Doping induced diode behavior with large rectifying ratio in graphyne nanoribbons device

By applying nonequilibrium Green's functions (NEGF) in combination with density functional theory (DFT), the electronic transport properties of α-armchair graphyne nanoribbons (α-AGyNR) device are investigated, in which the left electrode is doped by Boron (B) atoms and the right electrode is doped by Nitrogen (N) atoms. B and N doping atoms that are substituted in SP and SP² sites result in four devices named as A (sp–sp), B (sp²–sp²), C (sp²–sp) and D (sp–sp²). The current–voltage characteristics of these systems reveal that the proposed devices have a striking nonlinear feature that leads to formation of a p–n junction which results rectifying behavior. The results show that the rectification characteristics are strongly dependent on the site of doping atoms. In A and D devices the rectification ratio (RR) can reach to 10³ in the bias region from 0.2 V to 0.6 V while in B and C devices the RR can be enlarged to 10⁴ in the same bias region. Unlike the most of the previous proposed molecular rectifiers that are vertical hetero structures, the proposed rectifier in this work is in-plane or two dimensional structures. The results provide a new insight and a novel effective pathway for developing applicable high-performance Graphyne-based rectifiers.     

The ampere-second characteristic of high-power silicon rectifiers

An examination of the conditions under which high-power silicon rectifiers lose thermal stability is presented. A method is given for calculating the ampere-second characteristics, and graphs of limiting p-n junction temperature during overload are presented, as well as the ampere-second characteristic of a VK-200 for certain load conditions. Reference is made to methods of extending the limits of thermal stability of this device, as well as the rectified current density.It is possible to use the ampere-second characteristic of a semiconductor device as a measure of its overload capacity, that is, the dependence of the direct current overload on the time during which the device can sustain this current without damage to the rectifying element. Current overload protection in rectifier units should be selected in this way so that the ampere-second characteristic lies below that of the device being protected.Hence the calculation of the ampere-second characteristic of silicon power devices assumes considerable importance in the design of new rectifier units from the point of view of reliability and continuous operation at maximum efficiency.     

The world of many worlds

The efficient conversion of electrical power from AC to DC is one of the most important problems in electrical technology. The ideal rectifier will present a short circuit path to current flowing in one direction, and an open circuit in the opposite direction. All practical rectifiers have a finite resistance in the conducting or forward direction and measurable leakage in the blocking or reverse direction; further, they all cease to block at all beyond a certain voltage. There is always a certain temperature for each type of rectifier above which its efficiency drops rapidly. The most important features of any rectifier are therefore:     

Junction barrier Schottky rectifier with an improved P-well region

<正>A junction barrier Schottky（JBS） rectifier with an improved P-well on 4H-SiC is proposed to improve the V_F-I_R trade-off and the breakdown voltage.The reverse current density of the proposed JBS rectifier at 300 K and 800 V is about 3.3×10^-8 times that of the common JBS rectifier at no expense of the forward voltage drop.This is because the depletion layer thickness in the P-well region at the same reverse voltage is larger than in the P⁺ grid,resulting in a lower spreading current and tunneling current.As a result,the breakdown voltage of the proposed JBS rectifier is over 1.6 kV,that is about 0.8 times more than that of the common JBS rectifier due to the uniform electric field.Although the series resistance of the proposed JBS rectifier is a little larger than that of the common JBS rectifier,the figure of merit（FOM） of the proposed JBS rectifier is about 2.9 times that of the common JBS rectifier.Based on simulating the values of susceptibility of the two JBS rectifiers to electrostatic discharge（ESD） in the human body model（HBM） circuits,the failure energy of the proposed JBS rectifier increases 17%compared with that of the common JBS rectifier.     

超宽带声螺旋结构

超材料慢声器件具有非常灵活的相位控制能力,能够实现超薄的声透镜、声学整流器和声学自加速发生器等多种声学功能器件。但是,大多数慢声器件存在严重的色散、界面阻抗不匹配等问题,限制慢声器件只能在较窄的带宽工作。文章介绍了一种全新的螺旋型慢声器件,回顾了均匀螺距的螺旋结构超材料和螺距连续变化的螺旋结构超材料,深入分析了实现宽带零色散慢声器件和宽带高耦合效率的慢声器件的基本原理和设计规则。这些慢声器件可通过调整结构的螺距来灵活实现相位调节。最后,文章从数值和实验两个方面证明了按照一定规律排列的螺旋结构型超材料单元可以将入射的平面声波转换成按预设抛物线轨迹传输的艾里声束。     

电荷耦合效应对高耐压沟槽栅极超势垒整流器击穿电压的影响

通过沟槽结构和可调节的电子势垒,沟槽栅极超势垒整流器可以更为有效地实现通态压降和反向漏电流之间的良好折衷.在高压应用时,电荷耦合效应对于提高该器件的反向承压能力起到了关键作用.本文通过理论模型与器件模拟结果,分析了沟槽深度、栅氧厚度和台面宽度等关键参数对电荷耦合作用下二维电场分布的影响,归纳出了提高该器件击穿电压的思路与方法,为器件设计提供了有意义的指导.在此基础上,提出了阶梯栅氧结构,该结构在维持几乎相同击穿电压的同时,使正向导通压降降低51.49%.     

分子器件的研究进展

分子器件作为下一代电子器件近年来得到了迅速的发展.文章回顾了分子器件的发展历程和研究现状,并重点对分子导线、分子开关、分子整流器和分子晶体管等器件进行了介绍.     

Thermal transport in four-terminal graphene nano-junctions

The thermal transport properties of four-terminal graphene nano-junctions (FGNJs) consisting of semi-infinite armchair-edged nanoribbon and zigzag-edged nanoribbon were calculated. The thermal transport in FGNJs is sensitive to their geometric shape. The thermal conductance of FGNJs depends on the width of semi-infinite graphene nanoribbons and center region. These thermal transport phenomena can be explained by analyzing the phonon transmission coefficient. Compared with previous thermal rectifiers, reverse modulation can be obtained by changing the width of the thermal terminal. The results provide significant physical models and theoretical validity in designing the thermal devices based on the graphene nano-junctions.     

Prebreakdown condition in selenium rectifiers

This paper reports data from an experimental investigation of the prebreakdown and breakdown conditions of factory production selenium rectifiers in the temperature range from 100 ° to –196 ° C when a unit voltage pulse with steep leading edge (rise time about 10^–8 sec) is applied to the rectifier in the non-conducting direction. Change in voltage across the rectifier and in current through it were recorded by a two-channel high-speed electronic oscilloscope. On the basis of this test data, the variation of discharge rise-time in the selenium p-n junction as a function of overvoltage and temperature was determined, the formation of current pulses was detected in the junction, both before and during breakdown in the temperature range from 100 ° to –196 ° C, and it was also established that breakdowns of selenium rectifier p-n junctions are due to joint action of the Zener effect and impact ionization.We are indebted to Prof. Kh. I. Amirkhanov for his constant interest in this work.     

Self-assembled and electrochemically deposited mono/multilayers for molecular electronics applications

For the development of molecular electronics, it is desirable to investigate characteristics of organic molecules with electronic device functionalities. In near future, such molecular devices could be integrated with silicon to prepare hybrid nanoelectronic devices. In this paper, we review work done in our laboratory on study of characteristics of some functional molecules. For these studies molecular mono and multilayers have been deposited on silicon surface by self-assembly and electrochemical deposition techniques. Both commercially available and specially designed and synthesized molecules have been utilized for these investigations. We demonstrate dielectric layers, memory, switching, rectifier and negative differential resistance devices based on molecular mono and multilayers.     

D-B-A分子整流特性的端基效应

利用密度泛函理论和非平衡格林函数方法,研究了基于同一D-B-A分子在改变端基后形成的4个不同的分子器件的电子输运特性及整流效果.研究表明:端基的改变,能明显影响分子器件的整流效果,这是因为端基能影响分子与电极的耦合程度,从而改变了分子轨道的离域性,进而影响分子的电子输运特性及整流效果.更有趣的是,由于分子轨道HOMO和LUMO随偏压极性不同的非对称移动,导致整流器的整流方向与Aviram和Ratner分子整流器相反. 关键词： 分子整流器 端基 密度泛函理论 非平衡格林函数     

Possibility designing half-wave and full-wave molecular rectifiers by using single benzene molecule

This work focused on possibility designing half-wave and full-wave molecular rectifiers by using single and two benzene rings, respectively. The benzene rings were threaded by a magnetic flux that changes over time. The quantum interference effect was considered as the basic idea in the rectification action, the para and meta configurations were investigated. All the calculations are performed by using steady-state theoretical model, which is based on the time-dependent Hamiltonian model. The electrical conductance and the electric current are considered as DC output signals of half-wave and full-wave molecular rectifiers. The finding in this work opens up the exciting potential to use these molecular rectifiers in molecular electronics.     

Controlling the heat flow: now it is possible

We discuss the problem of heat conduction in 1D nonlinear chains in relation to the dynamical properties of the system. We provide convincing numerical evidence for the validity of Fourier law of heat conduction in linear mixing systems. Therefore, deterministic diffusion and normal heat transport which are usually associated with full hyperbolicity, actually take place in systems without exponential instability. We then show that, acting on the parameter which controls the strength of the on site potential inside a segment of the chain, we induce a transition from conducting to insulating behavior in the whole system. The control of heat conduction by nonlinearity opens the possibility to propose new devices such as a thermal rectifier.     

分子整流器的相关技术

分子整流器的相关技术是研究器件基础理论和未来付诸应用的关键问题之一。由于分子材料的特殊物理化学性质,原本成熟的普通半导体工艺不再适用。本文综述了目前在分子整流器研究领域广泛使用的相关技术,介绍了分子有序排列的各种组装技术,ＳＴＭ技术,电极制备技术等。分子器件的深入研究将会引起信息处理系统和材料科学的发展,对未来科学技术和社会发展产生深远的影响。     

Effect of proportion on rectification in organic co-oligomer spin rectifiers

The rectification behaviours in organic magnetic/nonmagnetic co-oligomer spin rectifiers are investigated theoretically.It is found that both the charge current and the spin current through the device are rectified at the same time.By adjusting the proportion between the magnetic and nonmagnetic components,the threshold voltage and the rectification ratio of the rectifier are modulated.A large rectification ratio is obtained when the two components are equal in length.The intrinsic mechanism is analysed in terms of the asymmetric localization of molecular orbitals under biases.The effect of molecular length on the rectification is also discussed.These results will be helpful in the future design of organic spin diodes.     

A single-electron circuit as a discrete dynamical system

A single-electron circuit can be operated as a discrete dynamical system because it changes its internal state discontinuously because of electron tunneling. To confirm this idea, we designed a sample circuit for discrete dynamical operation and confirmed by computer simulation that the circuit successfully generated a sequence of discrete-time outputs by following a return map. The concept of discrete dynamical systems will be useful in developing new functional systems that consist of quantum devices and nanostructures.     

Nonlinear electron transport properties of InAlAs/InGaAs based Y-branch junctions for microwave rectification at room temperature

A detailed analysis of nonlinear effects-electron switching and rectification, in InAlAs/InGaAs based Y-branch junction (YBJ) devices is presented to investigate the potential of YBJ for high frequency applications at 300 K. Results based on semi-classical simulations yield good qualitative agreement with measurements and previously reported theoretical and experimental results. The nonlinear parabolic behaviour of our device is attributed to device geometry and space charge effects. RF analysis shows that the YBJ has tremendous intrinsic potential to function as a frequency doubler and microwave rectifier when operated in the parabolic regime. The present analysis serves as a tool to optimize the bias conditions for RF measurements and to estimate the effect of interconnects and parasitic elements on the RF performance of real devices.     

Dielectrophoretically aligned GaN nanowire rectifiers

We demonstrate GaN nanowire (NW) current rectifiers which were formed by assembling n-GaN nanowires on a patterned p-Si substrate by means of alternating current (ac) dielectrophoresis. The dielectrophoresis was accomplished at a frequency of 10 kHz with three different ac bias voltages (5, 10, and 15 V_p–p), indicating that the number of aligned GaN nanowires increased with increasing ac bias voltage. The n-GaN NW/p-Si diodes showed well-defined current rectifying behavior with a forward voltage drop of 1.2–1.5 V at a current density of 200 A/cm². We observed that the GaN NW diode functioned well as a half-wave rectifier. PACS 71.20.Nr; 73.40.Cg; 73.40.Ei; 73.40.Kp     

High-Power GaN Electronic Devices

Gallium Nitride (GaN) and related materials (especially AlGaN) recently have attracted a lot of interest for applications in high-power electronics capable of operation at elevated temperatures and high frequencies. The AlGaInN system offers numerous advantages. These include wide bandgaps, good transport properties, the availability of heterostructures (particularly AlGaN/GaN), the experience base gained by the commercialization of GaN-based laser and light-emitting diodes and the existence of a high growth rate epitaxial method (hydride vapor phase epitaxy, HVPE) for producing very thick layers or even quasisubstrates. These attributes have led to rapid progress in the realization of a broad range of GaN electronic devices. Al_xGa_1-xN (x=0 ～.25) Schottky rectifiers were fabricated in a lateral geometry employing p⁺-implanted guard rings and rectifying contact overlap onto an SiO₂ passivation layer. The reverse breakdown voltage (V_B) increased with the spacing between Schottky and ohmic metal contacts, reaching 9700 V for Al_0.25Ga_0.75N and 6350 V for GaN, respectively, for 100-µm gap spacing. Assuming lateral depletion, these values correspond to breakdown field strengths of <9.67×10⁵ Vcm^?2, which is roughly a factor of 5 lower than the theoretical maximum in bulk GaN. The figure of merit (V_B)²/R_ON, where RON is the on-state resistance, was in the range 94 to 268 MWcm^?2 for all the devices. Edge-terminated Schottky rectifiers were also fabricated on quasibulk GaN substrates grown by HVPE. For small-diameter (75?µm) Schottky contacts, Vs measured in the vertical geometry was ～700?V, with an on-state resistance (RON) of 3?mΩcm², producing a figure-of-merit V_B ²/R_ON of 162.8?MW-cm^?2. GaN p-i-n diodes were also fabricated. A direct comparison of GaN p-i-n and Schottky rectifiers fabricated on the same GaN wafer showed higher reverse breakdown voltage for the former (490?V vs. 347?V for the Schottky diodes), but lower forward turn-on voltages for the latter (～3.5?V vs. ～5?V for the p-i-n diodes). The forward I-V characteristics of the p-i-n rectifiers show behavior consistent with a multiple recombination center model. The reverse current in both types of rectifiers was dominated by surface perimeter leakage at moderate bias. Finally, all of the devices we fabricated showed negative temperature coefficients for reverse breakdown voltage, which is a clear disadvantage for elevated temperature operation. Bipolar devices are particularly interesting for high current applications such as microwave power amplifiers for radar, satellite, and communication in the l～5?GHz range, powers >l00?W, and operating temperatures >425°C. pnp Bipolar Junction Transistors and pnp Heterojunction Bipolar Transistors were demonstrated for the first time. For power microwave applications, small area self-aligned npn GaN/AlGaN HBTs were attempted. The devices showed very promising direct current characteristics.     

Laserlike vibrational instability in rectifying molecular conductors

We study the damping of molecular vibrations due to electron-hole pair excitations in donor-acceptor (D-A) type molecular rectifiers. At finite voltage additional nonequilibrium electron-hole pair excitations involving both electrodes become possible, and contribute to the stimulated emission and absorption of phonons. We point out a generic mechanism for D-A molecules, where the stimulated emission can dominate beyond a certain voltage due to the inverted position of the D and A quantum resonances. This leads to current-driven amplification (negative damping) of the phonons similar to laser action. We investigate the effect in realistic molecular rectifier structures using first-principles calculations.