Development of a simple two-step lithography fabrication process for resonant tunneling diode using air-bridge technology

This article reports on the development of a simple two-step lithography process for double barrier quantum well(DBQW)InGaAs/AlAs resonant tunneling diode(RTD)on a semi-insulating indium phosphide(InP)substrate using an air-bridge technology.This approach minimizes processing steps,and therefore the processing time as well as the required resources.It is particularly suited for material qualification of new epitaxial layer designs.A DC performance comparison between the proposed process and the conventional process shows approximately the same results.We expect that this novel technique will aid in the recent and continuing rapid advances in RTD technology.

GaAs-based resonant tunneling diode:Device aspects from design,manufacturing,characterization and applications

This review article discusses the development of gallium arsenide(GaAs)-based resonant tunneling diodes(RTD)since the 1970s.To the best of my knowledge,this article is the first review of GaAs RTD technology which covers different epitaxialstructure design,fabrication techniques,and characterizations for various application areas.It is expected that the details presented here will help the readers to gain a perspective on the previous accomplishments,as well as have an outlook on the current trends and future developments in GaAs RTD research.

Resonant tunneling and quantum fluctuation in a driven triple-well system

The influence of parameters such as the strength and frequency of a periodic driving force on the tunneling dynamics is investigated in a symmetric triple-well potential. It is shown that for some special values of the parameters, tunneling could be enhanced considerably or suppressed completely. Quantum fluctuation during the tunneling is discussed as well and the numerical results are presented and analysed by virtue of Floquet formalism.

Macroscopic resonant tunneling in an rf-SQUID flux qubit

We have observed the macroscopic resonant tunneling of magnetic flux between macroscopically distinct quantum states in a superconducting flux qubit. The dependences of the macroscopic resonant tunneling on the barrier height of the potential well, the flux bias and the initial state are investigated. Detailed measurements of the tunneling rate as a function of the flux bias reveal the feature of the quantum noise in the superconducting flux qubit.

Solid-state resonant tunneling thermoelectric refrigeration in the cylindrical double-barrier nanostructure

A solid-state thermoelectric refrigerator with a cylindrical InP/InAs/InP double-barrier heterostructure is proposed. Based on the ballistic electron transport and the asymmetrical transmission, we derive the expressions of the performance parameters of this refrigerator. The cooling rate rather than the coefficient of performance is affected by the area of the inner cylinder. Then through the numerical simulation, a triangular cooling rate region is found with respect to the chemical potential and bias voltage; further, that it is because of the small full width at half maximum of the transmission resonance and the linear relationship between the energy position of resonance and the bias voltage. These tunable results might supply some guide to the cooling in tiny components or devices.

Comparison of resonant tunneling diodes grown on freestanding GaN substrates and sapphire substrates by plasma-assisted molecular-beam epitaxy

AlN/GaN resonant tunneling diodes(RTDs)were grown separately on freestanding Ga N(FS-GaN)substrates and sapphire substrates by plasma-assisted molecular-beam epitaxy(PA-MBE).Room temperature negative differential resistance(NDR)was obtained under forward bias for the RTDs grown on FS-GaN substrates,with the peak current densities(Jp)of 175-700 kA/cm^(2)and peak-to-valley current ratios(PVCRs)of 1.01-1.21.Two resonant peaks were also observed for some RTDs at room temperature.The effects of two types of substrates on epitaxy quality and device performance of GaN-based RTDs were firstly investigated systematically,showing that lower dislocation densities,flatter surface morphology,and steeper heterogeneous interfaces were the key factors to achieving NDR for RTDs.

Resonant tunneling through double-barrier structures on graphene

Quantum resonant tunneling behaviors of double-barrier structures on graphene are investigated under the tightbinding approximation. The Klein tunneling and resonant tunneling are demonstrated for the quasiparticles with energy close to the Dirac points. The Klein tunneling vanishes by increasing the height of the potential barriers to more than 300 meV. The Dirac transport properties continuously change to the Schro¨dinger ones. It is found that the peaks of resonant tunneling approximate to the eigen-levels of graphene nanoribbons under appropriate boundary conditions. A comparison between the zigzag- and armchair-edge barriers is given.

Piezoelectric polarization and quantum size effects on the vertical transport in AlGaN/GaN resonant tunneling diodes

In this work,the electronic properties of resonant tunneling diodes（RTDs） based on GaN-AlxGa（1-x）N double barriers are investigated by using the non-equilibrium Green functions formalism（NEG）.These materials each present a wide conduction band discontinuity and a strong internal piezoelectric field,which greatly affect the electronic transport properties.The electronic density,the transmission coefficient,and the current–voltage characteristics are computed with considering the spontaneous and piezoelectric polarizations.The influence of the quantum size on the transmission coefficient is analyzed by varying GaN quantum well thickness,AlxGa1-xN width,and the aluminum concentration xAl.The results show that the transmission coefficient more strongly depends on the thickness of the quantum well than the barrier;it exhibits a series of resonant peaks and valleys as the quantum well width increases.In addition,it is found that the negative differential resistance（NDR） in the current–voltage（I–V） characteristic strongly depends on aluminum concentration xAl.It is shown that the peak-to-valley ratio（PVR） increases with xAlvalue decreasing.These findings open the door for developing vertical transport nitrides-based ISB devices such as THz lasers and detectors.

High-fidelity resonant tunneling passage in three-waveguide system

An N-stage three-waveguide system is proposed to improve the robustness and the fidelity of the resonant tunneling passage.The analytic solutions to the tunneling dynamics at the output are derived.When the number of subsystems increases,tunneling efficiency approaches to 100%in a large range and resonant tunneling is robust against variations in the phase mismatch and peak tunneling rate.

Macroscopic resonant tunneling in an rf-SQUID flux qubit under a single-cycle sinusoidal driving

We experimentally demonstrate the observation of macroscopic resonant tunneling（MRT） phenomenon of the macroscopic distinct flux states in a radio frequency superconducting quantum interference device（rf-SQUID） under a singlecycle sinusoidal driving.The population of the qubit exhibits interference patterns corresponding to resonant tunneling peaks between states in the adjacent potential wells.The dynamics of the qubit depends significantly on the amplitude,frequency,and initial phase of the driving signal.We do the numerical simulations considering the intra-well and interwell relaxation mechanism,which agree well with the experimental results.This approach provides an effective way to manipulate the qubit population by adjusting the parameters of the external driving field.

Spin injection in a ferromagnet/resonant tunneling diode heterostructure

The spin transport property of a ferromagnet （FM）/insulator （Ⅰ）/resonant tunneling diode （RTD） heterostructure was studied. The transmission coefficient and spin polarization in a multilayered heterostructure was calculated by a Schrdinger wave equation. An Airy function formalism approach was used to solve this equation. Based on the transfer matrix approach,the transmittivity of the structure was determined as a function of the Feimi energy and other parameters. The result shows that the spin polarization induced by the structure oscillates with the increasing Fermi energy of the FM layer. While the thickness of the RTD is reduced,the resonant peaks become broad. In the heterostructure,the spin polarization reaches as high as 40% and can be easily controlled by the external bias voltage.

Quantum Coupling Effect between Quantum Dot and Quantum Well in a Resonant Tunneling Photon-Number-Resolving Detector

Excited states of lnAs quantum dots （QDs） can be energetically coupled with the confined level of OaAs quantum wells （QWs） in a thin-barrier resonant tunneling diode （RTD）. Single charge variation in the coupled QD can effectively switch on/off the resonant tunneling current passing through RTD, not only for emcient single-photon detection but also for photon-number-resolving detection. We present the study of the Q,D-QW coupling effect in the quantum dot coupled resonant tunneling diode （QD-cRTD） and figure out important factors for further improving the detector performance.

Generation and Shaping of Soliton-Like Pulses along Resonant Tunneling Diodes NMOS Varactors Lattice

The characteristics of N-type accumulation-mode MOS (NMOS) varactors line periodically loaded with resonant tunneling diodes (RTDs) are used for soliton-like pulses generation and shaping. The problem of wide pulse breaking up into multiple pulses rather than a single is solved. Applying perturbative analysis, we show that the dynamics of the nonlinear transmission line (NLTL) is reduced to expanded Korteweg-de Vries (KdV) equation. Moreover, numerical integration of nonlinear differential and difference equations that result from the mathematical analysis of the line is discussed. As results, NLTL can simultaneously sharpen both leading and trailing of pulse edges and one could obtain a rising and sharpening step pulse.

Design of ternary D flip-flop with pre-set and pre-reset functions based on resonant tunneling diode literal circuit

The problems existing in the binary logic system and the advantages of multiple-valued logic (MVL) are introduced. A literal circuit with three-track-output structure is created based on resonant tunneling diodes (RTDs) and it has the most basic memory function. A ternary RTD D flip-flop with pre-set and pre-reset functions is also designed, the key module of which is the RTD literal circuit. Two types of output structure of the ternary RTD D flip-flop are optional: one is three-track and the other is single-track; these two structures can be transformed conveniently by merely adding tri-valued RTD NAND, NOR, and inverter units after the three-track output. The design is verified by simulation. Ternary flip-flop consists of an RTD literal circuit and it not only is easy to understand and implement but also provides a solution for the algebraic interface between the multiple-valued logic and the binary logic. The method can also be used for design of other types of multiple-valued RTD flip-flop circuits.

Improving the peak current density of resonant tunneling diode based on InP substrate

Resonant tunneling diodes（RTD）have the potential for compact and coherent terahertz（THz）sources operating at room temperature,but their low output power severely restricts their application in THz frequency range.In this paper,two methods are adopted to increase the peak current of RTD for enhancing its output power.First,different metal contact systems（including Pt/Ti/Pt/Au and Au Ge/Ni/Au）for RTD contact are introduced,and a higher current of RTD with Pt/Ti/Pt/Au contact demonstrates the superior contact characteristic of Pt/Ti/Pt/Au contact system.Second,the double barrier structure（DBS）of RTD is well designed to further improve the characteristic of RTD,and a high peak current of 154 kA/cm^2 is achieved at room temperature.The improved peak current is very beneficial for increasing the output power of RTD oscillator.

High peak-to-valley current ratio In_(0.53)Ga_(0.47)As/AlAs resonant tunneling diode with a high doping emitter

An In0.53Ga0.47As/AlAs resonant tunneling diode （RTD） with a high doping emitter is designed and fabricated using air bridge technology. The RTD exhibits a high peak-to-valley current ratio （PVCR） of more than 40 at room temperature, with a peak current density of 24 kA/cm2. The extraction of device parameters from DC and microwave measurements is presented together with an RTD equivalent circuit. The high PVCR RTD with small intrinsic capacitance is favorable for microwave/THz applications.

A Generalized Stationary Algorithm for Resonant Tunneling:Multi-Mode Approximation and High Dimension

The multi-mode approximation is presented to compute the interior wave function of Schr¨odinger equation.This idea is necessary to handle the multi-barrier and high dimensional resonant tunneling problems where multiple eigenvalues are considered.The accuracy and efficiency of this algorithm is demonstrated via several numerical examples.

The design and fabrication on gate type resonant tunneling transistor

In light of fabricating resonant tunneling diode(RTD),in this paper a GaAs-based resonant tunneling transistor with gate structure(GRTT)has been designed and fabricated successfully.A systematic depiction centers on the designs of material structure,device structure,photo-lithography mask,fabrication of device and the measurement and analysis of parameters.The fabricated GRTT has a maximum PVCR of 46 and a maximum transconductance of 8 mS.The work lays the foundation for further improve-ment on the performance and parameters of RTT.

Characteristics of cylindrical surrounding-gate GaAs_xSb_(1-x)/In_yGa_(1-y)As heterojunction tunneling field-effect transistors

A Ⅲ-Ⅴ heterojunction tunneling field-effect transistor(TFET) can enhance the on-state current effectively,and GaAsSb/InGaAs heterojunction exhibits better performance with the adjustable band alignment by modulating the alloy composition.In this paper,the performance of the cylindrical surrounding-gate GaAsSb/InGaAs heterojunction TFET with gate-drain underlap is investigated by numerical simulation.We validate that reducing drain doping concentration and increasing gate-drain underlap could be effective ways to reduce the off-state current and subthreshold swing(SS),while increasing source doping concentration and adjusting the composition of GaAsSbInGaAs can improve the on-state current.In addition,the resonant TFET based on GaAsSb/InGaAs is also studied,and the result shows that the minimum and average of SS reach 11 mV/decade and 20 mV/decade for five decades of drain current,respectively,and is much superior to the conventional TFET.

A novel micro-accelerometer with adjustable sensitivity based on resonant tunnelling diodes

Resonant tunnelling diodes （RTDs） have negative differential resistance effect, and the current-voltage characteristics change as a function of external stress, which is regarded as mesc-piezoresistance effect of RTDs. In this paper, a novel micro-accelerometer based on AlAs/GaAs/In0.1Ga0.9As/GaAs/AlAs RTDs is designed and fabricated to be a four-beam-mass structure, and an RTD-Wheatstone bridge measurement system is established to test the basic properties of this novel accelerometer. According to the experimental results, the sensitivity of the RTD based micro-accelerometer is adjustable within a range of 3 orders when the bias voltage of the sensor changes. The largest sensitivity of this RTD based miero-accelerometer is 560.2025 mV/g which is about 10 times larger than that of silicon based micro piezoresistive accelerometer, while the smallest one is 1.49135 mV/g.