Gunn Diode Research Articles

Fabrication and Characterisation of GaAs Gunn Diode Chips for Applications at 77 GHz in Automotive Industry

GaAs-based Gunn diodes with graded AlGaAs hot electron injectorheterostructures have been developed under the special needs in automotive applications.The fabrication of the Gunn diode chips was based on total substrate removal andprocessing of integrated Au heat sinks. Especially, the thermal and RF behavior of thediodes have been analyzed by DC, impedance and S-parameter measurements. Theelectrical investigations have revealed the functionality of the hot electron injector. Anoptimized layer structure could fulfill the requirements in adaptive cruise control (ACC)systems at 77 GHz with typical output power between 50 and 90 mW.

Influence of the variband-layer thickness on the energy and frequency characteristics of In x(z)Ga1 − x(z)As Gunn diodes

The operation of variband-Inx(z)Ga1 − x(z)As Gunn diodes with an active-region length of 2.5 µm and an n+-n cathode contact is studied by using a two-temperature model of electron intervalley transfer in a varib-and semiconductor. It is established that, in diodes, dipole domains or accumulation layers may be formed depending on the variband-layer thickness. The use of variband Inx(z)Ga1 − x(z)As in the active region with an appropriate variband-layer thickness allows one to enhance the output power and the generation efficiency by a factor of approximately 1.5 and to increase the width of the frequency range of the diode operation approximately twofold as compared to that of an In0.2Ga0.8As-based diode.

Electric field and carrier concentration distributions in the semiconductor under photorefractive Gunn effect

In the framework of the one-dimension field model of semiconductor simultaneosly subjected to the action of carrier-warming electric field and two quasi- monochromatic light waves the authors have numerically calculated the spatial-temporal distributions of inner electric field Е(x,τ) and conductivity band electrons n(x,τ) in dependence on external control parameters (intensity of the incident light waves, their wave vector, external electric field and doping impurity concentration). It was found that the device operating on the base of photorefractive Gunn effect may be controllably switched between three following operation modes: low- and high-light wave intensity as well as a transition mode. The influence of the external control parameters on the Е(x,τ) distribution was determined for each mode in question. It was shown that one could efficiently control the refractive index increment n Δ by means of proper change of the control parameters.

Centrifugal distortion analysis of the millimeter-wave spectrum of 2-fluorobenzonitrile and ab initio DFT calculations

The ground state ( ν = 0) rotational spectrum of 2-fluorobenzonitrile has been reinvestigated in the frequency range 40.0–99.0 GHz. The millimeter-wave spectrometer used is a source-modulated system combined with a free space glass cell. Millimeter-wave radiation has been produced using a Gunn diode and frequency doubler combination. High J and K −1 ( J ⩽ 49 and K −1 ⩽ 18) transitions have been measured and accurate rotational and centrifugal distortion constants have been determined. Finally, the experimental values were compared with the corresponding values calculated at the HF/DFT-B3PW91/6-31g(d,p) level of theory. A very good agreement has been found.

Numerical Simulation of Nonlinear and Parametric Oscillations in a Semiconductor Resonator Structure

The rigorous mathematical modeling of nonlinear oscillations in microwave strip-slot resonator structure (RS), loaded with a distributed planar Gunn diode, is based on the solution of the threedimensional diffraction boundary problem, formulated rigorously taking into account the full set of Maxwell's equations and the nonlinear equation of transport carriers in a semiconductor. Using our numerical approach to determine the bifurcation points of the solution of nonlinear Maxwell's equations, the transition region from the stationary regime of the nonlinear semiconductor device behavior (i.e., the frequency multiplication and the stable para- metric amplification) to the generation (the onset of self-oscillations) caused by the instability process in the distributed Gunn diode, was simulated taking into account constrained geometries of strip-slot RS.

Deterministic Simulation of the Boltzmann--Poisson System in GaAs-Based Semiconductors

In this work we present a deterministic numerical scheme solving the one-dimensional Boltzmann--Poisson system for semiconductor materials with a complicated band structure such as GaAs. The model is based on a system of two kinetic equations for the electron population in each of the relevant valleys coupled through the Poisson equation to consider the self-consistent potential. Interaction of electrons with the crystal is taken into account by treating the most important inter- and intravalley scattering mechanisms in GaAs. The numerical scheme follows the main ideas in [J. A. Carrillo, I. M. Gamba, A. Majorana, and C.-W. Shu, J. Comput. Phys., 184 (2003), pp. 498-525] already developed for Si-based devices. The newest numerical features are the intervalley scattering, the singularity of the kernels of impurities, and optical polar phonon scattering. The charge conservation of the scheme is achieved by a suitable discretization of the collision operator within the accuracy of the middle-point integration rule. A detailed study of this numerical scheme is made by showing results on the bulk material, numerically validating the results by comparison to direct simulation Monte Carlo (DSMC) results, and testing our results for diodes and Gunn oscillations.

Memory Processes in the Response of Plants to Environmental Signals

Plants are sensitive to stimuli from the environment (e.g. wind, rain, contact, pricking, wounding). They usually respond to such stimuli by metabolic or morphogenetic changes. Sometimes the information corresponding to a stimulus may be “stored” in the plant where it remains inactive until a second stimulus “recalls” this information and finally allows it to take effect. Two experimental systems have proved especially useful in unravelling the main features of these memory-like processes. In the system based on Bidens seedlings, an asymmetrical treatment (e.g. pricking, or gently rubbing one of the seedling cotyledons) causes the cotyledonary buds to grow asymmetrically after release of apical dominance by decapitation of the seedlings. This information may be stored within the seedlings, without taking effect, for at least two weeks; then the information may be recalled by subjecting the seedlings to a second, appropriate, treatment that permits transduction of the signal into the final response (differential growth of the buds). Whilst storage is an irreversible, all-or-nothing process, recall is sensitive to a number of factors, including the intensity of these factors, and can readily be enabled or disabled. In consequence, it is possible to recall the stored message several times successively.In the system based on flax seedlings, stimulation such as manipulation stimulus, drought, wind, cold shock and radiation from a GSM telephone or from a 105 GHz Gunn oscillator, has no apparent effect. If, however, the seedlings are subjected at the same time to transient calcium depletion, numerous epidermal meristems form in their hypocotyls. When the calcium depletion treatment is applied a few days after the mechanical treatment, the time taken for the meristems to appear is increased by a number of days exactly equal to that between the application of the mechanical treatment and the beginning of the calcium depletion treatment. This means that a meristem-production information corresponding to the stimulation treatment has been stored in the plants, without any apparent effect, until the calcium depletion treatment recalls this information to allow it to take effect. Gel electrophoresis has shown that a few protein spots are changed (pI shift, appearance or disappearance of a spot) as a consequence of the application of the treatments that store or recall a meristem-production signal in flax seedlings. A SIMS investigation has revealed that the pI shift of one of these spots is probably due to protein phosphorylation. Modifications of the proteome have also been observed in Arabidopsis seedlings subjected to stimuli such as cold shock or radiation from a GSM telephone.

Monitoring the Frozen State of Freezing Media by using Millimeter Waves

We built a device that uses millimeter waves to monitor the water/ice state of samples. It consists of a 35-GHz Gunn oscillator producing an output power of about 10 mW, two horn antennas, and a power meter. We confirmed that the difference in the absorption of water and ice was significant, and we could discriminate and monitor the frozen states of water and cell medium containing dimethyl sulfoxide (DMSO). We also measured the absorption of frozen cell media containing different DMSO concentrations. These experiments demonstrate the possibility of applying millimeter waves to optimize and monitor crystal structure for various combinations of cell medium and DMSO.

New technological possibilities to prepare InP epitaxial layers, as well as ohmic and barrier contacts to them, and the properties of microwave diodes made on their basis

A novel technological approach to fabrication of n-InP autoepitaxial films LPE-grown on porous n + -InP substrates, as well as ohmic and barrier contacts to them using (quasi)amorphous TiBx interstitial phases, is proposed. We demonstrate the advantages of TiBx−n-n + -n ++ -InP Schottky-barrier diodes made on porous substrates over those made on the standard rigid substrates, as well as the possibility to make Gunn diodes (intended for the 120−150 GHz frequency range) on the InP epitaxial structures grown on porous substrates.

Novel technological possibilities for growth of GaAs autoepitaxial films, and properties of Gunn diodes made on their basis

Novel technological possibilities for growth of GaAs autoepitaxial films, and properties of Gunn diodes made on their basis

An unusual nonlinearity in current-voltage curves of a bidimensional electron gas at low temperatures

Electrical characterization of a bidimensional electron gas transport has been investigated. Three AlGaAs∕GaAs heterostructures have been used for the study. Hall measurements have been performed at 4.2K and current-voltage characteristics at fixed temperatures between 4.2 and 300K. Measurements have been made using a four-point probe method. A saturation of the current at weak electric fields was observed in the range of low temperatures (<100K). The channel conductivity, the contact resistance, the electron mobility and the bidimensional electron gas density were determined. Electron drift velocities were deduced from current-voltage curves at the beginning of the saturation regime at 4.2K and compared with those found in the literature. The saturation, giving weak velocity, is related to impurity and alloy scatterings. Drift velocities close to the Fermi velocity are related to the Gunn effect. A Schottky effect has been observed at low temperatures (<100K) when the electron transport is perpendicular to the direction leading to the saturation of the current. This Schottky behavior indicates degradation of Ohmic contacts in the Au∕Ni∕Ge structure constituting the source and the drain.

Digital holography at millimetre wavelengths

In this paper, we describe a method for wavefront reconstruction at millimetre wavelengths using off-axis holography, a frequently used image recording technique at visible wavelengths first demonstrated in the 1960’s. Millimetre radiation has been highlighted recently in the imaging of non-conducting materials and objects, which often show significant transparency at these long wavelengths, even though opaque at visible and infrared wavelengths. Holography provides a method for recording a lens-less image of an object thus reducing loss of spatial frequency information, which is important for obtaining maximum resolution at long wavelengths. An experimental arrangement based on a simple form of Fresnel off-axis holography is described, with the object illumination and reference beams derived using two radiating horn antennas fed by a single coherent source (a Gunn diode oscillator operating at 100GHz – wavelength 3mm) via a 3dB cross-guide coupler. The process is discussed in the context of imaging and in the validation of millimetre wave radiation sources (horns). We show that the entire fields from these and other components can be analysed using computational optics with data derived from a single measurement obtained using inexpensive equipment.

Tunable-frequency high-field electron paramagnetic resonance

A tunable-frequency methodology based on backward wave oscillator sources in high-frequency and -field EPR (HFEPR) is described. This methodology is illustrated by an application to three non-Kramers transition metal ion complexes and one Kramers ion complex. The complexes are of: Ni(II) ( S = 1) as found in dichlorobistriphenylphosphanenickel(II), Mn(III) ( S = 2) as found in mesotetrasulfonatoporphyrinatomanganese(III) chloride, Fe(II) ( S = 2) as found in ferrous sulfate tetrahydrate, and Co(II) ( S = 3/2) as found in azido(tris(3- tert-butylpyrazol-1-yl)hydroborate)cobalt(II). The above Ni(II) and Mn(III) complexes have been studied before by HFEPR using the multifrequency methodology based on Gunn oscillator sources, but not by the present method, while the Fe(II) and Co(II) complexes presented here have not been studied by any form of HFEPR. Highly accurate spin Hamiltonian parameters can be obtained by the experimental methodology described here, in combination with automated fitting procedures. This method is particularly successful in determining g-matrix parameters, which are very difficult to extract for high-spin systems from single frequency (or a very limited set of multi-frequency) HFEPR spectra, but is also able to deliver equally accurate values of the zero-field splitting tensor. The experimental methods involve either conventional magnetic field modulation or an optical modulation of the sub-THz wave beam. The relative merits of these and other experimental methods are discussed.

The U-Band Pattern Steerable Active Patch Antenna

Combing the active antenna concept with the reconfigurable antenna technique, a pattern steerable active patch antenna is presented and designed in this paper. A Gunn diode is used to generate the millimeter wave signal and loaded at the centre of the patch antenna. This antenna system has a stable oscillation frequency f : 44.0GHz and operates as a quasi-Yagi patch antenna. The radiation patterns of the antenna can scan in the whole horizontal plane with 3-db beam width by using four reconfigurable states and the radiation main beam of each state directs to the elevation angle 59° in the elevation-plane. The antenna can be applicable to the millimeter wave half-duplex communication and identification systems.

Millimeter Wave Gunn Diode Oscillator Design Based on FDTD Method*

In this paper, a millimeter wave Gunn diode oscillator is analyzed and designed by the finite-difference time-domain (FDTD) method. The design results indicate that the oscillator has an oscillation frequency of 45.0GHz and a higher oscillation voltage. Based on the circuit equations and an integral transform, an improved matrix method is utilized for the oscillator design. This method is also extended to model the hybrid network which is constructed by the high order linear elements and the nonlinear elements with arbitrary connections. The experience shows that the improved FDTD method is stable with the time step length Δt based on the Courant condition.

Measurements of Near-Infrared Frequency Mixing by Metal–Semiconductor Point-Contact Diodes

The performances of metal-semiconductor point-contact diodes as mixers in the near-infrared region were tested. Preliminary experiments were performed in order to phase-lock two diode lasers at 850 nm a few hundred gigahertz apart. GaSb, InAs, and InSb as semiconductor layers were used. The frequency bridge between the two lasers was covered by a Gunn diode frequency locked to a 1-GHz oscillator. A novel phase-lock circuit was tested on two diode lasers 72 GHz apart.

Dynamic Range of High Temperature Superconducting Josephson Detecting Systems at Millimeter-Wave Band

YBCO grain boundary Josephson junctions (GBJJ's), with the normal-state resistance (R/sub N/) around 1 /spl Omega/ and I/sub C/R/sub N/ product of less than 2 mV at 45 K, where I/sub C/ is the critical current of the junction, are used to study the dynamic range of high temperature superconducting (HTS) Josephson detecting systems at millimeter-wave band. A compact pulse tube cryocooler (PTC), or a liquid helium cryostat (LHC), or a liquid nitrogen cryostat (LNC) provides the necessary low temperature environment for the operation, while Gunn oscillators together with doubler generate signals at the frequencies of 50, 98, 196 GHz whose amplitude can be adjusted by a series of calibrated attenuators. By changing the junction parameters, operating frequencies, and the cryocooler or cryostat, we have carefully looked at the dynamic range of the system. For a measuring channel bandwidth of 1 Hz, the dynamic range is around 38 dB which is determined basically by the preamplifier. This indicates that the PTC does not introduce excess noise compared with other kinds of cryostats such as LHC's or LNC's. A measuring channel bandwidth up to 1 MHz can be helpful if fast measurements are needed.

Fabry–Perot Gunn laser

A truly monopolar GaAs Fabry–Perot cavity Gunn laser is demonstrated. The device is grown by metalorganic chemical vapor deposition on a semi-insulating GaAs substrate and consists of an n=4.6×1017cm−3 doped GaAs active layer sandwiched between the AlxGa1−xAs(x=0.32) waveguiding layers. The operation of the device is based on the band to band recombination of impact-ionized nonequilibrium electron-hole pairs in the propagating high field domains in the Gunn diode, which is placed in a Fabry–Perot cavity, and biased above the threshold of negative differential resistance. Lasing from the device is observed at temperature T⩾95K. The maximum power emitted from the device is P=25.4μW at λ=840nm and T=95K.

Stimulated emission from a Fabry‐Perot cavity GaAs/Ga 0.68 Al 0.32 As Gunn laser

A monopolar GaAs Fabry-Perot cavity laser based on the Gunn effect is demonstrated. The optical intensity of the edge emission is 30 watt/cm' at an applied electric field of 4.4 kV/cm. The n type GaAs active layer (n=5×10 1 7 cm - 3 ), placed in a wave-guide has a longitudinal cavity length of 213-226 μm. Excess carriers are produced by impact ionization within the propagating space charge (Gunn) domains. The electroluminescence spectra show a strong dependence on the number of domains in transit. The growth of the lasing mode coincides with the increase of the accumulation density of excess carriers in the Gunn device.

Microwave Invasion Through Anti-Reflecting Layers of Dielectrics at a Millimeter Wave Irradiation to Living Bodies

Microwave invasion into living bodies through a millimeter wave catheter irradiation is described. As radiation sources for millimeter wave irradiation tests both Impatt oscillator (IO) and a Gunn oscillator were used. Irradiated samples are cow livers and living rats. A newly designed wave-guide vent antenna (WVA) with an anti-reflecting layer (ARL) is used as a launcher for the irradiation and the reflectance measurements. The correlation between the denaturation of the tissue and the reflectance from the WVA is studied in detail.