Effect of radial growth rate variation on resonant tunneling diode current-Voltage characteristics

The uniformity of electronic device characteristics is dependent on the uniformity of the epitaxial material. Uniformity is particularly important for resonant tunneling diodes where small changes in well or barrier thickness can have profound effects on the diode current-voltage characteristics. The variability of these characteristics due to growth rate nonuniformity for epitaxial structures grown by molecular beam epitaxy has been documented and the magnitude of the thickness variations analyzed using photoluminescence and a theoretical model. An increase of 17 meV was observed in the quantum well ground state, corresponding to a 15% thinning of the well from the center to the edge of the substrate.     

Inverted bistability in the current-voltage characteristics of a resonant tunneling device

The current-voltage characteristics of an asymmetric double barrier resonant tunneling device show a butterfly-shaped hysteresis loop in which, for a range of voltage, the off-resonant current exceeds the resonant current. This “inverted bistability” is due to the effects of space charge buildup in the quantum well. Magnetoquantum oscillations in the tunnel current with | are used to investigate the distribution of charge within the device and the intersubband scattering processes which control the charge buildup.     

Investigation on resonant tunneling in GaAs/AlxGa1-xAs DBD using tunneling spectroscopy

 Experimental investigation on resonant tunneling in various GaAs/Al_xGa_(1-x)As double barrier single well structures has been performed by using tunneling spectroscopy at different temperatures.The results show that in addition to resonant tunneling via GaAs well state confined by Al_xGa_(1-x)As Γ-point barrier there exists resonant tunneling via GaAs well state confined by Al_xGa_(1-x)As X-point barrier for both indirect(x>0.4)and direct(x<0.4)cases.     

A study of resonant tunneling in a 3-terminal ballistic device

Preliminary results are presented for a 3-terminal device fabricated by incorporating a narrow quantum well into the collector barrier of a unipolar hot electron transistor. The structure allows unique studies of the mechanism of resonant tunneling in which the carrier injection energy and the bias across the double barrier can be independently varied. The transistor clearly shows an additional current collection threshold representing as much as 10% of the injected current attributable to tunneling via the single subband in the quantum well. This interpretation is confirmed by measurements in perpendicular and parallel magnetic fields despite the fact that theoretical estimates of the resonant tunneling current without scattering are many orders of magnitude smaller, and there are strong indications that elastic scattering in the well is responsible for the enormous discrepancy. The data tend to support proposals (Guéret, 1989a, 1989b; Wolak, 1988) that elastic scattering is responsible for the large valley currents in resonant tunneling diodes, and it appears that the tunnel process may not be completely incoherent as has frequently been assumed up to now.     

Space-charge effects and ac response of resonant tunneling double-barrier diodes

We analyse theoretically the small-signal ac response of a resonant tunneling double-barrier semiconductor diode using the sequential tunneling approach. Electrostatic feedback effects due to space charge buildup in the quantum well are included in the analysis. The results are expressed in terms of an equivalent circuit which is used to interpret measurements of the capacitance of an asymmetric double-barrier structure at low frequencies (< 1 MHz). The frequency dependence of the real and imaginary parts of the impedance at microwave frequencies are also discussed.     

Imperfections and resonant tunneling in quantum-well heterostructures

We discuss effects of structural imperfections on the I-V characteristics and local density-of-states of semiconductor double-barrier heterostructures. Using a linear-chain model for GaAs/AlGaAs structures, we simulate fluctuations in layer thicknesses, defects at the heterointerfaces, and disorder.     

Influence of MBE growth temperature on GaAs/AlAs resonant tunneling structures

Double barrier GaAs/AlAs tunneling structures with typical 2.5:1 room temperature peak-to-valley current ratios are examined using Deep Level Transient Spectroscopy. Deep level trap concentrations are found to be much higher in samples grown at 550° C compared to those grown at 650° C. For devices grown at 550° C, an impedance switch-ing effect due to a high concentration of deep levels is observed. The peak-to-valley ratio of the tunneling devices is largely unaffected by the growth temperatures in this range, indicating that higher growth temperatures can be employed to grow resonant tunnel-ing diodes than previously suggested in the literature.     

Design, fabrication and operation of a hot electron resonant tunneling transistor

Transistors employing resonant tunneling injection of hot electrons into a thin quantum well base region have been fabricated. The base region in these transistors is formed by a narrow bandgap material like InGaAs so that the first level is a confined one lying below the Fermi level in the contact regions. This results in charge transfer into the bound state in the quantum well thus allowing independent control of the base electrostatic potential. Theoretical calculations showing the importance of various device parameters in the design of a resonant tunneling transistor are presented and preliminary results showing the capability of transistor action in such devices are presented.     

Role of structure sizes in determining the characteristics of the resonant tunneling diode

Using the Wigner function formalism, we study the effects of structural parameters on the DC I-V characteristics and on the large-signal transient response of the resonant tunneling diode. We model two types of structures of GaAs/Al_xGa_1-xAs; first, with symmetric barriers ranging from 3 to 8 nanometers in thickness separated by a 5 nanometer well, and second with a well varying from 3 to 8 nanometers between 3 nanometer barriers. Experimental variation of the barrier thickness and height changes the peak-to-valley ratio in the I-V curve, as predicted by elementary models of tunneling structures. This stems directly from the changes in tunneling probabilities. For the DC studies, we show that the peak-to-valley ratio in the I-V curve is a function of the resonance width, which depends both on the well and barrier thickness. The location of the peak on the I-V curve depends on the location of the resonant energy, which is a function of the well width. Transient switching behavior is compared to earlier numerical studies of tunneling times of wave packets. Charge storage stabilizes the position of the resonant state, thus damping the transients. Consequently, wider barriers yield faster transient settling times, in agreement with the tunneling time results which predicted longer charge storage times for thicker barriers.     

Analysis of defect-assisted tunneling based on low frequency noise measurements of resonant tunnel diodes

An experimental apparatus and procedure using noise measurement techniques have been developed in order to identify conduction mechanisms in RTDs due to defect assisted tunneling. The theory of noise measurements is discussed as the basis for the appropriate modelling of RTD noise data. The activation energies and capture cross-sections have been determined in a typical RTD for each of three distinct trap levels. A conjecture is made as to the physical location of the traps. This interpretation yields qualitative behavior consistent with the known bias and temperature dependence of the experimental results.     

倍增型共振隧穿弱光探测器的噪声性能研究

对倍增型共振隧穿弱光探测器(RTDPD,resonant tunneling diode as photodetector)的噪声性能 进行研究。设计了具有倍增区的RTDPD结构。对探测器电流-电压(I-V) 特性的模拟发现,加入倍增区 以后探测器的光电流和暗电流均被放大,其峰值电流增大了1.7倍。 对RTDPD的噪声分布模拟发 现,1/f噪声比散粒噪声和热噪声高出10 个数量级左右。对倍增 区的电场强度和过剩噪声因子进行了模拟, 并计算了过剩噪声的功率谱密度。分析了倍增型RTDPD的总噪声,并对有、无倍增区时RTDPD 的噪声等 效功率进行了计算。结果显示,倍增区引入的噪声不仅不会影响探测器有效信号的提取,而 且提高了探测器响应弱光的能力。     

谐振式隧穿磁强计的理论研究

分析了隧道扫描显微镜和隧穿磁强计的区别 ,认为隧穿磁强计的隧尖不需要也不应该过尖。研究了隧道间隙和隧道电流的关系。研究表明 ,虽然按照隧道效应理论 ,隧道间隙和隧道电流应该成指数关系 ,但对隧穿磁强计而言 ,其隧道电流和隧道间隙的关系可以近似看作线性关系。推导了谐振式隧穿磁强计的灵敏度计算公式     

基于Pspice的RTD等效模型及其应用电路研究

简要介绍了RTD(共振隧穿二极管)的微分负阻特性及其等效电路,通过对实际AlAs/InxGa1-xAs/GaAs双势垒共振隧穿结构I-V曲线拟合,得出RTD的Pspice等效电路模型参数。采用Pspice软件建立了RTD的等效电路模型,并对其微分负阻特性进行了仿真,仿真结果与测试结果基本吻合。利用所建立的模型,对RTD的基本应用电路:反相器、非门、与非门和或非门进行了仿真模拟。结果表明,该类电路能够正确实现其逻辑功能。最后,对基于RTD的振荡电路进行了仿真,仿真频率与实际测试频率处于同一数量级。由于实测电路寄生参数如串联电阻、电容等的影响,仿真结果与测试结果稍有出入。     

硅基隧穿二极管

隧穿二极管是一种很有前途的基于带隙工程的异质结构量子器件,其电流电压(I-V)曲线中所呈现的微分负阻特性能够用于开发多种不同的电路功能。在最近的研究中,空穴型双势垒单势阱共振隧穿二极管得到了实现,为Si1-xGex/Si异质结隧穿二极管器件的改进和电路应用打下了良好的基础。     

A vertical resonant tunneling transistor for application in digitallogic circuits

A vertical resonant tunneling transistor (VRTT) has been developed, its properties and its application in digital logic circuits based on the monostable-bistable transition logic element (MOBILE) principle are described. The device consists of a small mesa resonant tunneling diode (RTD) in the GaAs/AlAs material system surrounded by a Schottky gate. We obtain low peak voltages using InGaAs in the quantum well and the devices show an excellent peak current control by means of an applied gate voltage. A self latching inverter circuit has been fabricated using two VRTTs and the switching functionality was demonstrated at low frequencies     

共振隧穿二极管

设计并研制出室温工作的共振隧穿二极管,室温电流峰谷比达到7.6:1,最高振荡频率为54GHz。本文对RTD的设计、研制过程、参数和特性测试进行了系统的分析和说明。     

器件模拟对AlGaAs/GaAs RTD的特性分析(英文)

使用SILVACO公司的器件模拟软件ATLAS对AlGaAs/GaAs共振隧穿二极管(RTD)进行了器件模拟,得到了不同结构的RTD的I-V特性曲线。对量子阱宽度、掺杂浓度、势垒宽度和高度对RTD的I-V特性的影响进行了详细的分析。     

共振隧穿二极管的设计和研制

用分子束外延在半绝缘砷化镓上生长两垒一阱结构,制成RTD单管。经过材料生长设计、工艺设计和版图设计几方面的改进,测得最高振荡频率已达54GHz。     

Design of ternary flip-flops and sequential circuits based uponU hgate

According to the next-state equations of various ternary flip-flops (tri-flop), which are based upon ternary modular algebra, various ternary flip-flops are implemented by using universal-logic-modules,U _hs. Based on it ternary sequential circuits are implemented by using array of universal-logic-modules,U _hs. Supported by the National Natural Science Foundation of Zhejiang Province, China.     

Opportunities in dilute nitride III-V semiconductors quantum confined p-i-n solar cells for single carrier resonant tunneling

Stunning theoretical efficiencies have been predicted for quantum-confined solar cells. However, practical realizations remain inefficient as these devices suffer from an inherent difficulty in the extraction of photo-generated carriers from the confined states. Leveraging on the shallow valence band offset of dilute nitrides and using a carefully chosen material system and device design, we show the possibility of circumventing this problem by separating the optimization of the valence and conduction band and reducing the issue to a single particle problem. Band structure calculations including strain effects, band anti-crossing models and transfer matrix methods are used to theoretically demonstrate optimum conditions for enhanced vertical transport. High-electron tunneling escape probability, together with a free movement of quasi-3D holes, is predicted to result in enhanced PV device performance. Furthermore, the increase in electron effective mass due to the incorporation of N translates in enhanced absorptive properties, ideal for PV application.