the Central Universities.
文摘The photocatalytic performances are highly dependent on the charge separation and surface reaction kinetics of photocatalysts.Aiming at figuring out the effects of co-catalyst with the lower Fermi level on photocatalytic activity,we tuned the Fermi level of Pt nanoparticles on g-C_(3)N_(4)(GCN)by introducing Co atom.Experimental results show that lowering the Fermi level of co-catalyst does not alter light absorption of GCN due to the invariable structure.Besides,Pt_(3)Co with a lower Fermi level contributes less positive influence on charge separation in GCN due to an opposite effect from the stronger electron-trap ability of Pt_(3)Co and increased band bending in GCN-Pt_(3)Co.The density functional theory(DFT)calculations indicate that GCN-Pt_(3)Co has faster surface reaction kinetics than GCN-Pt,owing to easier dissociation of H_(2)O molecules and faster desorption of H^(*)on Pt_(3)Co.Consequently,GCN-Pt_(3)Co exhibits an excellent H_(2) evolution rate with 2.91 mmol g^(-1)·h^(-1),which 2.67 times that of GCN-Pt.
文摘For semiconductors with localized intrinsic/impurity defects, intentionally doped or unintentionally incorporated, that have multiple transition energy levels among charge states, the general formulation of the local charge neutrality condition is given for the determination of the Fermi level and the majority carrier density. A graphical method is used to illustrate the solution of the problem. Relations among the transition energy levels of the multi-level defect are derived using the graphical method. Numerical examples are given for p-doping of the CdTe thin film used in solar panels and semi-insulating Si to illustrate the relevance and importance of the issues discussed in this work.
基金Project supported by the Council of Scientific & Industrial Research(CSIR),India under the Senior Research Fellowship Scheme(No.08/237(0005)/2012-EMR-I)
文摘A compact model is proposed to derive the charge density of the AlInSb/InSb HEMT devices by con- sidering the variation of Fermi level, the first subband, the second subband and sheet carrier charge density with applied gate voltage. The proposed model considers the Fermi level dependence of charge density and vice versa. The analytical results generated by the proposed model are compared and they agree well with the experimental results. The developed model can be used to implement a physics based compact model for an InSb HEMT device in SPICE applications.
基金supported by the Chinese National Key Basic Research Program(No.2011CBA00602)the National Key Scientific and Technological Projects,China(Nos.2009ZX02035-004-02,2011ZX02708-002)
文摘Insertion of a C-containing layer in a metal/Ge structure,using a chemical bath,enabled the Schottky barrier height（SBH） to be modulated.Chemical baths with 1-octadecene,1-hexadecene,1-tetradecene,and 1- dodecene were used separately with Ge substrates.An ultrathin C-containing layer stops the penetration of free electron wave functions from the metal to the Ge.Metal-induced gap states are alleviated and the pinned Fermi level is released.The SBH is lowered to 0.17 eV.This new formation method is much less complex than traditional ones,and the result is very good.
基金the National Natural Science Foundation of China(No.11774001)the Anhui Project(No.Z010118169)。
文摘Fermi level pinning and interface instability have hindered the achievement of field-effect-transistors(FETs)with high performance.Interface passivation and doping engineering technology have become the main driving force to solve the issue.Herein,interface chemistry and transport characteristics determination of Hf_(1-x)Yb_(x)O_(y)/Al_(2)O_(3)/GaSb gate stacks have been achieved by passivation and doping process.X-ray photoelectron spectroscopy characterization and electrical measurements have demonstrated the existence of less intrinsic oxides and elemental Sb at Hf_(1-x)Yb_(x)O_(y)/Al_(2)O_(3)/GaSb interface with optimized doping content,as well as the minimum leakage current density of 2.23×10^(5)A cm.The energy distribution of interface state based on conductance method has confirmed the achievement of the lowest interface state density of 1.98×10^(13)e Vcm,resulting in Fermi level unpinning.Carrier transport mechanisms of Hf_(1-x)Yb_(x)O_(y)/Al_(2)O_(3)/GaSb MOS capacitors as a function of temperature have been investigated systematically and some important electrical parameters have been extracted.Comprehensive analyses show that sputtering-derived Hf_(1-x)Yb_(x)O_(y)/Al_(2)O_(3)/GaSb(x=0.32)gate stack has potential application in future Ga Sbbased metal-oxide-semiconductor field effect transistor(MOSFET)devices.
基金the China Triumph International Engineering Company (CTIEC), Shanghai, China, which offered generous financial support for this work
文摘The widely used deep level transient spectroscopy（DLTS） theory and data analysis usually assume that the defect level distribution is uniform through the depth of the depletion region of the n–p junction. In this work we introduce the concept of effective Fermi level of the steady state of semiconductor, by using which deep level transient spectroscopy depth profiling（DLTSDP） is proposed. Based on the relationship of its transition free energy level（TFEL） and the effective Fermi level, the rules of detectivity of the defect levels are listed. Computer simulation of DLTSDP is presented and compared with experimental data. The experimental DLTS data are compared with what the DLTSDP selection rules predicted. The agreement is satisfactory.
文摘Electron spectrum in doped n-Si quantum wires is calculated by the Thomas-Fermi (TF) method under finite temperatures. The many-body exchange corrections are taken into account. The doping profile is arbitrary. At the first stage, the electron potential energy is calculated from a simple two-dimensional equation. The effective iteration scheme is proposed there that is valid for multidimensional problems. Then the energy levels and wave functions of this quantum well are simulated from the Schrödinger equations. The expansion by the full set of eigenfunctions of the linear harmonic oscillator is used. The quantum mechanical perturbation theory can be utilized to compute the energy levels. Generally, the perturbation theory for degenerate energy levels should be used.
