The use of antenna theory to calculate the electric fields in a thermal field emission metal whisker diode

In recent years, research groups have used metal-metal point contact diodes for frequency mixing and detection of infrared laser radiation. It has been postulated that the mechanism for the nonlinear current-voltage characteristic of the diode is the tunneling of electrons through an intermediate oxide film from the whisker tip to the metal base, i.e., the configuration is considered to be a metal-oxide-metal (MOM) tunneling junction. Several features of the diodes' operation create considerable doubt concerning the applicability of the MOM tunneling mechanism. Analysis of the available data led us to postulate an alternate solid state mechanism, namely a thermally enhanced field emission process. Such emission would be a consequence of the immersion of the whisker in the laser radiation resulting in (1) conduction heating which induces thermionic emission and (2) generation of an electric field at the tip necessary for electron tunneling. In an earlier paper, we calculated the power absorbed by the cylindrical shank of a point contact diode in an infrared radiation field. Using the absorbed power as a source, detailed calculations were made of the laser induced temperature distributions on the diode; more approximate treatments were used to obtain the electric fields developed on the tip. Values of the computed temperature and field parameters for tungsten were found to be consistent with a thermal field emission process. In this paper we present a more rigorous calculation of the voltages and fields induced on different metal whisker tips by the incident laser radiation. Linear antenna theory is used to describe the receiving properties of the diode. The actual pointed geometry of the diode tip has been taken into account using Schelkunoff's theory of the conical antenna. The electric fields at the tip are found to be comparable with those necessary for field emission. The highest fields are established on gold tips, consistent with the experiments of Green et al. who found the best responsivity occurs with gold-gold contacts. Finally we discuss the significance of the experimental results of Young et al. on metal-vacuum-metal tunneling characteristics to the MOM tunneling hypothesis.     

Thermal and field emission effects of laser radiation on metal whisker diodes: Application to infrared detection devices

In a series of recent experiments, research groups have made absolute frequency measurements with laser beams in the infrared region of the spectrum (λ ? 10 μm) using a metal point contact diode for generation, frequency mixing and detection. It has been postulated that the mechanism for the nonlinear current-voltage characteristic of the diode is tunnelling of electrons through an intermediate oxide film from the whisker into the metal base, i.e., the configuration is considered to be a metal-oxide-metal (MOM) tunnelling junction. Several features of the diode's operation create considerable doubt concerning the applicability of the MOM tunnelling mechanism. Analysis of the available experimental data led us to postulate an alternate solid state mechanism, namely a thermally enhanced field emission process. Such emission would be a consequence of the immersion of the whisker tip in the laser radiation resulting in (1) conduction heating which induces thermionic emission and (2) generation of an electric field at the tip necessary for electron tunnelling by field emission. In this paper we calculate rigorously the power absorbed in the metal whisker from the incident radiation. From the power absorbed, the heat conduction equation is solved for model geometries to obtain the laser induced temperature distribution at the whisker surface. Estimates of the electric field are obtained and combined with temperature calculations to obtain the nonlinear I–V characteristics of the thermally enhanced field emission model. Finally some simple experiments are proposed to test the thermal field emission hypothesis as a possible mechanism to explain the nonlinear characteristics of the metal whisker point contact diode.     

Thermal field emission as a mechanism for infrared laser light detection in metal whisker diode

The non-linear current-voltage characteristic of thermally enhanced field emission is proposed to explain the operation of a metal-metal point contact diode used for laser harmonic frequency generation and frequency mixing in the infrared region. This mechanism can explain several experimental observations which appear inconsistent with the previous analysis based on a planar metal-oxide-metal tunneling geometry.     

A Green's function solution to the image and multiple image interactions for hyperboloidal geometry: Application to metallic pointcontact infrared detectors

Using the Mehler-Fock transformation to solve Poisson's equation in prolate spheroidal coordinates, we have obtained an exact Green's function solution for all multiple image corrections to the vacuum tunneling barrier for a hyperboloidal tip-planar-anode model of a point-contact junction consisting of identical or dissimilar metals.These calculations show that the image corrections significantly modify both the form and area of the barrier, producing an enhancement in the rectification and tunneling currents at low bias.I–V characteristics have also been obtained for the hyperboloidal tip model using estimates of the emission and collection regions based on field emission experiments for whisker tips of comparable dimensions. These results are compared with earlier calculations whichThis research was supported in part by the NATO Research Grants Program, Grant No. 1902, Scientific Affairs Division, Brussels, BELGIUM.     

Electron tunnelling and polarity reversal of tungsten-nickel point-contact diodes

Tunnelling and rectification characteristics of MIM point contact diodes are interpreted in terms of the different electronic band structures of the two metals at the junction. The experimentally observed polarity reversal is shown to be consistent with the tunnelling mechanism describing the operation of the MIM diode.     

Thermally enhanced response of metal—oxide—metal diodes

It is shown that in thin-film MOM diodes of contact area ~ 2.5 × 10^-9 m² the basic mechanism of infrared and visible laser radiation detection is the tunneling current dependence on contact temperature (thermally enhanced tunneling). Experiments were run on Al—Al₂O₃—Al MOM diodes.     

Properties of monolithic integration of a resonant tunneling diode and a quantum well laser

An investigation of the electrical and optical characteristics of a resonant tunneling diode monolithically integrated with a quantum well laser is carried out. An analytic expression for the propagating model current is given in terms of the total spontaneous emission rate. The laser is pumped by the current emitted by the resonant tunneling diode. When the current in the laser exceeds the threshold current, laser light is produced. Since the current in the laser exhibits negative differential resistance similar in behavior to the current of a resonant tunneling diode, a bistable light output can be obtained from this new device.     

Response of metal-insulator-metal point contact diodes to visible laser light

Video response and mixing behaviour of metal-insulator-metal point contact diodes have been investigated for visible laser light. Thermally enhanced tunneling is shown to dominate the dc detection behavior of those diodes, while mixing of frequencies being more than several MHz apart is a more complex phenomenon involving thermal, field-and photo-assisted tunneling. In further experiments the potential of point contact diodes for optical heterodyne spectroscopy was examined. Two green laser lines of 122 GHz frequency difference were mixed with the second harmonic of an appropriate microwave frequency, generated simultaneously on the diode. The modestS/N ratio achieved has to be assigned to the different behaviour of metal-insulator-metal diodes in the visible and rf range.     

Dependence of negative resistance characteristics of avalanching MIM diodes on current injection mechanisms

Current-controlled negative resistance characteristics are computed for avalanche injection metal/insulator/metal diodes. Current injection is taken to occur by either Schottky thermionic emission or the Fowler-Nordheim tunneling mechanism. The results presented show that the diode negative resistance characteristics depend critically on both the magnitude and field dependance of injected currents.     

Significant Fowler–Nordheim tunneling across ZnO – Nanorod based nanojunctions for nanoelectronic device applications

We demonstrate significant Fowler–Nordheim (FN) tunneling across Al/Al₂O₃/ZnO metal–insulator–semiconductor (MIS) and Ag/ZnO metal–semiconductor (MS) nanojunctions. The transport properties of ZnO nanostructures in the form of urchins and randomly distributed nanorods were investigated in terms of various conduction mechanism. The minimum voltage necessary for triggering Fowler–Nordheim (FN) tunneling, under forward biasing, was ～1.2 V and ～3.4 V; respectively, below which only direct tunneling and thermionic emission events were evident. Mediated through Al₂O₃ layer, the FN tunneling was more prominent across MIS junction than MS one. The weak FN tunneling across MS junction was owing to interfacial charge transfer process through the atomic scale gapping between adjacent nanostructures. The extent of such type of tunneling is found to be nanostructure morphology dependent and largely rely on the free electrons donated by the native donor defects in the crystal structure of ZnO. The significant FN tunneling across the MIS and MS junctions has a direct relevance in designing nanoscale field emission devices/components working at low voltage with high throughputs.     

Dynamic thermal modeling and parameter identification for monolithic laser diode module

We improve the thermal equivalent-circuit model of the laser diode module (LDM) to evaluate its thermal dynamic property and calculate the junction temperature of the laser diode with a high accuracy. The thermal parameters and the transient junction temperature of LDM are modeled and obtained according to the temperature of the thermistor integrated in the module. Our improved thermal model is verified indirectly by monitoring the emission wavelength of the laser diode against gas absorption lines, and several thermal parameters are obtained with the temperature uncertainty of 0.01 K in the thermal dynamic process.     

Dynamic thermal modeling and parameter identification for a monolithic laser diode module

We improved the thermal equivalent-circuit model of the laser diode module(LDM) to evaluate its thermal dynamic properties and calculate the junction temperature of the laser diode with a high accuracy.The thermal parameters and the transient junction temperature of the LDM are modeled and obtained according to the temperature of the thermistor integrated in the module.Our improved thermal model is verified indirectly by monitoring the emission wavelength of the laser diode against gas absorption lines,and several thermal parameters are obtained with the temperature uncertainty of 0.01 K in the thermal dynamic process.     

Rectification mechanism in diblock oligomer molecular diodes

We investigated a mechanism of rectification in diblock oligomer diode molecules that have recently been synthesized and showed a pronounced asymmetry in the measured I-V spectrum. The observed rectification effect is due to the resonant nature of electron transfer in the system and the localization properties of bound state wave functions of resonant states of the tunneling electron interacting with an asymmetric molecule in an electric field. The asymmetry of the tunneling wave function is enhanced or weakened depending on the polarity of the applied bias. The conceptually new theoretical approach, the Green's function theory of sub-barrier scattering, is able to provide a physically transparent explanation of this rectification effect based on the concept of the bound state spectrum of a tunneling electron. The theory predicts the characteristic features of the I-V spectrum in qualitative agreement with experiment.     

Spontaneous emission of atoms in a strong laser field

The spontaneous emission of an atomic system in the field of a high-intensity femtosecond laser pulse is considered within the framework of a consistent quantum-mechanical approach based on an examination of the interaction of a quantum system with a set of quantized field modes in a vacuum state. Both even and odd harmonics of the driving field are shown to appear in the atomic emission spectrum, and the mechanisms of their generation are elucidated. A comparison with the semiclassical theory of laser harmonic generation is made. The semiclassical approach in describing the spontaneous emission in strong laser fields, especially under conditions of significant depletion of the ground (initial) state in a laser field, is shown to be limited.     

Spin-Torque Diodes: From Fundamental Research to Applications

Among a rich variety of emerging spintronic devices, spin-torque diodes (STDs) are among the most interesting, from both a fundamental and an applied perspective. The spin-torque diode effect occurs when a microwave alternating electric current injected into a magnetic tunneling junction (MTJ) is rectified due to the simultaneous actions of tunneling magnetoresistance and spin-transfer torque. While the sensitivity of STDs observed in the initial research is rather modest (about 1.4 mV mW⁻¹), after only a few years researchers have increased it to 200 kV W⁻¹ and demonstrated rectification at nanowatt input powers, which radically exceeds the capabilities of mainstream Schottky diodes. This impressive progress is based on a deep understanding of the complex STD physics and on recent advances in MTJ fabrication technology. Herein, the experimental pathways toward increasing the sensitivity and extending the frequency range of STDs and theoretical works aimed at explaining the complex nonlinear dynamics are analysed, and a wide variety of possible STD applications are discussed.     

The I-V characteristics of double barrier stair-wells

We investigated the I-V characteristics of the double barrier stair-well structure. Resonant tunneling current is achieved by application of an electric field, which increases the transmission under positive bias and decreases it under the reverse bias. This asymmetry can be used for rectification and the device works as a quantum diode. Furthermore, the same structure can perform, under negative bias, resonant tunneling processes with different characteristics.     

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.     

Influence of dissipation on phase tunneling in Josephson-junctions

The coupling between the phase and the electromagnetic field in the case of a tunnel junction is treated by Feynmans path integral method. It is shown that the elimination of the field leads to a frequency dependent mass for the motion of the phase , which is simply related to the effective dielectric constant of the junction. Considering tunneling as a motion in imaginary time one obtains a polaron like mass enhancement connected to the dielectric function at positive imaginary frequencies, which essentially leads to the Caldeira-Leggett reduction of the elastic tunneling probability. In the weak damping limit it is shown that the emission of real excitations during tunneling is a higher order effect. At low temperatures the damping finally is determined by the linewidth of electromagnetic radiation at the Josephson plasma frequency.     

Generation of electromagnetic waves in the terahertz frequency range by optical rectification of a Gaussian laser pulse in a plasma in presence of an externally applied static electric field

We propose a theoretical model for the generation of electromagnetic waves in the terahertz (THz) frequency range by the optical rectification of a Gaussian laser pulse in a plasma with an applied static electric field transverse to the direction of propagation. A Gaussian laser pulse can exert a transverse component of the quasi‐static ponderomotive force on the electrons at a frequency in the THz range by a suitable choice of the laser pulse width. This nonlinear force is responsible for the density oscillation. The coupling of this oscillation with the drift velocity acquired by electrons due to the applied static electric field leads to the generation of a nonlinear current density. A spatial Gaussian intensity profile of the laser beam enhances the generated THz yield by many folds as compared to a uniform spatial intensity profile.     

Pt/Au/n-InGaN肖特基接触的电流输运机理

基于热电子发射和热电子场发射模式,利用I-V方法研究了Pt/Au/n-InGaN肖特基接触的势垒特性和电流输运机理,结果表明,在不同背景载流子浓度下,Pt/Au/n-InGaN肖特基势垒特性差异明显.研究发现,较低生长温度制备的InGaN中存在的高密度施主态氮空位（V_N）缺陷导致背景载流子浓度增高,同时通过热电子发射模式拟合得到高背景载流子浓度的InGaN肖特基势垒高度和理想因子与热电子场发射模式下的结果差别很大,表明V_N缺陷诱发了隧穿机理并降低了肖特基势垒高度,相应的隧穿电流显著增大了肖特基势垒总的输运电流,证实热电子发射和缺陷辅助的隧穿机理共同构成了肖特基势垒的电流输运机理.低背景载流子浓度的InGaN肖特基势垒在热电子发射和热电子场发射模式下拟合的结果接近一致,表明热电子发射是其主导的电流输运机理.