Gunn Diode Research Articles

Terahertz Spectrum Analyzer Based on Fourier Transform Interferometry

A Fourier transform terahertz (THz) spectrum analyzer is demonstrated based on a Martin–Puplett interferometer in the frequency range of 0.1–1.5 THz. High dynamic ranges are achieved at room temperature using a Fermi level-managed barrier diode as the detector. Correction for the frequency dependence of power measurements is achieved using a high-pressure mercury lamp by assuming blackbody radiation. The absolute reference level is determined to be 1 mW by comparing with a calibrated power meter at 0.11 THz using a Gunn oscillator as a reference source. Moreover, the power linearities are evaluated by measuring the reference attenuator at different power levels. Consequently, dynamic ranges are quantitatively verified up to 45 dB within the linearity of 0.2–4.9 dB at frequencies of 0.11, 0.22, and 0.33 THz. Harmonics measurements of the Gunn oscillator are also demonstrated.

Excitation of Short Electric Monopulse in Nitride Films with Negative Differential Conductivity

The excitation of short electric monopulses of space charge waves with wide frequency spectrum of terahertz range in nitride films has been theoretically investigated. The excitation of these pulses with duration ≤ 5 ps and high peak values of electric fields is possible in n-GaN or n-InN films of submicron thickness in the presence of negative differential conductivity. The simulation of nonlinear dynamics of pulses was performed with due regard for the nonlocal dependence of the drift electron velocity on the average electron energy. Optimal values of the applied constant electric fields and equilibrium electron concentration for excitation of monopulses are specified. The monopulse dynamics is weakly dependent on the film width and also on the value and waveform of input excitation pulses. Short electric monopulses differ from domains of strong electric field in Gunn diodes built on bulk crystals with negative differential conductivity.

Design and optimization of a tunable W‐band subharmonic cavity based Gunn diode oscillator using computer‐aided design technique

In this work, a systematic computer-aided design technique is proposed to minimize the fabrication iteration for the design and development of W-band subharmonic Gunn diode oscillator with wideband tunable bandwidth at W-band. Gunn diode based single diode oscillator structure was divided into passive and active parts to facilitate the modeling of the component on appropriate simulation environment. Resonating structure and package of Gunn diode are modeled as passive circuit in high frequency structure simulator (HFSS). To satisfy the oscillator design equation, disc-post resonating structure is tuned in HFSS and its S-parameters are collaborated with the model of Gunn diode in advanced design system. Magnitude and phase of reflection coefficient (S11) is observed to ascertain the desired frequency of oscillation. Proper tuning of disc-post structure is done on simulation platform, which reduces the fabrication complexity and cost as well. The measurement results validate the models designed using EM and circuit simulator. The measured maximum stable RF power without any fabrication iteration is 14.2 dBm. A tunable bandwidth of 4 GHz with power output ripple of ±1 dB is measured by using a movable backshort.

Remote Control of the Surface Movement of an Object Using a Two-Channel SHF Autodyne Generator

In this paper, we describe a method for restoring reflector motion using a radio-wave signal from a super high frequency (SHF) autodyne generator based on a Gunn diode. The proposed method consists in sequential emission and reception of an electromagnetic SHF signal reflected from an object using two channels that differ in electrical length providing the π/2-phase shift of interference signals. With this method, there is no ambiguity in determining the amplitude of reflector movement and no need to determine the initial phase of the detected signal.

Design and Characterization of a Ground-Based Absolute Polarization Calibrator for Use with Polarization Sensitive CMB Experiments

We present the design and characterization of a ground-based absolute polarization angle calibrator accurate to better than 0.1∘ for use with polarization sensitive cosmic microwave background (CMB) experiments. The calibrator’s accuracy requirement is driven by the need to reduce upper limits on cosmic polarization rotation (CPR), which is expected to be zero in a large class of cosmological models. Cosmic polarization effects such as cosmic birefringence and primordial magnetic fields can generate spurious [Formula: see text]-modes that result in non-zero CMB [Formula: see text] and [Formula: see text] power spectra that are degenerate with a misalignment of detector orientation. Common polarized astrophysical sources used for absolute polarization angle calibration have not been characterized to better than 0.5∘. Higher accuracy can be achieved through self-calibration methods; however, these are subject to astrophysical foreground contamination and inherently assume the absence of effects like CPR. The deficiencies in these two calibration methods highlight the need for a well-characterized, polarized source. The calibrator we present utilizes a 76-GHz Gunn oscillator coupled to a frequency doubler, pyramidal horn antenna, and co-rotating wire-grid polarizer. A blackened optics tube was built around the source in order to mitigate stray reflections, attached to a motor-driven rotation stage, then mounted in a blackened aluminum enclosure for further reflection mitigation and robust weatherproofing. We use an accurate bubble level in combination with four precision-grade aluminum planes located within the enclosure to calibrate the source’s linear polarization plane with respect to the local gravity vector to better than the 0.1∘ goal. In 2017, the calibrator was deployed for an engineering test run on the POLARBEAR CMB experiment located in Chile’s Atacama Desert and is being upgraded for calibration of the POLARBEAR-2b receiver in 2018. In the following work, we present a detailed overview of the calibrator design, systematic control, characterization, deployment, and plans for future CMB experiment absolute polarization calibration.

On increasing power of short InGaPAs graded-gap Gunn diodes

Background. The problem of development of the terahertz range with solid state devices remains relevant today. Gunn diodes, IMPATT diodes, resonant tunneling diodes and others are used as active elements. At frequencies above 100 GHz, these devices have a number of physical problems that limit maximum operation from above. One of the possibilities of creating high-frequency Gunn diodes is the use of various graded-gap multicomponent semiconductor compounds. Gunn diodes based on such compounds have higher generation efficiency and, accordingly, output power. Objectives. Multicomponent semiconductors, the fractional composition of which varies in space, can improve the interaction of the electric field and electrons in devices operating on the effect of intervalley electron transfer. To achieve the best effect, such a semiconductor should have an optimal coordinate dependence between the nonequivalent valleys of the conduction band. Therefore, the aim of the work is to investigate the dependences of the effective generation of current oscillations in the terahertz range based on a graded-gap semiconductor Ga1-x(z)Iny(z)Py(z)As1-y(z). Materials and methods. Using mathematical modeling n+ - n - n+ Gunn diodes based on a graded-gap semiconductor Ga1-x(z)Iny(z)Py(z)As1-y(z) with active region length being 1,0 µm and the concentration of ionized impurities in it being 9×1016 cm–3 are considered. The study was carried out based on the solving Boltzmann kinetic equation for a three-level Г–L–X model of intervalley electron transfer. The resulting system of equations is solved numerically and allows one to get the dynamic distribution of the concentration of charge carriers, their energy, current density, electric field strength, and the voltage drop across the diode. Results. It is shown that in graded-gap diodes based on Ga1-x(z)Iny(z)Py(z)As1-y(z) some domain current instability mode can be implemented. Unlike similar devices based on homogeneous semiconductors, such as GaAs, InP or Ga0,5In0,5As, in diodes based on graded-gap Ga1-x(z)Iny(z)Py(z)As1-y(z) undamped current oscillations occur. The maximum power of the main mode of such oscillations is 19 mW at a frequency of 95 GHz. Higher harmonics are present in the oscillations spectrum: the power of the second harmonic is 1,6 mW, and that of the third is 0,3 mW. The frequency and power of self-oscillations in graded-gap diodes depends on the composition of the semiconductor compound both in the anode and in the cathode and is observed at optimal values of the applied voltage. Conclusions. Graded-gap Gunn diodes based on Ga1-x(z)Iny(z)Py(z)As1-y(z) with active region length being 1,0 µm and the concentration of ionized impurities in it being 9×1016 cm–3 are able to generate continuous current oscillations in a fairly wide frequency range due to efficient operation at the main, second and third harmonics. The research results can be used in the development of high-frequency devices for various scientific research.

Isothermal measurement of current-voltage characteristics of Gunn diodes with reflection of their discontinuities and hysteresis

Requirements to the measuring setup are formulated, which make it possible obtaining isothermal current-voltage (I-V) characteristics of the Gunn diode with reflection of their discontinuities, region of negative differential resistance, and hysteresis. The influence of the inductance of the test pulses, source on the occurrence of self-excitation in the connecting transmission line is investigated. The maximum permissible values of the inductance of the test signal source are indicated. Operation of the measuring circuit without self-excitation was experimentally achieved in most of the region with negative differential resistance. The isothermal I-V characteristics of the Gunn diode were measured with a controlled systematic error due to the comparing the measurement result with the developed model of the I-V characteristic.

Autodyne signal features of frequency-locked microwave oscillators

The research results on the autodyne signal formation in microwave oscillators, which are exposed under the impact of the proper reflected emission and, at the same time, of the external frequency-locked signal are presented. The basic relations are obtained for signal analysis under the condition of the quasistatic target movements. The theoretical research results are confirmed by experimental data obtained on the example of an oscillator made on the basis of the 8mm-range Gunn diode.

Dynamic characteristics of frequency-locked autodynes

The results of research into the dynamic characteristics of microwave oscillators under the influence of both their own reflected radiation and external synchronising effect are presented. The basic relations for the analysis of signals during fast movement of the target are obtained, when the signal period is comparable to the autodyne response time constants. The results of numerical modelling of the characteristics are confirmed by the experimental data obtained on the example of an oscillator based on the Gunn diode of the 8-mm range.

Thermal Modeling of the GaN-based Gunn Diode at Terahertz Frequencies

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.

Effect of the Conductive Channel Cut-Off on Operation of n+–n–n+ GaN NW-Based Gunn Diode

Nowadays modern science and technology require development of efficient electromagnetic emitters covering far GHz and THz ranges. Semiconductor elements with negative differential resistance (NDR) such as Gunn diodes based on GaAs and InP are well-established powerful microwave emitters. In this work the Gunn diode structure based on single GaN nanowire with the potential of THz device development was proposed and investigated both theoretically and experimentally. According to the results of the numerical modeling, the Gunn generation can be obtained in the proposed geometry. Dependence of the doping concentration on the NW length necessary for the electrons domain formation was obtained. The nanostructures were grown via molecular beam epitaxy technique. Contacts to single nanowires were fabricated with the combination of e-beam lithography and thermal evaporation. It was shown experimentally that the volt-ampere characteristics of the GaN nanowire structure possess current saturation region. Experimental results correspond well to proposed numerical model.

Current-Induced Spin Polarization in Nonmagnetic Semiconductors

The use of spontaneous electron spin polarization in nonmagnetic semiconductors avoids the transport challenges of electron spin injection from magnetic materials as well as packing constraints of small magnets in a dense array. Although the focus of rearch on the spontaneous spin polarization of electrical current has been on spin-orbit fields and their effects, in principle a moving electron gas can be unstable to forming spin-polarized distributions via carrier scattering processes that are independent of the carrier spin. The two required elements for such current-induced spin polarization without spin-orbit interactions are (1) the presence of built-in spatially-varying electric fields, either naturally forming (as in the Gunn effect) or extrinsic (as in a junction with spatially dependent doping) and (2) energy-dependent carrier scattering processes. As spin-orbit interactions are not required for this effect, it should occur in inversion-symmetric materials like silicon that lack zero-field spin splittings and materials like zinc oxide and gallium nitride that lack significant spin-orbit interactions.

Polarization agile self‐oscillating active integrated antenna for spatial modulation wireless communications

AbstractThis article proposes a new design concept of active integrated array antennas having oscillation and modulation functions for spatial modulation wireless communication systems. Several configurations of the active integrated array antennas are proposed and discussed. The proposed active integrated antennas provide polarization modulated radio waves with a simple structure. A polarization switchable ring‐slot active integrated antenna employing Gunn oscillators is designed and experimentally demonstrated as an example of the proposed concept. The prototype active integrated antenna successfully switched its polarization angle between ±45°. The proposed active integrated antenna concept was found to be feasible.

An electrical equivalent circuit to simulate the output power of an AlGaAs/GaAs planar gunn diode oscillator

AbstractThe 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.

The Mechanism of Superfast Switching of Avalanche <inline-formula> <tex-math notation="LaTeX">${S}$ </tex-math> </inline-formula>-Diodes Based on GaAs Doped With Cr and Fe

The results of theoretical and experimental investigation of charge carrier transport in avalanche S-diodes based on $\pi $ - $\nu $ -n and $\pi $ -n structures are presented. High-ohmic layers of the diodes were made by diffusion of deep chromium and iron acceptors into n-GaAs. It is shown that recharge of the deep acceptors in the avalanche regime should lead to expansion of the space charge region into the $\pi $ -layer and formation of step-type current–voltage characteristics rather than the S-type. It has been found experimentally that the switching of the S-diode is superfast (the time of switching is less than the transient time of the carriers through the active region). The obtained results are in contradiction with the earlier proposed mechanism of deep-level recharging. Thus, this mechanism has been revised. The comparison of the obtained results with the literature data allows one to find the only mechanism of superfast switching, which is associated with generation of collapsing field domains due to the Gunn effect under the avalanche breakdown condition. According to the experiment, the switching time of S-diodes depends on the applied voltage and the type of the deep-level impurity. The S-diodes can operate in relaxation oscillator and sharper circuits. The use of the S-diodes in a sharper circuit with a moderate voltage rate of 1011 V/s allows generating the voltage pulses with amplitude of 700 V and a rising edge of 250 ps at a load of $50~\Omega $ .

Theoretical Model for Negative Differential Conductance in 2D Semiconductor Monolayers

A simple theoretical model of electron heating in a system with two valleys is applied for the first time 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 a possibility to fabricate Gunn diodes of a new generation based on the structures concerned. Such diodes are capable of generating frequencies of an order of 10 GHz and higher, which makes them attractive for many practical applications.

Coherent Summation of Wave Fields of Nanosecond Gunn Oscillators with Initial Phases Fixed by the Leading Edges of Electric Pulses from Synchronized Modulators

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.

Ultrafast electron dynamics reveal the high potential of InSe for hot-carrier optoelectronics

We monitor the dynamics of hot carriers in InSe by means of two photons photoelectron spectroscopy (2PPE). The electrons excited by photons of 3.12 eV experience a manifold relaxation. First, they thermalize to the electronic states degenerate with the $\bar M$ valley. Subsequently, the electronic cooling is dictated by Fr\"ohlich coupling with phonons of small momentum transfer. Ab-initio calculations predict cooling rates that are in good agreement with the observed dynamics. We argue that electrons accumulating in states degenerate with the $\bar M$ valley could travel through a multilayer flake of InSe with lateral size of 1 micrometer. The hot carriers pave a viable route to the realization of below-bandgap photodiodes and Gunn oscillators. Our results indicate that these technologies may find a natural implementation in future devices based on layered chalcogenides.

Interferometrically enhanced sub-terahertz picosecond imaging utilizing a miniature collapsing-field-domain source

Progress in terahertz spectroscopy and imaging is mostly associated with femtosecond laser-driven systems, while solid-state sources, mainly sub-millimetre integrated circuits, are still in an early development phase. As simple and cost-efficient an emitter as a Gunn oscillator could cause a breakthrough in the field, provided its frequency limitations could be overcome. Proposed here is an application of the recently discovered collapsing field domains effect that permits sub-THz oscillations in sub-micron semiconductor layers thanks to nanometer-scale powerfully ionizing domains arising due to negative differential mobility in extreme fields. This shifts the frequency limit by an order of magnitude relative to the conventional Gunn effect. Our first miniature picosecond pulsed sources cover the 100–200 GHz band and promise milliwatts up to ∼500 GHz. Thanks to the method of interferometrically enhanced time-domain imaging proposed here and the low single-shot jitter of ∼1 ps, our simple imaging system provides sufficient time-domain imaging contrast for fresh-tissue terahertz histology.

Main principles of developing exploitation models of semiconductor devices

The paper represents primary tasks, solutions of which allow to develop the exploitation modes of semiconductor devices taking into account complex and combined influence of ionizing irradiation and operation factors. The structure of the exploitation model of the semiconductor device is presented, which is based on radiation and reliability models. Furthermore, it was shown that the exploitation model should take into account complex and combine influence of various ionizing irradiation types and operation factors. The algorithm of developing the exploitation model of the semiconductor devices is proposed. The possibility of creating the radiation model of Schottky barrier diode, Schottky field-effect transistor and Gunn diode is shown based on the available experimental data. The basic exploitation model of IR-LEDs based upon double AlGaAs heterostructures is represented. The practical application of the exploitation models will allow to output the electronic products with guaranteed operational properties.