Observation of Resonant Photon Tunneling in Photonic Double Barrier Structures

Reflectance and transmittance of 632.8 nm He-Ne laser light for photonic double barrier structures (consisting of a SF10 prism, SiO₂ layer, Al or Al₂O₃ active layer, SiO₂ layer and SF10 prism) were measured as a function of the angle of incidence for both the ρ- and s-polarized incidence. Sharp reflection dips and transmission peaks were observed at angles larger than the critical angle of total reflection. The appearance of the transmission peaks can be attributed to resonant photon tunneling through the photonic double barrier structures analogous to resonant electron tunneling through double potential barrier structures. Resonant tunneling is mediated by the long-range surface plasmon polariton in the case of the Al active layer and the electromagnetic guided modes in the case of the Al₂O₃ layer.This paper was originally presented at the seventh Meeting on Near Field Optics, which was held on July 1, 1998 at Nagoya University, Nagoya, organized by Research Group on Near Field Optics, the Optical Society of Japan, an affiliate of Japan Society of Applied Physics. The authors have won the Near Field Optics Award for their best presentation at the meeting.     

Photon assisted tunneling from aluminum into silicon dioxide

Using argon and krypton lasers the photon assisted tunneling of electrons from aluminum into the SiO₂ conduction band was observed for the first time. The data are found to be in excellent agreement with a simple model assuming an AlSiO₂ barrier height of 3.15 eV and an electron effective mass in the SiO₂ band-gap of 0.5m. The results are consistent with the conclusion that the classical image force barrier lowering does not contribute to tunneling. The technique is promising for the study of interface phenomena.     

铁氧化物中电子隧道现象的扫描隧道显微术研究

报道了利用扫描隧道显微术(STM)对金属表面氧化物层进行电子隧道谱研究的结果。在对两类铁晶体表面氧化层进行的隧道谱和势垒高度测量结果进行分析后表明,常温条件下形成的氧化层(Ⅰ类)应主要是Fe₃O₄;而在高温氧化条件下形成的表面层(Ⅱ类)的主要成分则应是Fe₂O₃。从而表明(STM)可用于研究铁表面氧化过程的不同阶段,并且由Ⅰ类氧化层的低势垒特性说明STM还可以用于观测此类氧化层的内部结构。类似研究方法还可应用到对一系列 关键词：     

Features of electronic transport in relaxed Si/Si1−XGeX heterostructures with high doping level

The low-temperature electrical and magnetotransport characteristics of partially relaxed Si/Si_1−xGe_x heterostructures with two-dimensional electron channel (n_e≥10¹² cm⁻²) in an elastically strained silicon layer of nanometer thickness have been studied. The detailed calculation of the potential and of the electrons distribution in layers of the structure was carried out to understand the observed phenomena. The dependence of the tunneling transparency of the barrier separating the 2D and 3D transport channels in the structure, was studied as a function of the doping level, the degree of blurring boundaries, layer thickness, degree of relaxation of elastic stresses in the layers of the structure. Tunnel characteristics of the barrier between the layers were manifested by the appearance of a tunneling component in the current–voltage characteristics of real structures. Instabilities, manifested during the magnetotransport measurements using both weak and strong magnetic fields are explained by the transitions of charge carriers from the two-dimensional into three-dimensional state, due to interlayer tunneling transitions of electrons.     

超薄栅氧化层n-MOSFET软击穿后的导电机制

研究了恒压应力下超薄栅氧化层n型金属-氧化物-半导体场效应晶体管（n-MOSFET）软击穿 后的导电机制.发现在一定的栅电压V_g范围内，软击穿后的栅电流I_g符合Fowl er-Nordheim隧穿公式，但室温下隧穿势垒_b的平均值仅为0936eV，远小于S i/Si O₂界面的势垒高度315eV.研究表明，软击穿后，处于Si/SiO₂界 面量子化能级上的 电子不隧穿到氧化层的导带，而是隧穿到氧化层内的缺陷带上._b与缺陷带能 级和电 子所处的量子能级相关；高温下，激发态电子对隧穿电流贡献的增大导致_b逐 渐降低. 关键词： 软击穿 栅电流 类Fowler-Nordheim隧穿 超薄栅氧化层     

Co基磁性隧道结势垒结构的电子全息研究

利用高分辨电子显微术和电子全息方法研究了Co基磁性隧道结退火热处理前后的微观结构及相应势垒层结构的变化. 研究结果表明，退火处理可以明显地改善势垒层和顶电极、底电极之间的界面质量，改进势垒层本身的结构. 这与该磁性隧道结经过280℃退火处理后，隧道磁电阻值大大增加是一致的. 关键词： 磁性隧道结 隧道磁电阻 高分辨电子显微学 电子全息     

Investigation of HfO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>/<Emphasis Type="Italic">n</Emphasis>-Si(001)-based MOS structures via ballistic electron emission microscopy

(Au, Pt)/HfO₂/SiO₂/n-Si(001) metal-oxide-semiconductor structures with a thin (≈0.5 nm) SiO₂ layer, which is formed between HfO₂ and Si during atomic layer deposition of oxide layers, have been investigated via ballistic electron emission spectroscopy. The potential barrier heights at the (Au, Pt)/HfO₂ interfaces have been determined experimentally. The peculiarities observed in the curves of dependence of the collector current on the voltage between a scanning tunneling microscope probe and a metallic electrode are related to electron transport through the vacancy defect region of HfO₂ and the quantum-mechanical interference of electron waves arising from multiple reflections at the interfaces of the two-layer dielectric and at the interfaces of dielectric with a substrate and a metallic electrode.     

Annealing behavior of the Kondo-type zero-bias conductance peak in Ta-Ta2O5-Ag tunneling junctions

In annealing Ta-Ta₂O₅-Ag tunneling junctions the oxide barrier of which has been prepared by short-time room temperature oxidation, we observe a systematic decrease of the well-known Kondo-Appelbaum zero-bias anomaly. This decrease is due to electron transfer from low oxidation state magnetic Ta ions in the barrier near the Ta electrode to oxygen near the Ag electrode.     

Picosecond luminescence of AlxGa1-xAs and GaAs double quantum well structures under high pressure

Abstract

The time-resolved luminescence of an electron-hole plasma in Al_0.36Ga_0.64As was studied as a function of pressure. Application of hydrostatic pressure varies the energy separation between the conduction band minima at Г and X. The dependence of the intensity ratio of the zero-phonon line and the two phonon replicas on this energy separation shows that scattering from X to Г by alloy disorder is as effective as scattering by phonons. We have further studied the tunneling of electrons between two GaAs quantum wells (QW) of different thicknesses through an Al_0.35Ga_0.65As barrier. The lifetime of electrons in the narrow QW, which is limitd by electron tunneling into the wider QW, stays constant from 0 to 2.4 GPa, where it drops within 0.1 GPa from 140 ps to less than 7 ps. At this pressure the X-point energy of the barrier coincides with the electron level in the wider QW. We infer that tunneling occurs only via the Г states in the barrier and that X states become effective only when real-state transfer is possible.     

Potential barriers to electron tunnelling in ultra-thin films of SiO2

The oxide potential barrier in metal-SiO₂-Si junctions is examined experimentally for oxide thickness 4 ? 50 Å using tunnel currents. The importance is emphasized of finding the electron concentration, n_s, at the Si surface before deducing the tunneling transmission coefficient of the oxide barrier. n_s increases rapidly with increasing δ, and is larger with Al than with Au electrodes.The SiO₂ layers give appreciably lower transmission coefficients (1) with Al than with Au electrodes, and (2) for SiO₂ grown in wet O₂ at 900°C than for SiO₂ grown in dry O₂ at 700°C.     

电极处势垒对新结构器件电子输运的影响

在新结构薄膜电致发光器件中,电极处的势垒的高度决定电子的注入数量.在电极界面处插入不同的薄膜材料,可以改变势垒的高度,并对电子注入数量和器件的发光亮度产生影响.通过拟合计算得到ZnO/SiO,ITO/SiO的界面势垒高度分别为0.51和1.87eV. 关键词：     

The effect of non-constant effective tunneling mass and asymmetry for resonant tunneling in double-barrier structures

We discuss the transmission coefficient τ_d in non-repetitive, one-dimensional, rectangular double-barrier structures without simplifications such as strongly attenuating barriers, strong localization, or overall constant effective tunneling mass of the electron. For resonance τ_d=1, we obtain two non-approximative conditions which require different resonance energies of the tunneling electron than previously reported in the literature. In fact, the resonance peaks are shifted to higher energy levels in the order of the width of the peaks due to the effect of non-constant tunneling mass. We investigate the dependence of the resonance condition and the shape of the resonance peaks in regard to perturbation of the electron energy, the gap width as well as the barrier width and height. Resonance is stable for variation of the barrier width but sensitive for variation of the barrier height and the gap width. Received: 9 December 1998 / Accepted: 5 January 1999 / Published online: 31 March 1999     

d(x2-y2)+idxy混合波正常金属/绝缘层/超导体结中的隧道谱

考虑界面粗糙散射,在Blonder-Tinkham-Klapwijk(BTK)理论框架下,通过求解Bogoliubov-de-Gennes(BdG)方程,分别计算T=0K和有限温度下,d_(x²-y²)+id_xy混合波正常金属绝缘层超导体结中的准粒子输运系数和隧道谱.研究表明:隧道谱中的电导峰的劈裂程度强烈地依赖于d_xy波分量的强度、超导体的晶轴方位和界面粗糙强度,而温度的升高能压低电导峰. 关键词： NIS结 (x²-y²)+id_xy混合波超导体')" href="#">d_(x²-y²)+id_xy混合波超导体 隧道谱     

Oscillation modes,transient chaos and its control in a modulation-doped semiconductor double-heterostructure

The nonlinear dynamics of real space transfer for a 2D electron gas in a system of two adjacent Al _x Ga_1–x As/GaAs-heterolayers under parallel current conduction has been investigated numerically. The mechanisms which have been taken into account are transfer of electrons by thermionic emission and nonresonant tunneling and the delayed dielectric relaxation of the interface potential barrier. We predict bistability of an asymmetric and a symmetric self-generated oscillation mode, a quasiperiodic route to chaos and transient chaos with mean transient times obeying a universal critical scaling law. Unstable periodic orbits of the chaotic repeller can be stabilized by a simple delayed feedback control, thus providing a widely tunable semiconductor oscillator.     

Die Rotation des Elektronenspins beim ebenen Tunnelprozeß mit überlagertem homogenem Magnetfeld

Measurements of the spin polarization of field emitted electrons from various ferromagnetic (Gd, Ni, Fe) and nonferromagnetic metals (W) show a steady increase of the angle? _s between momentum and electron spin with increasing external magnetic field (spin rotation). This effect is refered to the coupling between the magnetic moment of the electron and the strong electric field in the potential barrier at the emitter surface during the tunneling process. A formal application of the equation of spin motion derived by Bargmann, Michel and Telegdi for an electron moving in homogeneous electromagnetic fields delivers a quantitative agreement with the experimental results.     

Fano resonances and electron localization in heterobarriers

A study is made of electron tunneling in semiconductor heterostructures having a complex dispersion law. A generalized Fabry-Perot approach is used to describe tunneling across the barrier. Mixing of electron states at the heterojunctions is responsible for the asymmetric resonant structure of the transmission which is characterized by a resonance-antiresonance pair. The resonance corresponds to a pole while the antiresonance corresponds to a zero of the scattering amplitude in the complex energy plane, i.e., near the pole and the zero the transmission of the heterobarrier has a Fano resonance structure. It is shown that for certain barrier parameters the resonances may collapse and localized states may appear in the heterobarrier, which is observed on the current-voltage characteristics of the barriers. The two-valley model of a GaAs/Al_xGa_1?x As/GaAs heterostructure is considered as an example. An analysis is made of the resonance structure in the barrier as a function of the type of boundary conditions used for the heterojunctions. The low-temperature current-voltage characteristic of the barrier is calculated.     

The a-Type K = 0 Microwave Spectrum of the Methanol Dimer

The rotational spectrum of (CH₃OH)₂ has been observed in the region 4-22 GHz with pulsed-beam Fabry-Perot cavity Fourier-transform microwave spectrometers at NIST and at the University of Kiel. Each a-type R(J), K_a = 0 transition is split into 15 states by tunneling motions for (CH₃OH)₂, (¹³CH₃OH)₂, (CH₃OD)₂, (CD₃OH)₂, and (CD₃OH)₂. The preliminary analysis of the methyl internal rotation presented here was guided by the previously developed multidimensional tunneling theory which predicts 16 tunneling components for each R(J) transition from 25 distinct tunneling motions. Several isotopically mixed dimers of methanol have also been measured, namely ¹³CH₃OH, CH₃OD, CD₃OH, and CD₃OD bound to ¹²CH₃OH. Since the hydrogen bond interchange motion (which converts a donor into an acceptor) would produce a new and less favorable conformation from an energy viewpoint, it does not occur and only 10 tunneling components are observed for these mixed dimers. The structure of the complex is similar to that of water dimer with a hydrogen bond distance of 2.035 Å and a tilt of the acceptor methanol of 84° from the O-H-O axis. The effective barrier to internal rotation for the donor methyl group of (CH₃OH)₂ is ν₃ = 183.0 cm⁻¹ and is one-half of the value for the methanol monomer (370 cm⁻¹), while the barrier to internal rotation of the acceptor methyl group is 120 cm⁻¹.     

Current-distance-voltage characteristics of electron tunneling through an electrochemical STM junction

We have studied the electron tunneling process through an electrochemical scanning tunneling microscopic (STM) junction formed by a gold tip and a gold electrode immersed in an inert NaClO₄ solution. Current-distance-voltage characteristics of the tunneling process are examined by simultaneous measurement of tunneling current, voltage, and distance. The results indicate that the tunneling voltage across the junction changes with tunneling distance; however, tunneling conductance is an inverse exponential function of distance over the entire investigated range of tunneling current, voltage, and distance. The results provide clear evidence for the validity of a one-dimensional tunneling model for the aqueous tunneling process. Implications of the observation are mentioned with regard to the distance-dependent STM imaging and the origin of a low tunneling barrier height.     

Resonant tunneling of electrons between two-dimensional systems of different densities in a quantizing magnetic field

The results of experimental investigation of the vertical electron transport in a GaAs/Al_0.3Ga_0.7As/GaAs single-barrier tunneling heterostructure with a doped barrier are presented. Two-dimensional accumulation layers appear on different sides of the barrier as a result of the ionization of Si donors in the barrier layer. The nonmonotonic shift of the current peak is found in the I–V curve of the tunneling diode in a magnetic field perpendicular to the planes of two-dimensional layers. Such a behavior is shown to be successfully explained in the model of appearing the Coulomb pseudogap and the pinning of the spin-split Landau levels at the Fermi levels of the contacts. In this explanation, it is necessary to assume that the Landé factor is independent of the filling factors of the Landau levels and is g* = 7.5 for both layers.     

Correlation between Si-SiO2 heterojunction and Fowler-Nordheim conduction mechanism after soft breakdown in ultrathin oxides

A stress-induced defect band model is proposed to investigate the Fowler-Nordheim tunneling characteristics of ultrathin gate oxides after soft breakdown. Soft breakdown occurs when the average distance between stress-induced defects locally reaches a critical value to overlap the bound electron wavefunction on adjacent defects and to form a defect band. This model shows that an n⁺-poly-Si/N-SiO₂/p-Si heterojunction structure is formed between electrodes at a local area after a soft breakdown in the ultrathin SiO₂ and the soft breakdown current can be described in terms of the Fowler-Nordheim tunneling process with a barrier height of ∼1 eV.