Gunn Diode Research Articles

Avoiding avalanche breakdown in planar GaN Gunn diodes by means of a substrate contact

Abstract Impact ionization originated by the buffer leakage current, together with high electric fields ( > 3 MV cm−1) at the anode corner of the isolating trenches, has been identified as the failure mechanism of shaped planar GaN Gunn diodes when biased above 20 V, so that no evidence of Gunn oscillations in fabricated devices has been observed yet. In order to avoid the avalanche, we propose the addition of a Schottky substrate terminal, which, by means of Monte Carlo simulations, has been confirmed to be able to suppress such not-desired leakage current when applying a negative substrate bias. When the substrate bias is positive, impact ionization is also reduced due to the lower electric field at the hotspot, but a vertical cathode-substrate current degrades the device operation. In order to avoid such current, we propose the use a MIS configuration for the substrate contact, which is the optimal solution.

Monte Carlo Study of Gunn Oscillations in Geometrically Shaped Planar Gunn Diodes Based on Doped GaN: Influence of Geometry, Intervalley Energy, and Temperature

Monte Carlo Study of Gunn Oscillations in Geometrically Shaped Planar Gunn Diodes Based on Doped GaN: Influence of Geometry, Intervalley Energy, and Temperature

Research on the Gunn Oscillation Effect of GaN HEMT with Field Plate Structure in the Terahertz Frequency Band

Research on the Gunn Oscillation Effect of GaN HEMT with Field Plate Structure in the Terahertz Frequency Band

N-type semiconductor with energy storage made from chitosan

Chitosan, obtained from crustaceans such as crabs and shrimp, has been mainly used in medicine; however, no studies on its use in electronic applications with semiconducting and large storage properties have been reported. Here, we report an n-type semiconducting biomaterial with energy storage properties of 694.4 mJ/m2 consisting of a chitosan nanofiber (ChNF) film with N-type negative resistance. The ChNF generates an alternative-current wave with a frequency of 7.8 MHz at a threshold voltage of 187 MV/m from a direct-current voltage source, with the switching effect of a third-order resistance change. This is due to the Gunn effect, caused by the repeated voltage-induced generation of a strong electric field domain (electric double layer) at the cathode and its disappearance at the anode of the ChNF device. Electron spin resonance spectral analysis showed that conducting electrons of the ChNF were identified as radicals on the aminyl radical, N·H. Paper electronics made from marine products are a great boon to a renewable society.

Radiation Hardness of Subterahertz Radiation Source Based on Heterodyne on Gunn Diode Generator and Superlattice Multiplier

Radiation Hardness of Subterahertz Radiation Source Based on Heterodyne on Gunn Diode Generator and Superlattice Multiplier

Negative differential resistors from carbon-based cryogels incorporating graphene oxide into a ferroelectric polymer matrix

Electronic components with negative differential resistance (NDR) are essential in power electronics to build Gunn diodes, varactors, parametric amplifiers and switching circuits. However, their implementation through silicon-based electronics is costly and demands complex circuitry and components. Here, we introduce for the first time a class of hybrid carbon-based and organic aerogels, prepared at liquid nitrogen temperature (77 K) by a simple and scalable freeze-drying method. These cryogels exhibit NDR. In these cryogels, the carbonaceous phase is represented by d-glucose-graphene oxide nanocomposites while the organic phase is represented by polyvinylidene difluoride (PVDF), a ferroelectric polymer. NDR in our samples is assigned to the local electric field effects of PVDF on the charge carriers of more electrically conducting graphene oxide and d-glucose. Through an operando study via scanning near-field optical microscopy, we also show that low thermal expansion and low thermal conductivity are essential to prevent undesired effects in our devices through parasitic capacitance's discharge.

Caputo-fabrizio fractional-order systems: periodic solution and stabilization of non-periodic solution with application to gunn diode oscillator

Fractional-order autonomous systems do not possess any non-constant periodic solutions, and to the best of our knowledge, there are no existing results regarding the existence of the periodic solution for fractional-order non-autonomous systems. The main objective of this work is to fill the above gap by studying the existence of a periodic solution of the Caputo-Fabrizio fractional-order system and also to find ways to stabilize a non-periodic solution. First, by using the concepts of an equilibrium point, it is proved that an autonomous Caputo-Fabrizio system cannot admit a non-constant periodic solution. Under a similar assumption as the one for an integer-order differential system, and by using the properties of the Caputo-Fabrizio derivative, the existence of a periodic solution of a non-autonomous Caputo-Fabrizio fractional-order differential system is established. The main result is utilized in constructing and finding the periodic solution of the linear non-homogeneous Caputo-Fabrizio system. By using the result on linear systems, we derive a periodic solution of a fractional-order Gunn diode oscillator under a periodic input voltage, and observe that the diameter of the periodic orbit keeps reducing as the fractional-order continuously increases. In the end, by using the result on a linear non-homogeneous system, and by constructing a suitable linear feedback control, the solution of the linear non-homogeneous fractional-order system is stabilized to a periodic solution. An example is presented to support the obtained result. The main advantage of the proposed method over others is the simple considerations like the concept of equilibrium point and the utilization of the property of the Caputo-Fabrizio derivatives instead of other types of fractional derivatives.

Photoinduced Negative Differential Resistivity and Gunn Oscillations in SrTiO3.

SrTiO3 , a perovskite oxide, holds significant potential for application in the field of oxide electronics. Notably, its photoelectric activity in the low temperature regime, which overlaps with the quantum paraelectric state, exhibits remarkable characteristics. In this study, it is demonstrated that when photo-excited with above band gap energy photons, SrTiO3 exhibits non-linear transport of photocarriers and voltage-controlled negative resistance, resulting from an intervalley transfer of photo-induced electrons. As a consequence of the negative resistance, the photocurrent becomes unstable and spontaneously gives rise to low frequency Gunn-like oscillations.

Power-frequency performance of step-graded double Gunn diodes

Simulations of conventional Gunn diodes containing the double Gunn effect have shown a significant increase in oscillation frequency and frequency range. However, conventional Gunn diodes suffer from higher phase noise, lower efficiency, and reduced temperature stability due to the lack of a hot electron injector. A study on the performance of a Double Gunn diode with a graded gap injector is presented. The second region of negative differential mobility is gradually introduced in several temperature-dependent mobility models, which are implemented in an energy balance simulation. Devices with transit lengths of 0.7μm, 1.1μm, and 1.65μm are simulated. All devices experience an increase in oscillation frequency with increasing intensities of the double Gunn effect. The frequency range doubles at significant intensities of the effect in the devices with transit lengths of 0.7μm and 1.65μm.

On the Practical Limitations for the Generation of Gunn Oscillations in Highly Doped GaN Diodes

Planar Gunn diodes based on doped GaN active layers with different geometries have been fabricated and characterized. Gunn oscillations have not been observed due to the catastrophic breakdown of the diodes for applied voltages around 20–25 V, much below the bias theoretically needed for the onset of Gunn oscillations. The breakdown of the diodes has been analyzed by pulsed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}$</tex-math> </inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{V}$</tex-math> </inline-formula> measurements at low temperatures, and it has been observed to be almost independent of the geometry of the channels, thus allowing to discard self-heating effects as the origin of the device burning. The other possible mechanism for the device failure is an impact-ionization avalanche due to the high electric fields present at the anode corner of the isolating trenches. However, Monte Carlo simulations using the typical value of the intervalley energy separation of GaN, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon_{\text{1}-\text{2}}$</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$=$</tex-math> </inline-formula> 2.2 eV, show that impact ionization mechanisms are not significant for the voltages for which the experimental failure is observed. But recent experiments showed that <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon_{\text{1}-\text{2}}$</tex-math> </inline-formula> is lower, around 0.9 eV. This lower intervalley separation leads to a much lower threshold voltage for the Gunn oscillations, not far from the experimental breakdown. Therefore, we attribute the device’s failure to an avalanche process just when Gunn domains start to form, since they increase the population of electrons at the high electric field region, thus strongly enhancing impact ionization mechanisms that lead to the diode failure.

Анализ и разработка высокоточного генератора частоты w-диапазона с низким уровнем паразитных гармоник

For millimeter waves applications in the W-band 93.5-95.5 GHz, improved frequency synthesizers are highly demanded. Improved frequency synthesizer should be tunable synthesizer with high step resolution and possess high phase noise performance, low spurious harmonic levels and short locking time. These parameters are conflicting parameters in developing a high precision frequency oscillator with a pure spectrum. Therefore, it's necessary to make a compromisation between them. In this paper we present a frequency synthesizer based on a Gunn diode, two stable finely tuned frequency sources, a phase locked loop, and a 10th order subharmonic mixer in the feedback loop is built. The phase noise, spurious levels, and tuning step size of the phase locked loop generator are then analyzed, and the effect of each parameter on the others is introduced. To test the performance of the proposed frequency synthesizer using a spectrum analyzer, the output spectrum of the intermediate frequency was measured on a subharmonic mixer, which corresponds to the spectrum of a phase-locked loop generator. The results show that the proposed phase-locked loop generator can be tuned in steps of less than 1 Hz, and the first two spurious harmonics are far from the fundamental harmonic. These results can be used for designing an enhanced high precision frequency synthesizer with a low level of spurious harmonics and high phase noise performance in millimeter waves applications such as CW RADAR.

Measurement of optically-pumped electron spin polarization in n-GaAs at high external electric fields

We use the technique of time-resolved Kerr rotation (TRKR) to measure the electron spin polarization generated by optical spin pumping in an n-type gallium arsenide (GaAs) epilayer when an external electric field is simultaneously applied on the sample. The drift of the electron spins under the influence of the external electric field is captured with spatial scans of the pump–probe separation. A significant decay in the magnitude of electron spin polarization with electric field is observed and is attributed to the increased inhomogeneous broadening caused by the field-induced drift and the hot electron effects. We extend the electric field range to as high as the Gunn threshold field in the measurement and we do not observe a spin amplification effect due to the spin Gunn effect under our experimental scheme.

Three‐state pattern reconfigurable active antenna integrated with Gunn oscillator and switched‐line phase shifter

AbstractIn this paper, a novel active integrated array antenna (AIAA) is introduced for the purpose of enabling pattern switchable functionality. The AIAA includes a Gunn oscillator, four microstrip antennas, and two switched‐line phase shifters. The Gunn oscillator provides high‐output RF power to excite the antenna elements through the switched‐line phase shifters. The switched‐line phase shifter allows for switching the main beam direction of the radiation pattern among three states, specifically , and in the ‐plane without shifting its high resonance frequency. Besides, the AIAA requires fewer RF switching diodes in a compact, cheap, and simple layout when compared to previously reported AIAAs. An experimental evaluation of the proposed antenna's performance is conducted and the results indicate an effective isotropic radiated power (EIRP) of +16.09 dBm at the frequency of 9.41 GHz. In all three states, the cross‐polarization suppression is better than 15 dB.

A Deep Learning-Monte Carlo Combined Prediction of Side-Effect Impact Ionization in Highly Doped GaN Diodes

The existence of leakage current pathways leading to the appearance of impact ionization and the potential device breakdown in planar Gunn GaN diodes is analyzed by means of a combined Monte Carlo (MC)-deep learning approach. Front-view (lateral) MC simulations of the devices show the appearance of a high-field hotspot at the anode corner of the etched region, just at the boundaries between the dielectric, the GaN-doped layer, and the buffer. Thus, if the isolation created by the etched trenches is not complete, a relevant hot carrier population within the buffer is observed at sufficiently high applied voltages, provoking the appearance of a very significant number of impact ionizations and the consequent avalanche process before the onset of Gunn oscillations. A neural network trained from MC simulations allows predicting with extremely good precision the breakdown voltage of the diodes depending on the doping of the GaN active layer, the permittivity of the isolating dielectric, and the lattice temperature. Low doping, high temperature, and high permittivity provide larger operational voltages, which implies a tradeoff with the conditions required to achieve terahertz (THz) Gunn oscillations at low voltages.

Sub-terahertz scanning near-field optical microscope using a quartz tuning fork based probe.

We report a sub-terahertz scattering-type scanning near-field microscope (sub-THz s-SNOM) which uses a 6 mm long metallic tip driven by a quartz tuning fork as the near-field probe. Under continuous-wave illumination by a 94 GHz Gunn diode oscillator, terahertz near-field images are obtained by demodulating the scattered wave at both the fundamental and the second harmonic of the tuning fork oscillation frequency together with the atomic-force-microscope (AFM) image. The terahertz near-field image of a gold grating with a period of 2.3 µm obtained at the fundamental modulation frequency agrees well with the AFM image. The experimental relationship between the signal demodulated at the fundamental frequency and the tip-sample distance is well fitted with the coupled dipole model indicating that the scattered signal from the long probe is mainly contributed by the near-field interaction between the tip and the sample. This near-filed probe scheme using quartz tuning fork can adjust the tip length flexibly to match the wavelength over the entire terahertz frequency range and allows for operation in cryogenic environment.

ИСПОЛЬЗОВАНИЕ ОРТОГОНАЛЬНЫХ СИЛЬНЫХ ЭЛЕКТРИЧЕСКИХ И МАГНИТНЫХ ПОЛЕЙ ДЛЯ СОЗДАНИЯ ЧАСТОТНО-ПРЕОБРАЗОВАТЕЛЬНЫХ УСТРОЙСТВ АВТОДИННОГО ТИПА

In the framework of the drift-diffusion model of carrier transport in the bulk of III–V typesemiconductors, under external action of strong constant electric and magnetic fields orthogonallyoriented relative to each other, a new principle for applying the discovered effects is proposed, whichtake into account the nonlinearities of the output parameters of the working chip, which leads to thepossibility creation of new semiconductor structures controlled by a magnetic field (SSCMF). Previously,the diffusion component of the output current density was not taken into account as a separateeffect arising under the orthogonal action of strong electric and magnetic components, which was atfirst time considered in this paper. It is shown that this component is a part of the inductive transverseoutput current and can be considered as an independent effect. The proposed practical applicationis based on the classical relations that describe the component spatial representation of the effectivemass energy dependence and the parameters of the kinetic equations for the carriers drift andheating in the bulk of highly mobile III–V type semiconductors structures. (The energy dependence ofthe reciprocal effective mass value was obtained under the assumption that this parameter becomesheavier in the framework of the two-valley representation. However, the mechanism of such increasingis not considered in detail, but is taken into account as a result of expansion in a Taylor series.)At the same time, some new phenomena were also hypothetically discovered: a diffusion detectoreffect and a transverse induction effect controlled by a magnetic field, similar in its manifestation tothe Gunn effect observed in this direction. The results obtained open the prospect for creating fundamentallynew frequency-converting devices based on the above SSCMF, such as autodyne-type converters(mixers), one of the designs of which is also proposed in this work in a waveguide version. Inthe case of experimental confirmation of the discovered effects, which can be investigated using theblock diagram of the measuring setup proposed in the work, we can conclude that there are promisingnew applications of magnetically controlled semiconductor structures. In addition, equipmentdevelopers will be interested in the possibility of using the magnetic field orientation angle to controlthe output parameters of such structures as part of converters

Notch-δ-doped InP Gunn diodes for low-THz band applications

The viability of the indium phosphide (InP) Gunn diode as a source for low-THz band applications is analyzed based on a notch-δ-doped structure using the Monte Carlo modeling. The presence of the δ-doped layer could enhance the current harmonic amplitude (A0) and the fundamental operating frequency (f0) of the InP Gunn diode beyond 300 ​GHz as compared with the conventional notch-doped structure for a 600-nm length device. With its superior electron transport properties, the notch-δ-doped InP Gunn diodes outperform the corresponding gallium arsenide (GaAs) diodes with up to 1.35 times higher in f0 and 2.4 times larger in A0 under DC biases. An optimized InP notch-δ-doped structure is estimated to be capable of generating 0.32-W radio-frequency (RF) power at 361 ​GHz. The Monte Carlo simulations predict a reduction of 44% in RF power, when the device temperature is increased from 300 ​K to 500 ​K; however, its operating frequency lies at 280 ​GHz which is within the low-THz band. This shows that the notch-δ-doped InP Gunn diode is a highly promising signal source for low-THz sensors, which are in a high demand in the autonomous vehicle industry.

Flexible terahertz optics: light beam profile engineering via C-shaped metallic metasurface

The potential of terahertz (THz) imaging implementation in a large variety of applications requires compact, reliable, and relatively low-cost solutions in systems constituents. Here we focus on the development of passive optical elements and demonstrate flexible and reliable THz beam profile engineering for imaging aims via mechanical bending of a stainless steel-based C-shaped metasurface. The designed and laser-ablation technology fabricated metasurface provides compact THz focusing and enables THz light engineering as well as polarization control ability in THz imaging. Focusing, light profile engineering, and polarization control performances of the metasurfaces with different focal distances and C-shape designs are presented. Experimental data are well supported by simulations, using Finite Difference Time Domain (FDTD) method. THz images of different objects at ∼94 GHz using InP Gunn diode, bow-tie sensors, and exclusively metasurfaces-based optics are exposed. Further routes in the development of low-cost multicolor and polarization-sensitive THz imaging are discussed.

Enhanced InP-based Gunn Diodes with Notch-d-doped Structure for Low-THz Applications

In this work, Monte Carlo simulation is performed for InP Gunn diode with a notch-d-doped structure. It is found that the presence of the d-doped layer has improved the Gunn diode performance significantly as compared to the conventional notch structure. The d-doped effect caused an increment in the fundamental operating frequency and current harmonic amplitude in InP Gunn diodes by modifying the electric field profile within the device. An InP notch-d-doped Gunn diode with device length of 800 nm under 3V DC bias is capable of producing AC current signal of 287 GHz, reaching the THz region, with its harmonic amplitude being 5.68×108 A/m2. It is observed that InP-based notch-d-doped Gunn diode is able to generate signals at a higher operating frequency with a larger output power as compared to that of GaAs due to the higher electron drift velocity and threshold field in InP material.

The wideband tunability of double Gunn diodes

Gunn diodes use the Ridley–Watkins–Hilsum effect to generate low noise millimeter wave signals for communication and sensing applications. However, Monte Carlo calculations indicate that the velocity–field characteristics of compensated GaAs contain a second peak due to phonon scattering. A novel device that leverages this double Ridley–Watkins–Hilsum effect to achieve ultra-wideband tunability of low-noise millimeter waves is proposed in this article. The second region of negative differential mobility is gradually introduced in seven mobility profiles, which are each simulated in eight device lengths. It is found that a 2.5 μm Gunn diode with a compensation ratio of 0.6 operating at 160 K has a 700% increase in frequency tunability. An analysis of the domain formation indicates that the increase in tunability is due to significant distortions in domain shape. Gunn diodes with transit lengths of 2 μm and smaller show a 100% increase in tunability due to modulations in the effective transit length and absorption rate. These simulations indicate that compensated GaAs could provide linear, ultra-wideband frequency tunability.