Quantum confinement effects and source-to-drain tunneling in ultra-scaled double-gate silicon n-MOSFETs

By using the linear combination of bulk band (LCBB) method incorporated with the top of the barrier splitting (TBS) model, we present a comprehensive study on the quantum confinement effects and the source-to-drain tunneling in the ultra-scaled double-gate (DG) metal-oxide-semiconductor field-effect transistors (MOSFETs). A critical body thickness value of 5 nm is found, below which severe valley splittings among different X valleys for the occupied charge density and the current contributions occur in ultra-thin silicon body structures. It is also found that the tunneling current could be nearly 100% with an ultra-scaled channel length. Different from the previous simulation results, it is found that the source-to-drain tunneling could be effectively suppressed in the ultra-thin body thickness (2.0 nm and below) by the quantum confinement and the tunneling could be suppressed down to below 5% when the channel length approaches 16 nm regardless of the body thickness.     

Light-modulated electron retroreflection and Klein tunneling in a graphene-based n-p-n junction

We investigate the electron retroreflection and the Klein tunneling across a graphene-based n-p-n junction irradiated by linearly polarized off-resonant light with the polarization along the x direction. The linearly polarized off-resonant light modifies the band structure of graphene, which leads to the anisotropy of band structure. By adjusting the linearly polarized light and the direction of n-p-n junction simultaneously, the electron retroreflection appears and the anomalous Klein tunneling, the perfect transmission at a nonzero incident angle regardless of the width and height of potential barrier, happens, which arises from the fact that the light-induced anisotropic band structure changes the relation of wavevector and velocity of electron. Our finding provides an alternative and flexible method to modulate electron retroreflection and Klein tunneling.     

偏压在隧道效应中的作用

从隧道扫描势垒模型出发。用量子力学导出隧道电流与针尖间的偏压、间距及它们的逸出功之间的关系,并从能带模型的角度导出样品与针尖的间距不变时,隧道电流与偏压成正比关系．指出偏压的作用主要是提高针尖上电子的能量,使针尖上的电子比样品上的电子更容易穿过势垒,从而形成隧道电流．     

薄膜电致发光器件中SiO2层加速机制的研究

研究非晶SiO2缺陷能级上电子的隧道效应,移植实验的XPS芯能级谱技术,用DV-Xα计算界面SiO2/ZnS的能带断错,认为该界面处的能带断错是电子加速的主要机制.     

Two-dimensional threshold voltage model of a nanoscale silicon-on-insulator tunneling field-effect transistor

The tunneling field-effect transistor(TFET) is a potential candidate for the post-CMOS era.In this paper,a threshold voltage model is developed for this new kind of device.First,two-dimensional(2D) models are used to describe the distributions of potential and electric field in the channel and two depletion regions.Then based on the physical definition of threshold voltage for the nanoscale TFET,the threshold voltage model is developed.The accuracy of the proposed model is verified by comparing the calculated results with the 2D device simulation data.It has been demonstrated that the effects of varying the device parameters can easily be investigated using the model presented in this paper.This threshold voltage model provides a valuable reference to TFET device design,simulation,and fabrication.     

Two-dimensional threshold voltage model of nanoscale silicon-on-insulator tunneling field-effect transistor

The tunneling field-effect transistor (TFET) is a potential candidate for the post-CMOS era. In this paper, a threshold voltage model is developed for this new kind of device. First, two-dimensional (2D) models are used to describe the distributions of potential and electric field in the channel and two depletion regions. Then based on the physical definition of threshold voltage for the nanoscale TFET, the threshold voltage model is developed. The accuracy of the proposed model is verified by comparing the calculated results with the 2D device simulation data. It has been demonstrated that the effects of varying the device parameters can easily be investigated using the model presented in this paper. This threshold voltage model provides a valuable reference to the TFET device design, simulation, and fabrication.     

STS investigations of temperature dependence of Au(1 1 1) surface state energy position

High temperature scanning tunneling spectroscopy (HT-STS) was used to investigate the electronic structure of Au(1 1 1) at different temperatures in the energy range 0-1 eV below the Fermi level. We concentrated on the influence of temperature on the Shockley surface state (SS) appearing on noble metals surface due to a surface projected bulk bang gap in [1 1 1] direction. The influence of temperature on the projected band gap edge (BE) was also investigated. The experiment was carried out in the temperature range 294-580 K. As the result of the experiment a delicate shift of the SS and the BE in direction of the Fermi level was reported.     

Cross-sectional scanning tunneling microscopy and spectroscopy of strain in buried heterostructure lasers

Cross-sectional scanning tunneling microscopy and spectroscopy have been used to probe the unreconstructed (1 1 0) surface of a commercially available buried heterostructure laser in ultra high vacuum. Complex re-growth above the non-linear blocking layers is shown to induce tensile strain in the device. Spectroscopic measurements show an increase in both the density of filled valence band states and empty conduction band states as a result of the strain, with a particularly large increase at −3.1 V. Current imaging tunneling spectroscopy measurements show an increase in the tunneling current in to and out of the strained regions at both gap voltage polarities, consistent with the spectroscopy. Moving towards tensile strain, InP is known to maintain much the same bandgap, with the split-off level and lower lying states being drawn up towards the valence band edge, consistent with the data.     

Hopping motion of chlorine atoms on Si(1 0 0)-(2 × 1) surfaces induced by carrier injection from scanning tunneling microscope tips

Injection of tunneling electrons and holes from the probe tips of a scanning tunneling microscope was found to enhance the hopping motion of Cl atoms between neighboring dangling-bond sites of Si dimers on Si(1 0 0)-(2 × 1) surfaces, featured by the rate of hopping linearly dependent on the injection current. The hopping rate formed peaks at sample biases of V_S∼+1.25 and −0.85 V, which agree with the peaks in the local density of states spectrum measured by scanning tunneling spectroscopy. The Cl hopping was enhanced at Cl-adsorbed sites even remote from the injection point. The Cl hopping by hole injection was more efficiently enhanced by sweeping the tip along the Si dimer row than by tip-sweeping along the perpendicular direction. Such anisotropy, on the other hand, was insignificant in the electron injection case. All of these findings can be interpreted by the model that the holes injected primarily into a surface band originated from the dangling bonds of Si dimers propagate quite anisotropically along the surface, and become localized at Cl sites somehow to destabilize the Si-Cl bonds causing hopping of the Cl atoms. The electrons injected into a bulk band propagate in an isotropic manner and then get resonantly trapped at Si-Cl antibonding orbitals, resulting in bond destabilization and hopping of the Cl atoms.     

Three-dimensional Wentzel–Kramers–Brillouin approach for the simulation of scanning tunneling microscopy and spectroscopy

We review the recently developed three-dimensional (3D) atom-superposition approach for simulating scanning tunneling microscopy (STM) and spectroscopy (STS) based on ab initio electronic structure data. In the method, contributions from individual electron tunneling transitions between the tip apex atom and each of the sample surface atoms are summed up assuming the one-dimensional (1D) Wentzel–Kramers–Brillouin (WKB) approximation in all these transitions. This 3D WKB tunneling model is extremely suitable to simulate spin-polarized STM and STS on surfaces exhibiting a complex noncollinear magnetic structure, i.e., without a global spin quantization axis, at very low computational cost. The tip electronic structure from first principles can also be incorporated into the model, that is often assumed to be constant in energy in the vast majority of the related literature, which could lead to a misinterpretation of experimental findings. Using this approach, we highlight some of the electron tunneling features on a prototype frustrated hexagonal antiferromagnetic Cr monolayer on Ag(111) surface. We obtain useful theoretical insights into the simulated quantities that is expected to help the correct evaluation of experimental results. By extending the method to incorporate a simple orbital dependent electron tunneling transmission, we reinvestigate the bias voltage- and tip-dependent contrast inversion effect on theW(110) surface. STM images calculated using this orbital dependent model agree reasonably well with Tersoff-Hamann and Bardeen results. The computational efficiency of the model is remarkable as the k-point samplings of the surface and tip Brillouin zones do not affect the computational time, in contrast to the Bardeen method. In a certain case we obtain a relative computational time gain of 8500 compared to the Bardeen calculation, without the loss of quality. We discuss the advantages and limitations of the 3D WKB method, and show further ways to improve and extend it.     

铁磁-p波超导结中的自旋极化隧道谱与散粒噪声

考虑到界面的势垒散射和铁磁层中的磁交换作用，依照Sr2RuO4超导体具有自旋三重配对态的p波对称结构，研究铁磁-p波超导结中的自旋极化隧道谱与散粒噪声，研究表明：1.对于幺正配对态，随着铁磁层中磁交换劈裂增强，隧道谱与散粒噪声都减少；2.对于非幺正配对态，隧道谱与散粒噪声都依赖于铁磁层的磁化轴方向，当磁化轴平行于非幺正配对态的自旋轴时，在低偏压下磁交换作用能使隧谱与散粒噪声增强，而当磁化轴反平行于自旋转轴时，其结果相反。     

A prospective: Quantitative scanning tunneling spectroscopy of semiconductor surfaces

Analysis methods that enable quantitative energies of states to be obtained from vacuum tunneling spectra of semiconductors are discussed. The analysis deals with the problem of tip-induced band bending in the semiconductor, which distorts the voltage-scale of the spectra so that it does not correspond directly to energy values. Three-dimensional electrostatic modeling is used to solve the electrostatics of the tip-vacuum-semiconductor system, and an approximate (semiclassical in the radial direction) solution for the wavefunctions is used to obtain the tunnel current. Various applications of the method to semiconductor surfaces and other material systems are discussed, and possible extensions of the method are considered.     

隧道场效应晶体管静电放电冲击特性研究

随着器件尺寸的不断减小,集成度的逐步提高,功耗成为了制约集成电路产业界发展的主要问题之一.由于通过引入带带隧穿机理可以实现更小的亚阈值斜率,隧道场效应晶体管(TFET)器件已成为下一代集成电路的最具竞争力的备选器件之一.但是TFET器件更薄的栅氧化层、更短的沟道长度容易使器件局部产生高的电流密度、电场密度和热量,使得其更容易遭受静电放电(ESD)冲击损伤.此外,TFET器件基于带带隧穿机理的全新工作原理也使得其ESD保护设计面临更多挑战.本文采用传输线脉冲的ESD测试方法深入分析了基本TFET器件在ESD冲击下器件开启、维持、泄放和击穿等过程的电流特性和工作机理.在此基础之上,给出了一种改进型TFET抗ESD冲击器件,通过在源端增加N型高掺杂区,有效的调节接触势垒形状,降低隧穿结的宽度,从而获得更好的ESD设计窗口.     

(001)面任意方向单轴应变硅材料能带结构

首先计算了(001)晶面单轴应变张量,在此基础上采用结合形变势理论的K ·P微扰法建立了在(001)晶面内受任意方向的单轴压/张应力作用时,应变硅材料的能带结构与应力(类型、大小)及晶向的关系模型,进而分析了不同单轴应力(类型、大小)及晶向对应变硅材料导带带边、价带带边、导带分裂能、价带分裂能、禁带宽度的影响.研究结果可为单轴应变硅器件应力及晶向的选择设计提供理论依据. 关键词： 单轴应变硅 K ·P法 能带结构     

Desorption of chlorine atoms on Si (1 1 1)-(7 × 7) surfaces induced by hole injection from scanning tunneling microscope tips

We investigated desorption of chlorine atoms on Si (1 1 1)-(7 × 7) surfaces induced by hole injection from scanning tunneling microscope tips. The hole-induced desorption of chlorine atoms had a threshold bias voltage corresponding to the energy position of the S3 surface band originated in Si backbonds. The chlorine atom desorption rate was almost proportional to the square of the tunneling current. We have discussed possible mechanisms that two holes injected into Si surface states get localized at the backbonds of chlorinated Si adatoms, which induces the rupture of Cl-Si bonds to result in chlorine atom desorption.     

Transition from zero-dimensional to one-dimensional behavior in InAs and CdSe nanorods

Tunneling and optical spectroscopy performed on InAs nanorods 7–25 nm long, reveal a clear dependence of the band gap on length. This (zero-dimension like) behavior is different from that of CdSe rods, where the band gap is nearly independent of length, a signature of quasi-one-dimensionality. The transition between these two regimes is governed by the ratio between the Bohr radius and the nanorods length. The gaps measured by tunneling spectroscopy are larger than the optical gaps by a factor that depends on the tunneling configuration. This is attributed to a combination of the Coulomb interaction and the voltage division between the two tunnel junctions in the STM experiment. However, the tunneling gaps were found to reduce in dense aggregates of rods.     

Realization of semiconducting Cu2Se by direct selenization of Cu(111)

Bulk group IB transition-metal chalcogenides have been widely explored due to their applications in thermoelectrics. However, a layered two-dimensional form of these materials has been rarely reported. Here, we realize semiconducting Cu₂Se by direct selenization of Cu(111). Scanning tunneling microcopy measurements combined with first-principles calculations allow us to determine the structural and electronic properties of the obtained structure. X-ray photoelectron spectroscopy data reveal chemical composition of the sample, which is Cu₂Se. The observed moiré pattern indicates a lattice mismatch between Cu₂Se and the underlying Cu(111)-$\sqrt{3}$×$\sqrt{3}$ surface. Differential conductivity obtained by scanning tunneling spectroscopy demonstrates that the synthesized Cu₂Se exhibits a band gap of 0.78 eV. Furthermore, the calculated density of states and band structure demonstrate that the isolated Cu₂Se is a semiconductor with an indirect band gap of ～ 0.8 eV, which agrees quite well with the experimental results. Our study provides a simple pathway varying toward the synthesis of novel layered 2D transition chalcogenides materials.     

Observation of the screened potential and the Friedel oscillation by low-temperature scanning tunneling microscopy/spectroscopy

Using low-temperature scanning tunneling microscopy/spectroscopy we have developed a method for measuring electrostatic potential in high spatial and energy resolutions, and performed a real-space observation of the potential screened by two-dimensional surface electrons around step edges, where extra charges are localized, on the Si(1 1 1)√3 × √3-Ag surface. In the potential images, characteristic decay and the Friedel oscillation were clearly observed around the charges.     

High temperature scanning tunneling microscopy of purely ion conducting yttria stabilized zirconia (YSZ)

Scanning tunneling microscopy (STM) on wide band gap insulators is generally not possible. Here we demonstrate that ionic insulators with high ion mobility, such as yttria stabilized zirconia, are an exception to this rule. The ion conductivity ensures that the sample maintains a defined potential relative to the STM tip and thus a stable tunnel junction. Consequently, ion conductors provide an opportunity for characterizing wide band gap insulators, and thin films and nanostructures supported on them by STM.