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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.

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]

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]

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]

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]

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]

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]

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]

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]

Impact ionization in GaAs-based planar Gunn diodes is studied through electroluminescence (EL) analysis with the aim of reducing its magnitude by means of contact design and shaping, and thus enhance device performance and reliability. Designs in which the diode ohmic anode has an overhanging Schottky extension (composite anode contact) are shown to result in a significantly reduced amount of impact ionization, as compared with a simple ohmic contact design. The EL results are consistent with Monte Carlo simulations, which show a reduced impact ionization in composite anode contact devices due to a reduced electron density beneath the anode Schottky extension that, on the one hand, weakens the Gunn domain electric field and softens its variations near the anode edge, and, on the other hand, reduces the number of electrons capable of generating holes by impact ionization. A comparison between standard and composite anode contact approaches in terms of radio-frequency operation of the devices is made showing oscillations up to 109 GHz with an output power of -5 dBm in devices featuring the composite anode contact and no oscillations from all-ohmic contact devices. The findings reported in this paper may be useful not only for the design and the fabrication of planar Gunn diodes but also for other devices such as high-electron-mobility transistors where impact ionization can result in reliability limitations. [ABSTRACT FROM AUTHOR]

This paper presents an improved negative differential mobility model for GaN and AlGaN to simulate GaN Gunn diodes at terahertz frequencies. Temperature-dependent parameters \nusat, Ec, \alpha, \delta, and \gamma are proposed to improve the accuracy of the mobility model at high temperatures. In particular, an Al-composition-related coefficient fZ(x) and a random-alloy-potential-related factor falloy(p) are developed for an AlGaN mobility model. Simulation results show that notched doping GaN and AlGaN/GaN heterostructure Gunn diodes, both including 0.6-\mu\m transit and 0.2-\mu\m electron launching regions, have the capability of generating fundamental frequencies of 352–508 and 332–469 GHz, respectively, with a maximum radio-frequency (RF) power density of \sim \10^10\ \W/cm^3 and RF efficiency of over 2% accompanied with a shift of an oscillation mode from a dipole-domain mode toward an accumulation mode as the temperature rises from 300 to 500 K. [ABSTRACT FROM AUTHOR]

A drastic reduction in the residual voltage (from ~100 V to a few volts) and a significant (factor of ~2) increase in the dU / dt switching rate is demonstrated experimentally in the superfast (~200 ps) avalanche switching of a GaAs bipolar junction transistor with increased emitter area. This result is not a trivial one as only a small number of conductive channels of a few micrometers in diameter participate in the transient independently of the emitter size, while the remaining (passive) part of the structure supplies the switching channels with the currents circulating inside the chip, which makes the impact ionization in the filaments even more powerful. Excellent agreement was found between the experiment and a "two-transistor" model specially developed here, with one transistor simulating the switching channels and the other the nonswitched part of the structure. Much higher switching stability and reproducibility and much lower power dissipation were observed in the structure with increased emitter area. [ABSTRACT FROM AUTHOR]

In this paper, we report on the bias oscillation of GaN-based Gunn diodes realized on a n+-GaN substrate. Different contact materials, ambient gases, and pulsewidths were used and compared with regard to device stability. A wide negative-differential-resistance (NDR) region was measured for electrical-field values E larger than a threshold field Eth of 150 kV/cm. Electrical fields much higher than the threshold value did not lead to any electromigration effects or discharging problems from the contacts. The drift velocity derived from the current-voltage characteristics, diode geometry, and doping concentration in the active layer was estimated to be 1.9 x 107 cm/s. Bias oscillations were obtained for the GaN Gunn diodes in the presence of a series inductance. [ABSTRACT FROM AUTHOR]

Design of tunable Gunn diode-based active antenna module including a new type of planar dielectric resonator (PDR) tuned by a ferroelectric (FE) varactor is presented. The module is designed in such a way that the PDR acts both as a stabilizing resonator and as a radiator. Microwave properties of FE elements used for voltage-controlled oscillator (VCO) tuning are considered. The module operates at a frequency around of 17 GHz and demonstrates the radiated power of 8.8±0.1 dBm over the 130-MHz tuning range and a phase-noise level of -80 dBcIHz at 100-kHz offset. 65° width of the radiation pattern in both the E- and H-planes corresponding to a gain of 5.1 dBi was measured. The VCO module has been tested in the regime of the frequency modulation. The output signal spectra measured and simulated for modulating bipolar voltage pulses of repetition frequency f = 2MHz are presented. [ABSTRACT FROM AUTHOR]

The n+-n-n+-n++-GaAs epitaxial structures were MBE-grown on porous nanostructured and traditional (standard) heavily doped n++-GaAs substrates. On their basis, we fabricated the Gunn diodes generating power output in the 44—59 GHz (first harmonic) and 101—104 GHz (second harmonic) frequency ranges. For both harmonics, the power output of the Gunn diodes grown on porous substrates was shown to be from 20 to 30% higher than those grown on the flat ones. [ABSTRACT FROM AUTHOR]

A low-cost, high-performance X-band Gunn diode oscillator for educational and research purposes has been developed. The cavities have been manufactured on a standard WR90 rectangular waveguide with UBR100 flange in order to make it compatible with the waveguide circuitry usually available in a basic microwave laboratory. The capability of sweeping the whole X band at constant output power and low phase noise, as well as the low cost of its components, make this device suitable for users at any level. As an example of its many educational applications, a multiple frequency continuous-wave (MFCW) radar has been developed, and the results of the laboratory implementation are shown. [ABSTRACT FROM AUTHOR]

Examines the W-band overmoded-waveguide oscillator with Gunn diodes. Output power and efficiency of gunn diodes contained in the waveguide array; Improvement on the efficiency of the gunn diodes using a small resonator; Conversion on the output mode of fundamental-mode waveguides.

Discusses the improved heat dissipation of InP Gunn devices. Radio frequency power levels and oscillation frequencies resulting from the improved heat dissipation; Corresponding direct current-to-radio frequency conversion efficiencies; Properties of millimeter-wave devices.

Focuses on the development of a millimeter-wave oscillator which incorporates an overmoded-waveguide resonator with an array of fundamental-mode waveguides containing Gunn Diodes. Use of mode conversion of radiation power from Gunn diodes in the waveguide array; Configuration of an overmoded-waveguide oscillator with diode devices.

Presents a cavity-backed, Gunn-diode-driven, self-mixing active inverted stripline circular patch antenna. Active antenna configuration; Evaluation of the performance of the active antenna; Evaluation of the varactor-tuning capabilities of the device.