Gunn Diode Research Articles

Characteristics of a GaN-based Gunn diode for THz signal generation

A generalized large-signal computer simulation program for a Gunn oscillator has been developed. The properties of a Gunn diode oscillator based on the widely explored GaN, are investigated using the developed program. The results show some interesting properties in GaN Gunn diodes which are not seen in GaAs and InP diodes. An output power of 1400 kW/cm2 is achieved from the GaN Gunn diode, as compared to 4.9 kW/cm2 from a GaAs diode.

Nonresonant Detection of Terahertz Radiation in High-Electron-Mobility Transistor Structure Using InAlAs/InGaAs/InP Material Systems at Room Temperature

In this paper, we report on nonresonant detection of terahertz radiation using the rectification mechanism of two-dimensional plasmons in high-electron-mobility transistors using InAIAs/InGaAs/InP material systems. The experiments were performed at room temperature using a Gunn diode operating at 0.30 THz as the THz source. The measured response was dependent on the polarization of the incident THz wave; The device exhibited higher response when the electric-field vector of the incident radiation was directed in the source-drain direction. The 2D spatial distribution image of the transistor responsivity extracted from the measured response shows a clear beam focus centered on the transistor position, which ensures the appropriate coupling of the terahertz radiation to the device. The device also demonstrated excellent sensitivity/noise performances of approximately 125 V/W and approximately 10(-11) W/Hz(0.5) under 0.30 THz radiation.

Analysis of Gunn Loaded Rectangular Microstrip Antenna

Analysis on rectangular microstrip antenna with Gunn loaded on it using equivalent circuit concept reveals that the bandwidth is increased to 10.43% over the 2.9% of patch alone. It is observed that the rectangular microstrip antenna loaded with Gunn diode offers wider tunability (9.308 GHz-9.161GHz) for bias voltage from 8–15V for a given threshold voltage of 4.4V. The radiated power is enhanced by 0.15dB as compared to patch alone.

Searching for THz Gunn oscillations in GaN planar nanodiodes

A detailed study of GaN-based planar asymmetric nanodiodes, promising devices for the fabrication of room temperature THz Gunn oscillators, is reported. By using Monte Carlo simulations, an analysis of the static I-V curves and the time-domain evolution of the current obtained when varying some simulation parameters in the diodes has been made. Oscillation frequencies of hundreds of GHz are predicted by the simulations in diodes with micrometric channel lengths. Following simulation guidelines, a first batch of diodes was fabricated. It was found that surface charge depletion effects are stronger than expected and inhibit the onset of the oscillations. Indeed, a simple standard constant surface charge model is not able to reproduce experimental measurements and a self-consistent model must be included in the simulations. Using a self-consistent model, it was found that to achieve oscillations, wider channels and improved geometries are necessary.

우수한 성능의 94 GHz 도파관 전압조정발진기의 개발

In this paper, we developed a 94 GHz waveguide VCO(voltage controlled oscillator) using a GaAs-based Gunn diode and a varactor diode. The cavity is designed for fundamental mode at 47 GHz and operated at second harmonic of 94 GHz. Bias posts for diodes operate as LPF(low pass filter) and resonator. The fabricated waveguide VCO achieves an oscillation bandwidth of 760 MHz. Output power is from 12.61 to 15.26 dBm and phase noise is -101.13 dBc/Hz at 1 MHz offset frequency from the carrier.

A comparative investigation on sub-micrometer InN and GaN Gunn diodes working at terahertz frequency

We report on a simulation for wurtzite-InN and GaN Gunn diodes with notch-doping and uniform-doping structural transit regions. Results show that 0.3–1.0 μm Gunn diodes with a diode area of 500 μm2 can generate fundamental frequencies of around 0.2–0.8 THz and rf currents of several hundred mA. InN diodes exhibit more stable oscillations, whereas GaN diodes generate higher oscillation frequencies at both dipole-domain mode and accumulation-domain mode due to different negative differential resistance (NDR) characteristics of high-field transport. The sharp NDR region of InN makes it more suitable for short transit region Gunn diode. Higher Irf/Iav and lower bias voltage in InN Gunn diode imply its conversion efficiency significantly higher than GaN diode.

GaN based transfer electron and avalanche transit time devices

A new model is developed to study the microwave/mm wave characteristics of two-terminal GaN-based transfer electron devices (TEDs), namely a Gunn diode and an impact avalanche transit time (IMPATT) device. Microwave characteristics such as device efficiency and the microwave power generated are computed and compared at D-band (140 GHz center frequency) to see the potentiality of each device under the same operating conditions. It is seen that GaN-based IMPATT devices surpass the Gunn diode in the said frequency region.

FMCW 응용을 위한 우수한 성능의 W-band 도파관 전압조정발진기

In this paper, we reported on a high performance waveguide VCO(voltage controlled oscillator) for FMCW applications. The waveguide VCO consists of a GaAs Gunn diode, a varactor diode, and two bias posts with low pass filter(LPF). The cavity is designed for fundamental mode at 47 GHz and operated at second harmonic of 94 GHz center frequency. The developed waveguide VCO has 1.095 GHz bandwidth, 590 MHz linearity with 1.69% and output power from 14.86 to 15.93 dBm. The phase noise is under -95 dBc/Hz at 1 MHz offset.

Nondestructive testing of the thermal resistance of Gann diodes during their manufacture

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

Reduction of Impact Ionization in GaAs-Based Planar Gunn Diodes by Anode Contact Design

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.

Three-Terminal Graphene Negative Differential Resistance Devices

A new mechanism for negative differential resistance (NDR) is discovered in three-terminal graphene devices based on a field-effect transistor configuration. This NDR effect is a universal phenomenon for graphene and is demonstrated in devices fabricated with different types of graphene materials and gate dielectrics. Operation of conventional NDR devices is usually based on quantum tunneling or intervalley carrier transfer, whereas the NDR behavior observed here is unique to the ambipolar behavior of zero-bandgap graphene and is associated with the competition between electron and hole conduction as the drain bias increases. These three terminal graphene NDR devices offer more operation flexibility than conventional two-terminal devices based on tunnel diodes, Gunn diodes, or molecular devices, and open up new opportunities for graphene in microwave to terahertz applications.

Intense superminiature beamless generators in gas-discharge microwave electronics

Intense microwave generators intended for mass production are characterized by a number of parame� ters, the mass, size, and cost always being the most important among them. The lighter and more inex� pensive a microwave generator, the more attractive it seems to be for potential employment. When we deal with very intense (>1 MW) and superintense (>1 GW) microwave generators, we usually relate them to either electronic devices, such as travelingwave tubes (TWTs), backwardwave tubes (BWTs), klystrons, magnetrons, gyrotrons, virtual cathode oscillators, etc., or plasma devices, e.g., plasmabeam generators. In all of them, the energy of highcurrent electron beams is transformed to micro� waveradiation energy. The necessity to apply electron beams imposes sig� nificant constraints on the exterior characteristics of these generators, in particular, on their mass, size, and cost. For example, in addition to basic systems such as electrodynamic structures and antennas, these gener� ators need rather cumbersome auxiliary equipment. Here, we imply a vacuum system producing a deep vacuum (down to ~10 -5 Torr), a highly efficient cath� ode providing highdensity electronemission current (>10 kA cm -2 ), an intense highvoltage powersupply unit (>100 kV) required to accelerate the electron beam, and an electron collector. A magnetic system providing the presence of the magnetic field (>1 kG) within the entire volume of the electrodynamic system is also required. It is necessary to prevent the electron� beam divergence caused by the Coulomb repulsion. As a result, all these auxiliary systems determine ulti� mately the noticeable mass, size, and cost of the microwave generators. In addition to the information given above, the electrodynamic structures, in themselves, of intense electronic microwave generators, as a rule, are charac� terized by a large size. It is convenient to express the volume V of generator electrodynamic structures in terms of the cubic wavelength λ 3 = (c/F) 3 . Here, c is the speed of light in a vacuum and F is the carrying fre� quency of the microwave radiation generated in the structure. Usually, the volume of an intense electronic microwave generator is V > λ 3 , whereas the volume of a superintense multiwave generator is, often, V > (10λ) 3 . For comparison, we may say that in lowinten� sity semiconductor microwave generators (avalanche� flight diodes, Gunn diodes), the volume of the work� ing generation zone is V λ 3 . Thus, we may call these generators miniature devices.

A simple Fourier transform spectrometer for terahertz applications

A simple Fourier transform spectrometer was designed and constructed for the measurement of detectors, sources, passive devices and materials in the terahertz (THz) range. It can be operated at frequencies between 0.3 and 1.5 THz, using a 50-μm-thick Mylar-film beam splitter. The spectral range can be changed by altering the thickness of the beam splitter. The highest frequency resolution is 750 MHz. We studied the properties of heterodyne detectors including superconductor mixers and semiconductor harmonic mixers, direct detectors including an InSb semiconductor bolometer, superconducting tunnel junctions and the Golay cell, and sources including Gunn oscillators and a microwave source with its multipliers, as well as various materials and passive devices including Si wafers and metal mesh filters.

STUDIES ON THE DYNAMICS OF A SYSTEM OF BILATERALLY COUPLED CHAOTIC GUNN OSCILLATORS

The dynamics of a system of two bilaterally coupled chaotically oscillating X-band Gunn oscillators (GOs) has been studied by numerical simulation and by hardware experiment. The efiect of variation of the coupling strengths between two oscillators in two paths has been explored. The chaotic oscillations in two GOs have become synchronized in most of the cases when coupling factors (CFs) are around 20% or more. However, the transformation of chaotic states of the GOs to quasi-periodic ones has been observed for some values of CFs. A detailed numerical analysis on the instantaneous error parameters of the GO state variables is presented to identify difierent steady state dynamical conditions of the system. Experimental observations of the GO output frequency power spectra and the averaged product of the two GO outputs in the coupled mode conflrm the occurrence of synchronization as well as quenching of chaotic oscillations for difierent values of CFs.

SOME NUMERICAL AND EXPERIMENTAL OBSERVATIONS ON THE GROWTH OF OSCILLATIONS IN AN X-BAND GUNN OSCILLATOR

The dynamics of the onset of oscillations in a wave guide cavity based Gunn Oscillator (GO) has been critically examined through numerical simulations and experimental studies. The transition of the GO from a non-oscillatory to an oscillatory state and the same in the reverse direction occurs at different critical values of the dc bias voltage applied to the GO. In presence of a weak RF field in GO cavity, oscillations with broad band continuous spectrum and multiple discrete line spectrum are observed at the GO output for different values of dc bias below the above mentioned critical values. Analysing the numerically obtained time series data, chaos quantifiers have been obtained to prove the occurrence of the chaotic oscillations in the GO. Experimental results and observations of numerical simulation show good qualitative agreement.

ACTIVE SLOT-RING ANTENNAS AS A RECEIVERS

A Gunn mounted active microstrip slot-ring antenna (ASRA) has been investigated for the reception of FM microwave signal. Current well/valley phenomenon has been successfully utilized to demodulate the modulation information. The monolithic behaviour of an active slot-ring antenna as a lock-in amplifler, FM (Frequency Modulation) to AM (Amplitude Modulation) converter and square law detector has been demonstrated in this paper. Theoretical analysis coupled with experimental results has been presented. The proposed receiving scheme is unique in the sense that it does not require IF electronics for the purpose of demodulation. It also works well in a multi-channel environment due to the excellent noise-squelching property of an Injection Locked Gunn Oscillator.

Design of interferometer system on Versatile Experiment Spherical Torus (VEST) at Seoul National University

A 94 GHz heterodyne interferometer system was designed to measure the plasma density of VEST (Versatile Experiment Spherical Torus), which was recently built at Seoul National University. Two 94 GHz Gunn oscillators with a frequency difference of 40 MHz were used in the microwave electronics part of a heterodyne interferometer system. A compact beam focusing system utilizing a pair of plano-convex lenses and a concave mirror was designed to maximize the effective beam reception and spatial resolution. Beam path analysis based on Gaussian optics was used in the design of the beam focusing system. The design of the beam focusing system and the beam path analysis were verified with a couple of experiments that were done within an experimental framework that considered the real dimensions of a vacuum vessel. Optimum distances between the optical components and the beam radii along the beam path obtained from the experiments were in good agreement with the beam path analysis using the Gaussian optics. Both experimentation and numerical calculations confirmed that the designed beam focusing system maximized the spatial resolution of the measurement; moreover, the beam waist was located at the center of the plasma to generate a phase shift more effectively in plasmas. The interferometer system presented in this paper is expected to be used in the measurements of line integrated plasma densities during the start-up phase of VEST.

Design of Half Mode Substrate Integrated Waveguide Gunn Oscillator

Based on the half mode substrate integrated waveguide (HMSIW) technology, a new type of Gunn diode oscillator was developed. Main emphasis was placed on HMSIW resonant cavity structure. Restrictions on the performance of the oscillators imposed by packaged networks and the self-characteristic of the Gunn diode device have been analyzed and then the HMSIW Gunn oscillator design with higher output power is optimized. This oscillator's performance is characterized by an output power of 13.2 dBm, phase noise less than -97.3 dBc/Hz at 100 kHz, output frequency of 26 GHz and frequency excursion of 40 MHz over a temperature range from 10 °C to 75 °C. It has some advantages such as planar integration, low cost, small size, good temperature-frequency stability, and low phase noise.

The impact of resonator detuning on autodyne characteristics of stabilized microwave generators

Results of investigations of autodyne characteristics of microwave generators stabilized by an external high-Q resonator as a function of the oscillations frequency detuning and the natural frequency of the stabilizing resonator have been presented. Main mathematical expressions describing the autodyne response of generator to the impact of intrinsic radiation reflected from target were obtained. The design of the coupling between the main working and stabilizing resonators was implemented by using a circuit of band-reflecting filter with resistive coupling. The calculations of amplitude, frequency, and amplitude-frequency characteristics of the autodyne system were carried out under various conditions. The experimental data qualitatively corroborating the inferences of theoretical studies were obtained by investigating the case of a hybrid-integral 8-mm band Gunn oscillator.

Investigation of Loading Effect on Power Performance for Planar Gunn Diodes Using Load-Pull Measurement Technique

A one-port load-pull measurement has been carried out in order to investigate the effect of loading on the RF power performance of a planar Gunn diode operating in the transit-time mode at 102 GHz. A W-band manual E-H tuner was applied between a waveguide mixer and a wafer probe to vary the load impedance on the Gunn diode. It has been found that more than 25 dB variation of output power was obtained by systematically adjusting the tuner. By de-embedding the S-parameters of the probe, E-H tuner and mixer, the relationship between RF power and load impedance for the planar Gunn diode was derived. This method is extremely useful for assisting the design of matching networks to improve power output of one-port oscillator devices.