Al0.3Ga0.7As-GaAs microwave resonant tunneling oscillator

We describe the design of a microwave oscillator using resonant tunneling diodes. The devices are fabricated from Al_0.3Ga_0.7As-GaAs double barrier hetero-structures grown by molecular beam epitaxy. Design criteria improving current drivability are established from a theoretical study of tunneling transmission probabilities. Very high peak current densities up to 3.10⁴ A/cm², favorable for high frequency operation as an oscillator, have been achieved experimentally. The devices exhibit stable oscillations at liquid nitrogen temperature and at room temperature when the tunnel diode oscillator is constructed with a stabilizing network.     

1.7-ps, microwave, integrated-circuit-compatible InAs/AlSb resonanttunneling diodes

Microwave integrated-circuit-compatible InAs/AlSb resonant tunneling diodes (RTDs) have been fabricated. The resulting devices have peak current densities of 3.3×10⁵ A/cm² with peak-to-valley ratios of 3.3. Switching transition times of 1.7 ps are measured using electrooptic sampling techniques     

Measurement of Enhanced Gate-Controlled Band-to-Band Tunneling in Highly Strained Silicon-Germanium Diodes

Strained silicon-germanium (Si_0.6Ge_0.4) gated diodes have been fabricated and analyzed. The devices exhibit significantly enhanced gate-controlled tunneling current over that of coprocessed silicon control devices. The current characteristics are insensitive to measurement temperature in the 80 K to 300 K range. Independently extracted valence band offset at the strained Si_0.6Ge_0.4/Si interface is 0.4 eV, yielding a Si_0.6Ge_0.4 bandgap of 0.7 eV, which is much reduced compared to that of Si. The results are consistent with device operation based on quantum-mechanical band-to-band (BTB) tunneling rather than on thermal generation. Moreover, simulation of the strained Si_0.6Ge_0.4 device using a quantum-mechanical BTB tunneling model is in good agreement with the measurements.     

Thin film pseudomorphicAlAs/In0.53Ga0.47As/InAs resonant tunnellingdiodes integrated onto Si substrates

We report high peak-to-valley current ratio (PVR) resonant tunneling diodes (RTDs) bonded to silicon. Pseudomorphic AlAs/In_0.53Ga_0.47As/InAs resonant tunneling diode structures grown on semi-insulating InP with peak-to-valley current ratios as high as 30 at 300 K have been separated from the growth substrate and bonded to silicon substrates coated with Si₃N ₄, forming thin film devices. In addition, thin film multiple stack RTD structures have been bonded to silicon substrates. The I-V characteristics of both the single and multi-stacked thin film RTD's exhibit no signs of degradation after bonding to the host substrate. These results are the first successful demonstration of InP based electronics bonded to a silicon host substrate and enable the integration of RTDs with conventional silicon circuitry     

Fabrication of 200-GHz fmax resonant-tunnelingdiodes for integration circuit and microwave applications

Room-temperature current densities of 1.3×10⁵ A/cm² and peak-to-valley ratios of 2.5 have been achieved for resonant tunneling diodes (RTDs) in the GaAs/AlAs material system. The devices were fabricated in a microwave-compatible process using topside contacts and a semi-insulating substrate to allow device integration. Proton implantation creates a nonconducting surface compatible with high-frequency coplanar transmission lines and other passive microwave structures     

P-N double quantum well resonant interband tunneling diode withpeak-to-valley current ratio of 144 at room temperature

The current-voltage characteristics of the P-N double quantum well resonant interband tunneling (RIT) diodes in InAlAs-InGaAs system have been improved in this letter. The peak-to-valley current ratio (PVCR) is as high as 144 at room temperature. As we know, this is the highest room temperature PVCR ever reported in any tunneling devices. Moreover, the influence of the central barrier thickness varying from 10 Å to 30 Å on the device characteristics is also studied     

On Charge Transport and Low-Frequency Noise in the GaN p-i-n Diode

The current-voltage (I-V) characteristics and low-frequency noise of the GaN p-i-n diodes were investigated in temperature range from 10 K to 300 K. We found that the reverse biased p-i-n diode made of GaN/AlGaN exhibits features of the space charge limited (SCL) current flow and its I-V characteristics can be approximated by the power law I~Vⁿ relation. This phenomenon can be attributed to the presence of the multiple charge traps in the intrinsic region of device. It has been demonstrated that the direct tunneling from traps to bands may occur in diodes at forward and reverse bias with strong support of the Frenkel effect. The low frequency noise in our devices does not depend on temperature in both bias directions under cryogenic conditions. The observed low-frequency noise features support the hypothesis that excess tunneling current and recombination at grain boundaries are origins of the 1/f low-frequency noise in the diode at forward bias. The 1/f noise in the reverse bias regime can be described as a composition of many Lorentzian noise components that originate from traps, which have specific depth distribution     

Bulk tunneling contribution to the reverse breakdown characteristics of InSb gate controlled diodes

This work presents measurements and analysis of optimized reverse breakdown characteristics of InSb p⁺n gate controlled mesa diodes. Surface current contributions were minimized by adjusting the potential of the peripheral gate electrode. The resulting measured breakdown currents are found to be proportional to the junction area and exhibit diode bias and temperature dependence that fit quantitatively to direct band-to-band tunneling theory of one sided abrupt junction devices. The agreement between theory and experiment, achieved without any fitting parameter, confirms that bulk band-to-band direct tunneling mechanism is the fundamental limit for the diodes reverse bias performance.     

Deep levels at p-n and n-p AlGaAs-GaAs heterojunction interfaces

Forward current-voltage measurements and DLTS spectra were obtained for p^--n and n^--p Al0.3Ga0.7As-GaAs heterodiodes. The current-voltage measurements support a tunneling current model for the p^--n diodes and a diffusion-recombination current model for the n^--p diodes. No deep levels were observed for the p^--n structure, but two new levels at about 0.1 and 0.4 eV below the conduction band edge, and possibly zinc related, were found in the n^--p devices.     

Quantum transistors and circuits break through the barriers

Resonant tunneling diodes and transistors, which are `vertical' quantum devices, in which the current flows perpendicular to the layers instead of along them, are discussed. The operation of both devices is explained. Various types of resonant tunneling transistor are examined, with particular attention to multistate devices. Applications to frequency multipliers, parity generators, and analog-to-digital converters are presented     

Spatial integration of direct band-to-band tunneling currents ingeneral device structures

A simplified integration technique for direct band-to-band tunneling current calculation in semiconductor devices of 1- or 2-D general device structures is described. The integration, along part of the depletion region, is of a tunneling generation function which depends on the local electric field. The simplified integration scheme relies on Kane's parabolic shaped gap barrier which accurately applies to such narrow-bandgap semiconductors as InSb and Hg_1-xCd_xTe. Tunneling current and zero bias resistance calculations in 1-D Hg_1-xCd_xTe p-n junctions using the proposed technique are presented. The extension of the technique to 2-D potential structures is demonstrated by modeling peripheral surface tunneling currents. The results compare well with measured reverse breakdown currents of InSb gate-controlled diodes     

纳米电子器件及其集成

对基于Top-Down加工技术的纳米电子器件如：单电子器件、共振器件、分子电子器件等的研究现状、面临的主要挑战等进行了讨论. 采用CMOS兼容的工艺成功地研制出单电子器件，观察到明显的库仑阻塞效应；在半绝缘GaAs衬底上制作了AlAs/GaAs/In0.1Ga0.9As/GaAs/AlAs双势垒共振隧穿二极管,采用环型集电极和薄势垒结构研制的共振隧穿器件，在室温下测得其峰谷电流比高达13.98，峰电流密度大于89kA/cm2；概述了交叉阵列的分子存储器的研究进展.     

Oxide roughness effect on tunneling current of MOS diodes

Two-dimensional (2-D) device simulation is used to investigate the tunneling current of metal ultra-thin-oxide silicon tunneling diodes with different oxide roughness. With the conformal nature of ultrathin oxide, the tunneling current density is simulated in both direct tunneling and Fowler-Nordheim (FN) tunneling regimes with different oxide roughness. The results show that oxide roughness dramatically enhances the tunneling current density and the 2-D electrical effect is responsible for this increment of tunneling current density. Furthermore, a set of devices with controlled oxide roughness is fabricated to verify the simulation results and our model qualitatively agrees with the experiment results.     

纳米电子器件-高峰值峰谷电流比InP基共振隧穿二极管的实现

利用分子束外延技术研制出InP基IhAs/In0.53Ga0.47As/AlAs共振隧穿二极管,其中势垒为10个单分子AlAs,势阱由8个单分子层In0.53Ga0.47As阱和4个单分子层InAs子阱组成.室温下峰值电流密度接近3kA/cm2,峰和谷的电流密度比率达到19.     

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.     

InGaN／AlGaN双异质结构蓝光LED的电学和光学性质

研究了ＩｎＧａＮ／ＡｌＧａＮ双异质结构（ＤＨ）蓝光发光二极管（ＬＥＤ）的电学和光学性质，实验表明，器件正向偏压下的Ｉ－Ｖ特性偏离了ｐｎ结二极管的肖克莱模型的结果，并且载流子的主要输运机制与载流子隧穿有关。通过对电致发光（ＥＬ）谱的测量，得到位于２．８ｅＶ的发射峰和位于３．２ｅＶ弱发射峰，随着电流增大而均出现蓝移。对大脉冲电流下ＬＥＤ的特性的退化作了研究。     

Roughness-enhanced reliability of MOS tunneling diodes

Both electrical and optical reliabilities of PMOS and NMOS tunneling diodes are enhanced by oxide roughness, prepared by very high vacuum prebake technology. For rough PMOS devices, as compared to flat PMOS devices, the Weibull plot of T_BD shows a 2.5-fold enhancement at 63% failure rate, while both the D₂ and H₂-treated flat PMOS devices show similar inferior reliability. For rough NMOS devices, as compared to flat NMOS devices, the Weibull plot of T_BD shows a 4.9-fold enhancement at 63% failure rate. The time evolutions of the light emission from rough PMOS and NMOS diodes degrade much less than those of flat PMOS and NMOS diodes. The momentum reduction perpendicular to the Si/SiO₂ interface by roughness scattering could possibly make it difficult to form defects in the bulk oxide and at the Si/SiO₂ interface by the impact of the energetic electrons and holes     

Numerical simulation of the current-voltage characteristics ofheteroepitaxial Schottky-barrier diodes

A numerical model resulting in the current-voltage characteristics of standard and heteroepitaxial Schottky-barrier diodes is presented. Simulations of GaAs diodes, as well as InGaAs diodes grown on GaAs and InP substrates, are presented. The model considers quantum-mechanical tunneling, and is therefore applicable to highly doped devices. A self-consistent drifted-Maxwellian distribution is used to model the electron energy distribution at high current densities. The assumption of a drifted-Maxwellian distribution is shown to lead to higher current at high bias than predicted with the assumption of a Maxwell-Boltzmann or Fermi-Dirac distribution. The presence of a heterojunction at the InGaAs-substrate interface is predicted to lead to an additional series resistance component     

Digital circuit applications of resonant tunneling devices

Many semiconductor quantum devices utilize a novel tunneling transport mechanism that allows picosecond device switching speeds. The negative differential resistance characteristic of these devices, achieved due to resonant tunneling, is also ideally suited for the design of highly compact, self-latching logic circuits. As a result, quantum device technology is a promising emerging alternative for high-performance very-large-scale-integration design. The bistable nature of the basic logic gates implemented using resonant tunneling devices has been utilized in the development of a gate-level pipelining technique, called nanopipelining, that significantly improves the throughput and speed of pipelined systems. The advent of multiple-peak resonant tunneling diodes provides a viable means for efficient design of multiple-valued circuits with decreased interconnect complexity and reduced device count as compared to multiple-valued circuits in conventional technologies. This paper details various circuit design accomplishments in the area of binary and multiple-valued logic using resonant tunneling diodes (RTD's) in conjunction with high-performance III-V devices such as heterojunction bipolar transistors (HBT's) and modulation doped field-effect transistors (MODFET's). New bistable logic families using RTD+HBT and RTD+MODFET gates are described that provide a single-gate, self-latching majority function in addition to basic NAND, NOR, and inverter gates     

不同钝化结构的HgCdTe光伏探测器暗电流机制

在同一HgCdTe晶片上制备了单层ZnS钝化和双层（CdTe+ZnS）钝化的两种光伏探测器,对器件的性能进行了测试,发现双层钝化的器件具有较好的性能．通过理论计算,分析了器件的暗电流机制,发现单层钝化具有较高的表面隧道电流．通过高分辨X射线衍射中的倒易点阵技术研究了单双层钝化对HgCdTe外延层晶格完整性的影响,发现单层ZnS钝化的HgCdTe外延层产生了大量缺陷,而这些缺陷正是单层钝化器件具有较高表面隧道电流的原因．