Gunn Diode Research Articles

Gunn-Hilsum Effect in Mechanically Strained Silicon Nanowires: Tunable Negative Differential Resistance

Gunn (or Gunn-Hilsum) Effect and its associated negative differential resistivity (NDR) emanates from transfer of electrons between two different energy subbands. This effect was observed in semiconductors like GaAs which has a direct bandgap of very low effective mass and an indirect subband of high effective mass which lies ~300 meV above the former. In contrast to GaAs, bulk silicon has a very high energy spacing (~1 eV) which renders the initiation of transfer-induced NDR unobservable. Using Density Functional Theory (DFT), semi-empirical 10 orbital (sp3d5s*) Tight Binding and Ensemble Monte Carlo (EMC) methods we show for the first time that (a) Gunn Effect can be induced in silicon nanowires (SiNW) with diameters of 3.1 nm under +3% strain and an electric field of 5000 V/cm, (b) the onset of NDR in the I-V characteristics is reversibly adjustable by strain and (c) strain modulates the resistivity by a factor 2.3 for SiNWs of normal I-V characteristics i.e. those without NDR. These observations are promising for applications of SiNWs in electromechanical sensors and adjustable microwave oscillators. It is noteworthy that the observed NDC is different in principle from Esaki-Diode and Resonant Tunneling Diodes (RTD) in which NDR originates from tunneling effect.

Core-Shell III-Nitride Nanowire Heterostructure: Negative Differential Resistance and Device Application Potential

In this work we have studied volt-ampere characteristics of single core-shell GaN/InGaN/GaN nanowire. It was experimentally shown that negative differential resistance effect can be obtained in the studied heterostructure. On the base of numerical calculation results the model describing negative differential resistance phenomenon was proposed. We assume this effect to be related with strong localization of current flow inside the nanowire and emergence of Gunn effect in this area.

Сигнальные и шумовые параметры автодинов с мягкой импедансной характеристикой активного элемента (обзор)

The general expressions for an analysis of signal and fluctuation parameters and characteristics of an autodyne oscillator are obtained, which is under an influence of the proper reflected emission from a radar object. The oscillator model represented by a parallel connection of an oscillating system and an active element with the soft impedance characteristics, also takes into consideration the internal noises of the active element. The analysis results are presented for dependences of autodyne mentioned parameters and characteristics versus the oscillator operation mode and a value of the “softness” index of its impedance characteristics of the active element. Investigation results are necessary for engineering calculation of parameters and characteristics of the autodyne on the Gunn diode and other active elements base.

Autodyne Effect of the System Involving Two Mutually Synchronized Oscillators under Strong Coupling

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.

SYSTEM OF AUTOMATIC FREQUENCY CONTROL OF HETERODYNE OF THE RADAR RECEIVER WITH MAGNETRON TRANSMITTER

At present, pulsed magnetrons are leaders in the use in the radar transmitters which is caused by the need to generate powerful high-frequency oscillations and to provide a given coverage range. The disadvantages of magnetrons include a significant level of noise and difficulties in implementing frequency control. For this reason, when using automatic frequency control (AFC), problems arise in controlling the frequency of the pulsed magnetron. In view of this, the AFC of heterodyne of the receiver rather than the one of the magnetron is most often used. The heterodyne frequency is maintained such that the receiver is always tuned to the frequency of the received signal. The objective of this paper is to analyze the existing methods for tuning the heterodyne frequency of pulsed radars with a magnetron transmitter, to develop a concept for building a functional layout and its practical implementation. The functional layout of the automatic frequency tuning system of heterodyne in radar receiver with a magnetron transmitter is developed and described in the paper. A frequency discriminator is used in AFC. The frequency discriminator combines the advantages of a single-cycle circuit (simplicity of design and tuning) and a two-cycle circuit (an output voltage equal to zero at the given magnetron frequency, as well as compensation of variations in the amplitude of the input voltage and interference). The practical implementation of the developed system is presented upon the example of millimeter-wave band radar (40 GHz), where a Gunn diode oscillator with varactor frequency tuning is used as the receiver heterodyne oscillator. In this paper, the electric scheme of a new frequency discriminator and its amplitude-frequency characteristic are shown. An intuitive method was used to develop an electrical schematic diagram. The analysis of the developed scheme was carried out using the method of mathematical modeling. Conclusions are drawn about the novelty of the proposed concept of constructing the AFC of heterodyne radar receivers with a magnetron transmitter and its advantages in comparison with known solutions.

Non-Contact Terahertz Inspection of Water Content in Concrete of Infrastructure Buildings

Concrete is the most widely used for construction materials in the world. Water content of concrete is an important parameter in terms durability of concrete structures. Terahertz (THz) waves, for which concrete is a porous and absorbable material, have been studied in order to establish a new non-contact inspection technology for maintenance of concrete structures. In this study, THz transmittance and reflectance of concrete in drying process were measured with a 60 GHz GUNN diode and absorption coefficient is analyzed for concrete with various water contents. It is shown that quantitative detection below 10% is possible for the water content at surface area of concrete.

Gunn Diodes Based on Graded InGaP-InPAs

Gunn Diodes Based on Graded InGaP-InPAs

Core-shell III-nitride nanowire heterostructure: negative differential resistance and device application potential

AbstractIn this work we have studied volt-ampere characteristics of single core-shell GaN/InGaN/GaN nanowire. It was experimentally shown that negative differential resistance effect can be obtained in the studied heterostructure. On the base of numerical calculation results the model describing negative differential resistance phenomenon was proposed. We assume this effect to be related with strong localization of current flow inside the nanowire and emergence of Gunn effect in this area.

Signals Features from Distributed Targets of Autodyne SRR with Simultaneous Pulse Amplitude and Linear Frequency Modulations

A mathematical model for signals description of the autodyne short-range radar (ASRR) with the simultaneous pulse amplitude modulation (PAM) and the linear frequency modulation (FM) is considered. The peculiarities of signal formation are described, which are obtained from the radar distributed object in the form of an ensemble of an arbitrary number of point-type reflectors. Signal calculations are carried out by the offered approach of the step method for the case of two point reflectors on the radar object located at various distances from ASRR. The distinctive signal properties formed at reception of the first and further emissions reflected form the radar object are established. After sending of the probe emission, the reception of the first reflected emission from the set of shining points is accompanied by linear signal superposition formation from separate reflectors. The reception of further reflections causes an appearance of combinational signal interaction from separate reflectors. The character and degree of such an interaction is defined by the feedback parameter of ASRR, which depends on the autodyne frequency deviation and delay time of reflected emission. Results of ASRR experimental investigations with simultaneous PAM and the linear FM are obtained using the oscillating module made on the Gunn diode of 8mm-range.

Tunable Gunn oscillations in a top-gated planar nanodevice

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.

Modeling the semiconductor devices with negative differential resistance based on nitride nanowires

We proposed a numerical model of the Gunn diode and resonant diode based on a single nitride nanowire. Important model parameters needed for development of the considered devices, namely layers thickness, composition and doping level were evaluated. It has been shown theoretically that the single GaN nanowire based Gunn diode is capable to operate in over 1 THz frequency regime.

Review of GaN-based devices for terahertz operation

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.

Thermal Profiles Within the Channel of Planar Gunn Diodes Using Micro-Particle Sensors

This letter describes the use of a novel micro-particle sensor ( ${\sim }3{\mu }\text{m}$ diameter) and infra-red microscopy to measure the temperature profile within the active channel (typically 3- ${\mu }\text{m}$ length and 120- ${\mu }\text{m}$ 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.

Mapping of electromagnetic waves generated by free-running self-oscillating devices

Near-field mapping has proven to be a powerful technique for characterizing and diagnosing antennas in the microwave frequency range. However, conventional measurement methods based on a network analyzer cannot be applied to on-chip antenna devices extensively studied for future wireless communication in the millimeter wave (mm-wave) (30–300 GHz) and terahertz (THz) wave (0.1–10 THz) frequency regions. Here, we present a new asynchronous mapping technique to investigate the spatial distribution of not only the amplitude but also the phase of the electric field generated by free-running, self-oscillating generators including CMOS oscillators, Gunn oscillators, resonant tunneling diodes, and quantum cascaded lasers. Using a photonic-electronic hybrid measurement system, a wide frequency coverage, minimal invasiveness of the field to be measured, and phase distribution measurements with a theoretically-limited sensitivity are simultaneously achieved. As a proof-of-concept experiment, we demonstrate the mapping of a mm-wave (77 GHz) generated by a free-running Gunn oscillator and antenna characterization based on near-to-far field transformation.

Out-of-band disturbance of mm-wave EMI on RF front-ends

The effects of highly out-of-band electromagnetic interference (EMI) on a RF front-end are experimentally evaluated. Signal at 60GHz 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.

Characterization of emitted light from travelling Gunn domains in Al0.08Ga0.92As alloy based Gunn devices

We report room temperature operation of light emitters based on Al0.08Ga0.92As Gunn devices fabricated in a simple bar geometry with wedged-shaped electrodes. High-speed I-V measurements reveal that, at the threshold of negative differential resistance region at around 3.8 kV/cm, current instabilities, i.e., Gunn oscillations, are created with a 3.8 ns period. Both edge and surface light emission are observed when the device is biased at an electric field of onset of the negative differential resistance (NDR) region at around 3.8 kV/cm and the intensity of the light exponentially increases at applied fields just above NDR threshold likewise in a conventional laser. The origin of the light emission, which has peak wavelength is around 816 nm corresponds to the band-gap energy of Al0.08Ga0.92As, is recombination of electrons and holes generated by impact ionisation process in travelling space charge domains, i.e., Gunn domains. We demonstrate that, with increasing applied field, the amplitude of Gunn domains increases which is a result of the enhanced generation of electrons and holes via impact ionisation. The intensity of the emitted light is observed to be dependent on applied electric field. At low electric fields, light intensity increases linearly then, when applied electric field reaches the onset of NDR region, increases exponentially. Besides, as applied field is increased, full width at half maximum (FWHM) of emitted light decreases to 56.5 nm from 62 nm, evolving into higher selective emission line in wavelength. The light emission from the device is determined to be independent of the polarity of the applied voltage. A comparison of surface emission and edge emission characteristics of the waveguided device are different from each other. Edge emission has higher electroluminescence intensity and better spectral purity than surface emission with well-defined longitudinal modes of Fabry-Pérot cavity, which indicates that, in such a device, lasing action arises from the recombination of excess carriers generated via impact ionisation in travelling Gunn domains. Besides, the edge emission peak of waveguided Al0.08Ga0.92As Gunn device at 4.1 kV/cm is split into two peaks with FWHM of 8 and 6 nm as well as neighbouring sharper minor peaks due to stimulated emission dominates by building-up photons in the cavity. Our results reveal that the proposed Gunn device can be a promising alternative to conventional diode lasers with its simpler design, only one type doped active region and voltage polarity-independent operation, but the duty cycle has to be chosen small enough to make the device operate at room temperature.

The Microwave Sources for EPR Spectroscopy

Rapid development of many scientific and technical disciplines, especially in material science and material engineering increases a demand for quick, accurate and cheap techniques of materials investigations. The EPR spectroscopy meets these requirements and it is used in many fields of science including biology, chemistry and physics. For proper work, the EPR spectrometer needs a microwave source, which are reviewed in this paper. Vacuum tubes as well as semiconductor generators are presented such as magnetron, klystron, traveling wave tube, backward wave oscillator, orotron, gyrotron, Gunn and IMPATT diodes. In this paper main advantages of gyrotron usage, such as stability and an increased spectral resolution in application to EPR spectroscopy is discussed. The most promising and reliable microwave source is suggested.

A tracking microwave wideband band reject filter using antiphase locking

ABSTRACTThis paper reports implementation of a wideband microwave band reject filter (BRF) at a centre frequency of 10 GHz which is based on a new principle of out of phase locking of a pair of Gunn oscillators by a reflected signal. The measured 3-dB bandwidth of the BRF is 486 MHz which is 4.86% of the centre frequency of the BRF with a rejection ratio of 7.08 dB. The bandwidth lies in between narrow band and ultrawide band domain.

Local mechanical stress relaxation of Gunn diodes irradiated by protons

The aim of the work is studying the impact of Gunn diodes thermocompression bonding conditions upon their resistance to being radiated with protons of various energies. It was established that the tough conditions of Gunn diodes thermocompression bonding results in local mechanic stresses introduced into the active layer of the device, reduction of electron mobility because of the faults introduction and, subsequently, to reduction of operating current, power of UHF generation, percentage of qualitative units production and general reduction of production efficiency of the devices with required characteristics. Irradiation of Gunn diodes produced under the tough conditions of thermocompression bonding with protons which energy is (40–60) MeV with an absorbed dose of (1–6)·102 Gy does not practically reduce the radiation resistance of Gunn diodes produced with application of the given technique. This technique can be recommended for all semiconductor devices on the base of GaAs, which parameters depend significantly upon the mobility of the electrons, to increase the efficiency of production.

Physical processes in Gunn diode and energy balance

Physical processes in Gunn diode and energy balance