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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. [ABSTRACT FROM AUTHOR]

By means of Monte Carlo simulations of gallium nitride (GaN) planar Gunn diodes, the epilayer structure on which they are fabricated is optimized in order to achieve ultrahigh-frequency oscillations. Practical considerations, such as the limitations of the technological fabrication process and the mitigation of the huge self-heating effects expected to appear in the devices, have been also contemplated for the choice of the optimal epilayer parameters. The best results are obtained for an active layer thickness of 150 nm with doping of 5 $\times 10^{{18}}$ cm−3, which would provide 350 GHz Gunn oscillations when using a contact separation of $0.5~\mu \text{m}$. [ABSTRACT FROM AUTHOR]

For the first time, Gallium Nitride(GaN)-based Gunn diodes with side-contact and fieldplate technologies were fabricated and measured with reliable characteristics. A high negative differential resistance (NDR) region was characterised for the GaN Gunn effect using side-contact technology. The I-V measurement of the THz diode showed the ohmic and the Gunn effect region with high forward current of 0.65 A and high current drop of approximately 100 mA for a small ring diode width wd of 1.5 μm with 600 nm effective diode height hd at a small threshold voltage of 8.5 V. This THz diode worked stable due to good passivation as protection from electro-migration and ionisation between the electrodes as well as a better heat sink to the GaN substrate and large side-contacts. The diodes can provide for this thickness a fundamental frequency in the range of 0.3 - 0.4 THz with reliable characteristics.

We present a numerical analysis on an ultra-short channel AlGaN/GaN HEMT-like planar Gunn diode based on the velocity-field dependence of two-dimensional electron gas (2-DEG) channel accounting for the ballistic electron acceleration and the inter-valley transfer. In particular, we propose a Schottky-ohmic composite contact instead of traditional ohmic contact for the Gunn diode in order to significantly suppress the impact ionization at the anode side and shorten the "dead zone" at the cathode side, which is beneficial to the formation and propagation of dipole domain in the ultra-short 2-DEG channel and the promotion of conversion efficiency. The influence of the surface donor-like traps on the electron domain in the 2-DEG channel is also included in the simulation. [ABSTRACT FROM AUTHOR]

The length of the transit region of a Gunn diode determines the natural frequency at which it operates in fundamental mode-the shorter the device, the higher the frequency of operation. The long-held view on Gunn diode design is that for a functioning device the minimum length of the transit region is about 1.5 μm, limiting the devices to fundamental mode operation at frequencies of roughly 60 GHz. Study of these devices by more advanced Monte Carlo techniques that simulate the ballistic transport and electron-phonon interactions that govern device behaviour, offers a new lower bound of 0.5 μm, which is already being approached by the experimental evidence that has shown planar and vertical devices exhibiting Gunn operation at 600 nm and 700 nm, respectively. The paper presents results of the first ever THz submicron planar Gunn diode fabricated in In0.53Ga0.47As on an InP substrate, operating at a fundamental frequency above 300 GHz. Experimentally measured rf power of 28 μW was obtained from a 600 nm long × 120 μm wide device. At this new length, operation in fundamental mode at much higher frequencies becomes possible-the Monte Carlo model used predicts power output at frequencies over 300 GHz. [ABSTRACT FROM AUTHOR]

Coupled longitudinal-optical (LO)-phonon-plasmon excitations were studied using confocal micro-Raman spectroscopy. The high-quality Si-doped GaN epilayers were grown in a Gunn diode structure on (0001) sapphire substrates by plasma assisted molecular beam epitaxy. Depth-profiled Raman spectra exhibit a spatial variation of both low, ω-, and high, ω+, frequency coupled phonon-plasmon modes (CPPMs) in the n-GaN layers. To describe the features of the CPPMs in the Raman spectra a self-consistent model that includes both the electro-optic and deformation-potential as well as charge-density fluctuation mechanisms as important processes for light scattering in n-GaN has been proposed. An agreement between the theoretical and experimental line shapes of the Raman spectra is obtained. From the best line-shape fitting of the CPPMs the depth profiles of the plasmon and phonon damping, plasmon frequency, free carrier concentrations, and electron mobility as well as the contributions of the electron-phonon interaction and charge density fluctuations to the Raman cross section in the GaN layers are determined. It is found that these depth profiles exhibit considerable nonuniformity and change at different laser pump-power excitations. Despite the high electron concentration in the n+-GaN layers, a strong peak of the unscreened A1(LO) phonon is also observed. A possible origin for the appearance of this mode is discussed. [ABSTRACT FROM AUTHOR]

The article describes the design of the heat sink on the basis of a multi-stage thermoelectric device implements a method for removing the heat of transformation of the environment by means of radiation through the use of Gunn diodes, which will increase and intensify the processes of heat transfer and energy efficiency of cooling systems.

Featured Application: This manuscript provides a simulation study on the self-heating effect of the GaN-based terahertz Gunn diode. It would potentially give some guidance to the design of the Gunn diode and other terahertz oscillators. The method in this manuscript can be also used to study the self-heating effect of other semiconductor devices. In this paper, a comprehensive evaluation of thermal behavior of the GaN vertical n+-n−-n-n+ Gunn diode have been carried out through simulation method. We explore the complex effects of various parameters on the device thermal performance through a microscopic analysis of electron movements. These parameters include operation bias, doping level, and length of the active region. The increase of these parameters aggravates the self-heating effect and degrades the electron domains, which therefore reduces the overall performance output of the diode. However, appropriate increase of the doping level of active region makes the lattice heat distribute more uniformly and improves the device performance. For the first time, we propose the transition domain, which is in between the dipole domain and accumulation layer, and stands for the degradation of the electron domain. We have also demonstrated that dual domains occur in the device with longer active region length and higher doping level under EB (Energy balance) model, which enhances the harmonics component. Electric and thermal behaviors analysis of GaN vertical Gunn diode makes it possible to optimize the device. [ABSTRACT FROM AUTHOR]

In this article, we present a short overview of the Ukrainian contribution into physics of 2D semiconductor structures as a basis for high-tech devices of modern nanoelectronics together with some new results in this field. The possibility of creating "low-threshold" 2D lasers in Si3N4-GaAs and AlxGa1-xAs-GaAs layered heterostructures, in which two-dimensional electron-hole plasma (EHP) is formed, has been analyzed. The investigations of optical amplification spectra in heterostructures with a two-dimensional quantum well have been performed in details. It has been demonstrated that under the conditions of simultaneous co-existence of 3D-EHP and 2D-EHP, stimulated radiation is formed predominantly in 2D-EHP, with the laser excitation threshold at which optical amplification occurs in 2D-EHP by two orders of magnitude lower than in 3D-EHP, and the corresponding value of the coefficient of optical amplification is 2.5 times greater. A simple theoretical model of electron heating in a system with two valleys is applied to describe 2D semiconductor monolayers of the MoS2 and WS2 types. The model is demonstrated to describe sufficiently well the available experimental data on the negative differential conductance effect in a WS2 monolayer. It confirms the possibility to fabricate Gunn diodes of a new and advanced EMW generation based on the structures concerned. These diodes are capable to generate frequencies of the order of 10 GHz and higher, which makes them attractive for HF practical applications. [ABSTRACT FROM AUTHOR]

Nowadays, graded semiconductors attract developers' interest as prospective material which can improve the interaction of the electric field and the electrons in the devices operating on the intervalley electron transfer effect. This effect increases the efficiency and power output of the generation of current oscillations in Gunn diodes. To obtain the best effect graded semiconductor must be optimal by the dependence of the energy gap between the nonequivalent valleys of the conduction band on the coordinate. This paper deals with the results of the investigation of Gunn diodes operation based on graded InGaP-InPAs by means of the temperature model of intervalley electron transfer in graded semiconductors. The paper presents the results of the numerical experiments on efficient generation of electromagnetic waves in the range from 18 to 80 GHz using graded InxGa1-xP-InPyAs1-y Gunn diodes with the active region length of 2.5 μm and concentration of ionized impurities therein of 1016 cm-3. Our findings are the dependences generation efficiency and output power on frequency for different distributions of GaP and InAs in Inx1-xPInPyAs1-y. We have compared obtained results with similar AlxGa1-xAs-GaAs-Ga1-yInyAs-diodes. The maximal obtained power in InxGa1-xP-InPyAs1-y-diode is 11.3 kW·cm-2 at a frequency of 40 GHz with an efficiency of 10.2 % at x = 0.6 and y = 0.6. [ABSTRACT FROM AUTHOR]

Abstract: The planar Gunn diode offers the potential of microwave, milli‐metric and THz‐based oscillators, which can be fabricated as part of a microwave monolithic integrated circuit (mmic). The paper develops an electrical representation of an aluminum gallium arsenide (AlGaAs) based planar Gunn diode with an active channel length of approximately 4 μm and width of 120 μm, embedded in an oscillator circuit. The work indicates a maximum simulated RF output power of +5 dBm compared with published experimental results of −19 dBm for similar diodes. [ABSTRACT FROM AUTHOR]

Coherent summation was performed for the wave fields of pairs of X-band nanosecond Gunn oscillators based on 3A762 diodes. Each oscillator was excited by its own modulator. The initial phase of the microwave pulse of each oscillator was fixed by the leading edge of the electrical pulse from the respective modulator. The modulators were triggered by a common sync pulse. The total microwave-radiation patterns of antenna pairs connected to the Gunn oscillators were in good agreement with the total radiation patterns of these antennas excited in phase by a standard oscillator. [ABSTRACT FROM AUTHOR]

The frequency of a Gunn diode is usually determined by the length of its oscillation channel, hard to be change after the device has been fabricated. We show that in a top-gated planar nanodevice the frequency of Gunn oscillations can be conveniently increased, i.e. tuned by the top-gate bias. Ensemble Monte Carlo (EMC) simulations indicate that the achieved maximum frequency reaches 1 THz, about three times of that of an un-gated device. Moreover, the tunable frequency-range also increases with the length of the top-gate, resulting in a widest range of ∼0.7 THz. Detailed analysis of the Gunn-domain dynamics shows that this tunable effect is related to the simultaneous formation of multi-domains, which are excited by the top-gate induced non-uniformed electricfield along the oscillation channel. [ABSTRACT FROM AUTHOR]

The results of research into the autodyne effect of a self-oscillating system subjected to reflected self-radiation and composed of two mutually synchronized partial oscillators with delayed interconnection are presented. The behavioral peculiarities of autodyne changes in the oscillation amplitude of partial oscillators, frequency, phase difference, and the response in the power supply circuit of active components are discussed at different oscillator parameters and various conditions of their mutual coupling. Experimental data are obtained for the flange-type double-diode oscillator built around 8-mm-band Gunn diodes. [ABSTRACT FROM AUTHOR]

Research results of signal formation features of the autodyne sensor (AS) with sinusoidal frequency modulation (FM) are presented. Expressions for low frequency information signals are given and their numerical analysis is performed for cases when signal period is substantially longer than reflected radiation delay time as well as for the case when this inequality is not fulfilled. It is proved that at a small distance to the reflected object when feedback parameter value is commensurable with 1, the distortions of FM AS signals are typically caused by reflected radiation phase incursion irregularities. When distance grows the distortion level becomes significantly smaller due to delay phenomenon of reflected radiation. Experimental research results are obtained on the example of the autodyne oscillator based on the 8-mm wavelength range Gunn diode with varicap-based FM. [ABSTRACT FROM AUTHOR]

GaN provides the highest electron saturation velocity, breakdown voltage, operation temperature, and thus the highest combined frequency-power performance among commonly used semiconductors. The industrial need for compact, economical, high-resolution, and high-power terahertz (THz) imaging and spectroscopy systems are promoting the utilization of GaN for implementing the next generation of THz systems. As it is reviewed, the mentioned characteristics of GaN together with its capabilities of providing high two-dimensional election densities and large longitudinal optical phonon of ∼90 meV make it one of the most promising semiconductor materials for the future of the THz emitters, detectors, mixers, and frequency multiplicators. GaN-based devices have shown capabilities of operation in the upper THz frequency band of 5 to 12 THz with relatively high photon densities in room temperature. As a result, THz imaging and spectroscopy systems with high resolution and deep depth of penetration can be realized through utilizing GaN-based devices. A comprehensive review of the history and the state of the art of GaN-based electronic devices, including plasma heterostructure field-effect transistors, negative differential resistances, hetero-dimensional Schottky diodes, impact avalanche transit times, quantum-cascade lasers, high electron mobility transistors, Gunn diodes, and tera field-effect transistors together with their impact on the future of THz imaging and spectroscopy systems is provided [ABSTRACT FROM AUTHOR]

The effects of highly out-of-band electromagnetic interference (EMI) on a RF front-end are experimentally evaluated. Signal at 60 GHz with a moderate power is produced in the near-field owing to an open-ended WR15 waveguide fed by a Gunn diode. Due to the nonlinear behavior of active devices, we observed a gain quenching leading to complete extinction of either the transmitter or the receiver of the front-end subject to EMI. The paper proposes a detailed analysis of both CW and chopped EMI by varying almost all experimental conditions, namely the polarization, the target distance, and the chopping mode. [ABSTRACT FROM AUTHOR]

The effects of highly out-of-band electromagnetic interference (EMI) on an RF front-end are experimentally evaluated. Irradiation at 60GHz with a moderate power is produced in the near-field owing to an open-endedWR15 waveguide fed by a Gunn diode. Surprisingly, we easily obtain the remote extinction of either the transmitter or the receiver of the front-end subject to EMI. The paper proposes a detailed analysis of both CW and chopped EMI by varying almost all experimental conditions, namely the polarization, target distance, and chopping mode. The latter shows most efficiency and evidences some long time scale dynamics in the induced perturbation. [ABSTRACT FROM AUTHOR]

Current oscillations in an AlGaAs/InGaAs/AlGaAs-based two-dimensional electron gas (2DEG)-based hetero-structure have been investigated by means of semiconductor device simulation software SILVACO, with an interest on the charge domain formation at large biases. Single-frequency oscillations are generated in planar Gunn diodes with uniform anode and cathode contacts. The oscillation frequency reduces as the applied bias voltage increases. We show that it is possible to create multiple, independent charge domains in a novel Gunn diode structure with designed multiple anode-cathode spacings. This enables simultaneous generation of multiple frequency oscillations in a single planar device, in contrast to traditional vertical Gunn diodes where only single-frequency oscillations can be achieved. More interestingly, frequency mixing in multiple-channel configured Gunn diodes appeared. This proof-of-concept opens up the possibility for realizing compact self-oscillating mixer at millimeter-wave applications. [ABSTRACT FROM AUTHOR]

Microwave-signal generation in planar Gunn diodes with a two-dimensional electron gas, in which we previously studied steady-state electron transport, is theoretically studied. The applicability of a control electrode similar to a field-effect transistor gate to control the parameters of the output diode microwave signal is considered. The results of physical-topological modeling of semiconductor structures with different diode active-region structures, i.e., without a quantum well, with one and two quantum wells separated by a potential barrier, are compared. The calculated results are compared with our previous experimental data on recording Gunn generation in a Schottky-gate field-effect transistor. It is theoretically and experimentally shown that the power of the signal generated by the planar Gunn diode with a quantum well and a control electrode is sufficient to implement monolithic integrated circuits of different functionalities. It is theoretically and experimentally shown that the use of a control electrode on account of the introduction of corrective feedback allows a significant increase in the radiation resistance of a microwave generator with Schottky-gate field-effect transistors. [ABSTRACT FROM AUTHOR]

A numerical study for an AlGaAs/InGaAs-based quantum well structure planar Gunn diodes was performed by initially proposing imperfect metallic contacts that can introduce multiple anode–cathode spacings caused by etching process during the fabrication. Through Fast Fourier transform (FFT) algorithm, the result reveals that, at moderate bias voltage above the threshold, multi-channel planar Gunn diode exhibits multiple oscillations which were consistent with experimental observation due to non-uniformity of contact terminal. A downwards shift of oscillation frequency by varying the applied voltage across terminal was observed due to Gunn effect. The finding may be utilized not only to generate multiple millimeter wave or even terahertz signal sources on single chip, but also to achieve frequency tunability through tuning the applied bias voltage. [ABSTRACT FROM AUTHOR]

The expressions describing the autodyne (AD) response are obtained with allowance for the internal noise of a frequency-stabilized microwave oscillator subjected to the action of its self-radiation reflected from an object. The results of analyzing the AD and noise characteristics of the stabilized oscillator built around the band-reflecting filter with resistive coupling are presented. The conditions leading to the appearance of the periodic non-stationarity of noise characteristics are established. It is demonstrated that frequency stabilization is ensured by a gain in dynamic range. The experimental data on unstabilized and stabilized hybrid-integral AD oscillators based on the two-mesa Gunn diode of 8-mm range are presented. [ABSTRACT FROM AUTHOR]

We present an explicit numerical analysis on GaN-based multi-quantum-well planar Gunn diodes. The simulation demonstrates that Gunn oscillations generated in the multi-channel can be self-synchronized to each other, which significantly improves the output characteristics of planar Gunn diode due to the superposition of the dipole domain in each channel. The optimized output characteristics are obtained in the triple-channel Gunn diode, where the RF output power is about 6.45 mW and the DC-to-RF conversion efficiency is about 2.39% at the fundamental frequency of 216.05 GHz, more than three times larger than that of the single-channel AlGaN/GaN Gunn diode. The proposed GaN HEMT-like multi-channel planar Gunn diode with higher level of output characteristics shows great potential as a solid-state radiation source of millimeter-wave and sub-terahertz. [ABSTRACT FROM AUTHOR]

The radiation resistance of planar Gunn diodes is investigated. Based on the results of measurements of the pulsed current-voltage characteristics and computer simulations it is shown that the use of δ layers of doping impurities contributes to the higher radiation resistance of planar diodes by an order of magnitude compared to conventional Gunn diodes. The results of this study make it possible to formulate methodical guidelines to reduce the amount of computational and experimental studies without a considerable decrease in their informativity. [ABSTRACT FROM AUTHOR]

Experimental data on manufacturing the ohmic contacts Au-Ti-Pd-n+-InP, formed using vacuum deposition of metal onto a heated to 300 °C substrate representing an epitaxial n+-n-n++-n+++-InP structure. The specific contact resistance measured at room temperature was about 7·10-5 Ohm·cm². Voltage-current characteristics within the temperature range 110 to 380 K are linear. Gunn diodes with such contacts, which were made as a straight mesa-structure in a pulsed mode (pulse duration of 100 ns, pulse ratio of 1000, operating current of 2.2 A), generated the microwave power ~10 mW in the V-band. [ABSTRACT FROM AUTHOR]

The current capability and frequency of InGaAs-based planar Gunn diode have been studied using numerical simulation. Our simulated results are well in agreement with the experimental observation with fundamental frequency operating up to 116 GHz. Through the Fast Fourier transform algorithm, it has been revealed that oscillating frequency tunes downward slightly with increased applied voltage above threshold voltage, and a second-harmonic frequency is observed at 233 GHz for 1.45-μm channel length. This structure provides feasibility of generating a tunable millimeter wave or terahertz wave source and has an overwhelming advantage over equivalent traditional vertical structure because of increased facilitated integration and flexibility. [ABSTRACT FROM AUTHOR]

The principle of operation and design of an 8-mm autodyne transceiver module, based on two mutually synchronized Gunn diode oscillators, and schemes of the signal detection unit in the Gunn-diode supply circuit are described. The oscillation frequency of the autodyne is stabilized by an additional high-Q resonator, connected to the working resonator using a reflection circuit with resistive coupling. The measured data on the double-diode autodyne oscillator are presented and recommendations on its tuning are given. It is shown that the presence of quadrature signals and high stability of the oscillation frequency of the double-diode autodynes ensure some new possibilities, when they are used to solve problems of near-field radio location, checking product sizes, and measuring vibration and displacement parameters. [ABSTRACT FROM AUTHOR]

This letter describes the use of a novel micro-particle sensor ( \sim 3\mu \textm diameter) and infra-red microscopy to measure the temperature profile within the active channel (typically 3- \mu \textm length and 120- \mu \textm width) of planar Gunn diodes. The method has enabled detailed temperature measurements showing an asymmetrical temperature profile along the active width of these devices. The asymmetrical temperature profile suggests a similar behavior in the channel current density, which may contribute to the lower than expected RF output power. [ABSTRACT FROM AUTHOR]

The 'intrusion' of the phase of a Gunn-diode nanosecond microwave oscillator by applying a modulating voltage pulse is numerically simulated. The dependences of the microwave oscillation phase on the spread of the pulse rise time and modulating pulse amplitude are revealed. The standard deviation of the phase lag time in a 3-cm-range oscillator relative to a fixed level at the leading edge of the modulating phase is measured. Phase synchronization between two electrodynamically uncoupled oscillators that are simultaneously excited by a single modulator is studied experimentally. [ABSTRACT FROM AUTHOR]

We develop time-domain simulations of microwave and THz radiation sources built as arrays of active devices when the radiation wavelength is small as compared to spacing between electronic components. We pursue an approach when the system is represented by equations with time-delay feedback that could generate chaos and other forms of complicated dynamics. The approach simplifies simulations of ultra-wideband effects and exceeds capabilities of frequency-domain methods. As a model case, we simulated a microstrip circuit with Gunn diode and a remote resonator emitting the radiation towards infinity. We observed the emergence of either the continuous waves or the trains of high-frequency pulses depending on the bias conditions. We found bistability and hysteresis in the onset of different oscillation modes that depends on the way of driving the bias voltage into the domain of instability of the given system. The results would allow one to improve the design of THz radiation sources with time-delay coupling between components. [ABSTRACT FROM AUTHOR]

This work presents two different approaches for the implementation of pseudomorphic high electron mobility transistors (pHEMTs) and planar Gunn diodes on the same gallium arsenide substrate. In the first approach, a combined wafer is used where a buffer layer separates the active layers of the two devices. A second approach was also examined using a single wafer where the AlGaAs/InGaAs/GaAs heterostructures were designed for the realisation of pHEMTs. The comparison between the two techniques showed that the devices fabricated on the single pHEMT wafer presented superior performance over the combined wafer technique. The DC and small-signal characteristics of the pHEMTs on the single wafer were enhanced after the use of T-gates with 70 nm length. The maximum transconductance of the transistors was equal to 780 mS/mm with 200 GHz maximum frequency of oscillation ( f max ). Planar Gunn diodes fabricated in the pHEMT wafer, with 1.3 μm anode-to-cathode separation ( L AC ) presented oscillations at 87.6 GHz with maximum power of oscillation equal to −40 dBm. [ABSTRACT FROM AUTHOR]

ABSTRACT This letter reports the highest fundamental oscillator operating frequency of 120 GHz for gallium arsenide (GaAs)-based Gunn diode. The letter describes the design, fabrication, and test of the aluminum gallium arsenide (AlGaAs)/(GaAs) planar Gunn diode with an anode to cathode separation of 1 μm and channel width of 120 μm. The planar Gunn diode was designed with an integrated series inductor in coplanar waveguide format. The experimental results showed that the planar Gunn diode oscillated at a fundamental frequency of 120.47 GHz with an RF output power −9.14 dBm. This is highest fundamental frequency and power recorded for a GaAs-based Gunn diode. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2449-2451, 2014 [ABSTRACT FROM AUTHOR]

We present the cofabrication of planar Gunn diodes and high-electron mobility transistors (HEMTs) on an indium phosphide substrate for the first time. Electron beam lithography has been used extensively for the complete fabrication procedure and a 70-nm T-gate technology was incorporated for the enhancement of the small-signal characteristics of the HEMT. Diodes with anode-to-cathode separation ( \(L_{\rm ac}\) ) down to 1- and 120- \(\mu \) m width were shown to oscillate up to 204 GHz. The transistor presents a cutoff frequency ( \(f_{_{T}}\) ) of 220 GHz, with power gain up to 330 GHz ( \(f_{\max }\) ). The integration of the two devices creates the potential for the realization of high-power, high-frequency MMIC Gunn oscillators, circuits, and systems. [ABSTRACT FROM AUTHOR]

ABSTRACT A two-diode injection locked power combiner has been designed with computer-aided design approach and experimentally tested. An output power of 25.48 dBm with a phase noise of −100 dBc/Hz for a frequency offset of 10 kHz from the carrier frequency of 34.6 GHz has been achieved. The power-combiner cavity has been simulated with 3D full wave electromagnetic field simulator HFSS and cosimulated with the equivalent circuit of the continuous wave Gunn diode using ANSYS Designer. The experimental result closely matches with the simulation and is better than the analytical approach reported by earlier researchers. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:705-709, 2014 [ABSTRACT FROM AUTHOR]

In this work, recent advances in the design of GaN planar Gunn diodes with asymmetric shape, socalled self-switching diodes, are presented. A particular geometry for the nanodiode is proposed, referred as V-shape, where the width of the channel is intentionally increased as approaching the anode. This design, which reduces the effect of the surface-charges at the anode side, is the most favourable one for the onset of Gunn oscillations, which emerge at lower current levels and with lower threshold voltages as compared to the standard square geometry, thus enhancing the power efficiency of the self-switching diode as sub-millimeter wave emitters. [ABSTRACT FROM AUTHOR]

Scanning confocal micro-Raman and PL spectroscopy, Kelvin probe force microscopy (KPFM) and electrostatic force gradient microscopy (EFGM) were applied to study the concentration profiles of free carriers by scanning the cleaved edge along the growth direction of vertical n+/n0/n+-GaN Gunn-diode structure. The vertical frequency profile of the L- branch of the plasmon-LO-phonon modes was used to evaluate the concentration of free charge carriers. Obtained significant contrast through the undoped n0-GaN region validates the expected reduction in carrier concentration. Variation of the local contrast in cross-section KPFM and EFGM electrical images reflects the topology of the device structure and makes it possible to estimate electronic properties of individual GaN layers as well as interface boundaries. The carrier profiles determined from the Raman data and KPFM measurements are in good agreement. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The results of local contactless measurement of the dependence of conductivity in a Gunn diode on the external electrical bias are presented. The technique of local determination of the charge-carrier concentration and mobility in a commercially produced chip Gunn diode for various values of the supply voltage is proposed. [ABSTRACT FROM AUTHOR]

Mesa etching technology is considerably important in the Gunn diode fabrication process. In this paper we fabricate InP Gunn diodes with two different kinds of chlorine-based etchants for the mesa etching for comparative study. We use two chlorine-based etchants, one is HCl-based solution (HCl/H3PO4), and the other is Cl2-based gas mixture by utilizing inductively coupled plasma system (ICP). The results show that the wet etching (HCl-based) offers low cost and approximately vertical sidewall, whilst ICP system (Cl2-based) offers an excellent and uniform vertical sidewall, and the over-etching is tiny on the top and the bottom of mesa. And the fabricated mesas of Gunn diodes have average etching rates of ∼ 0.6 μm/min and ∼ 1.2 μm/min, respectively. The measured data show that the current of Gunn diode by wet etching is lower than that by ICP, and the former has a higher threshold voltage. It provides a low-cost and reliable method which is potentially applied to the fabrication of chip terahertz sources. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) measurement is used to study the point defect distribution in a GaN terahertz Gunn diode, which is able to the degrade high-field transport characteristic during further device operation. PL, secondary ion mass spectroscopy (SIMS), transmission electron microscope (TEM), and capacitance—voltage (C—V) measurements are used to discuss the origin of point defects responsible for the yellow luminescence in structures. The point defect densities of about 1011 cm−2 in structures are extracted by analysis of C—V characterization. After thermal annealing treatment, diminishments of point defect densities in structures are efficiently demonstrated by PL and C—V results. [ABSTRACT FROM AUTHOR]

Terahertz oscillations of AlGaN/GaN HEMT-like planar Gunn diodes with the channel length ranging from 0.6 to 1.6 μm have been investigated for the first time by means of numerical simulations at the Silvaco's ATLAS platform, with an emphasis on the mechanism of multiple domains coexisting in the 2-D electron gas (2-DEG) channel of planar Gunn diode. We found that the phenomenon of multidomain evidently influences the oscillation mode and the radio frequency performance of devices, and it is effective in redistributing the electric field throughout the 2-DEG channel by adjusting the doping concentration near the cathode side, which aims to modulate the formation of multidomain so as to enhance the output performance of planar Gunn diodes at terahertz frequencies. [ABSTRACT FROM AUTHOR]

A near-field microwave microscope based on a semiconductor Gunn-diode autodyne oscillator with a probe fabricated using a microcoaxial-waveguide junction with a microcoaxial section whose central conductor extends beyond its outer conductor. The possibility of high-spatial-resolution visualization of the relief and electrical properties of the surface of a ceramic plate with a deposited nanometer-scale metal layer is demonstrated using the autodyne near-field microwave microscope in the mode of direct access to the object to be scanned and in the mode of subsurface probing. [ABSTRACT FROM AUTHOR]

Non-linearity is observed in the transfer characteristics of gunn diode. Neural Network can elegantly solve a typical regression of characteristic of gunn diode. The dataset is obtained by performing experiment on a typical continuous wave gunn diode MA49156-30. The numbers of readings are regarded as samples. The dataset is obtained, which is used for regression. After rigorous computer simulations authors develop an optimal MLP NN model, which elegantly performs such a nonlinear regression. Results show that the proposed optimal MLP NN model has a MSE as low as 4.24 x 10-5, correlation coefficient as high as 0.9852 when it is validated on the cross validation dataset. [ABSTRACT FROM AUTHOR]

The paper deals with the numerical simulation of Gunn diodes operation based on the graded-gap AlInN. We have obtained the output characteristics of diodes with different cathode contacts in a wide range of frequencies. Harmonic and biharmonic modes of operation have been considered. Cutoff frequency and minimum length of the active region have been estimated. Performances of graded-gap AlInN diodes are compared with the performances of InN and AlN diodes. [ABSTRACT FROM AUTHOR]

The results of an investigation of the thermal resistance of Gunn diodes at different process technology cycles of their manufacturing are considered. [ABSTRACT FROM AUTHOR]