Transferred Electron Oscillators Research Articles

Observation of transferred-electron oscillations in diamond

The transferred-electron oscillator (TEO), or Gunn oscillator, is a device used in microwave applications, which utilizes the negative differential mobility (NDM) effect to generate continuous oscillations. Recently, NDM was observed in intrinsic single-crystalline chemical vapor deposition (SC-CVD) diamond. The occurrence was explained by the electron repopulation between its different conduction band valleys. This paper presents the results of constructing a diamond TEO based on the NDM effect. A series of experiments have been performed for varying voltages, temperatures, and resonator parameters on three SC-CVD diamond samples of different thicknesses. For the temperature range of 90–300 K, we observe transferred-electron oscillations in diamond.

Publisher's Note: “Investigation of transferred-electron oscillations in diamond” [Appl. Phys. Lett. 108, 212104 (2016)

Publisher's Note: “Investigation of transferred-electron oscillations in diamond” [Appl. Phys. Lett. <b>108</b>, 212104 (2016)

Investigation of transferred-electron oscillations in diamond

The recent discovery of Negative Differential Mobility (NDM) in intrinsic single-crystalline diamond enables the development of devices for high frequency applications. The Transferred-Electron Oscillator (TEO) is one example of such devices that uses the benefit of NDM to generate continuous oscillations. This paper presents theoretical investigations of a diamond TEO in the temperature range of 110 to 140 K where NDM has been observed. Our simulations map out the parameter space in which transferred-electron oscillations are expected to occur for a specific device geometry. The results are promising and indicate that it is possible to fabricate diamond based TEO devices.

Monte Carlo analysis of GaN-based Gunn oscillators for microwave power generation

Monte Carlo studies of transferred electron oscillators based on bulk wurtzite GaN are presented. Two structures have been examined: (i) devices with the conventional single notch structure, and (ii) repetitive structures with serial segments to fashion a “multiple domain” device. Wurtzite material has been chosen because of the higher drift velocity and because analytical expressions for the band structure have recently become available. Performance parameters of interest such as the operating frequency, output power, and conversion efficiency are calculated. Variations due to changes in temperature, biasing voltage, and device length are also included. It is shown that multidomain Gunn diodes can lead to significant improvements in output power over conventional, single-transit structure, and so such multiple GaN diodes merit serious experimental study.

Transient simulation of millimeter-wave circuits incorporating numerical device modeling

A fast convolution-based computational approach is employed to integrate numerical solid-state device simulation with nonlinear millimeter-wave circuit simulation. Unlike previous combined harmonic-balance/device approaches, the high-frequency circuit/physical device response is allowed to evolve in time to its natural steady-state mode of operation, permitting insight into harmonic and parametric energy exchange, stability, load pulling, and frequency tuning effects. To demonstrate this computationally efficient approach, a second-harmonic 150-GHz transferred electron oscillator is simulated using both conventional Gunn and novel stable-depletion-layer InP devices. The integrated device/circuit simulations in the time domain enable us to investigate the formation and buildup of the oscillation modes in detail.

A numerical study of chaos in transferred electron oscillators and amplifiers with the use of an improved computer model

A model of a transferred electron device including reactive circuit elements and realistic boundary conditions is used to study chaos. We find that any simulation of chaos is suspect if the external circuit and cathode boundary conditions are ignored; including them reduces the range of parameters in which chaos occurs. © 1996 John Wiley & Sons, Inc.

A numerical study of chaos in transferred electron oscillators and amplifiers with the use of an improved computer model

A numerical study of chaos in transferred electron oscillators and amplifiers with the use of an improved computer model

A 60-GHz MMIC-compatible TED-oscillator

Experimental results achieved with planar GaAs transferred electron oscillators at V-band frequencies are reported in this contribution. The active devices are MESFET-like structures with a Schottky-gate controlling the electron injection into the drift region. The electron injection is adjusted to a level yielding a frequency independent negative differential resistance which is exploited for millimeter-wave power generation. The highest measured CW output power and efficiency are 6.72 mW and 1.3% at 60.33 GHz, respectively. These results are comparable to those obtained with transistor oscillators which are much more difficult to fabricate due to their extremely small dimensions in the 0.1 /spl mu/m range. >

Simulation of 100-300 GHz solid-state harmonic sources

Accurate and efficient simulations of the large-signal time-dependent characteristics of second-harmonic transferred electron oscillators (TEO's) and heterostructure barrier varactor (HBV) frequency triplers have been obtained. This is accomplished by using a novel and efficient harmonic-balance circuit analysis technique which facilitates the integration of physics-based hydrodynamic device simulators. The integrated hydrodynamic device/harmonic-balance circuit simulators allow TEO and HBV circuits to be co-designed from both a device and a circuit point of view. Comparisons have been made with published experimental data for both TEO's and HBV's. For TEO's, excellent correlation has been obtained at 140 GHz and 188 GHz in second-harmonic operation. Excellent correlation has also been obtained for HBV frequency triplers operating near 200 GHz. For HBV's, both a lumped quasi-static equivalent circuit model and the hydrodynamic device simulator have been linked to the harmonic-balance circuit simulator. This comparison illustrates the importance of representing active devices with physics-based numerical device models rather than analytical device models.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

100-300 GHz Gunn oscillator simulation through harmonic balance circuit analysis linked to a hydrodynamic device simulator

Accurate and efficient calculations of the large-signal AC behavior of second-harmonic InP transferred electron oscillators (TEOs) are presented. This is accomplished by combining a novel harmonic balance circuit analysis technique with a hydrodynamic device simulator employing the temperature dependent drift and diffusion equations. The electron transport simulations include a detailed heat flow analysis to update the temperature profile in the device. The nonlinear circuit analysis utilizes a fixed-point iterative method derived from the robust multiple reflection algorithm. To expedite the process and aid in convergence, an acceleration technique is also employed in this algorithm. The associated reduction in computation time allows for the inclusion of a hydrodynamic treatment of the transferred electron device (TED) using the modified drift and diffusion equations. Comparisons are made with the published experimental data reported by Rydberg on second-harmonic 188 GHz InP TEOs.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Composite anode contact for planar transferred electron devices

In order to prevent the anode contact of transferred electron devices (TEDs) from burning out, a Schottky contact is frequently used. Unfortunately, this approach gives rise to a decrease in efficiency due to the built-in voltage of the Schottky contact. A possible way of avoiding this decrease is to use a composite contact. By combining a short stripe of a Schottky metal with an ohmic contact, the loss of DC power dissipated in the Schottky anode contact is eliminated, thereby maintaining to some extent the depletion layer necessary for preventing the formation of a stationary high field domain at the anode contact. With this approach, a 30% increase in efficiency of a CW operated field effect controlled transferred electron device (FECTED) oscillator at a frequency of 35 GHz has been obtained. The achieved efficiency of 3.8% is, to the authors' knowledge, the highest efficiency obtained with a planar transferred electron oscillator (TEO) at 35 GHz.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Gunn effect in MESFET-like structures

The performance of planar field-effect controlled transferred electron oscillators with different combinations of layer thickness and doping concentration has been investigated. A negative differential resistance has even been obtained with 0.29μm thick 1.6 × 1017 cm-3n-doped samples. This is the first time a MESFET-like active layer has exhibited the Gunn effect and has successfully been operated as a TEO at 36 GHz.

Thermal analysis for improved performance of transferred-electron oscillators

Novel analytical solutions to the heat-flow equation are presented for GaAs transferred-electron devices to be operated in microwave oscillators. Uniform and linearly varying power dissipation density in the active region is considered. The results show that, to reduce operating temperatures, devices should be operated in the heat-sink anode configuration rather than the conventional top-cap anode configuration. This will ensure improved microwave power output from transferred-electron oscillators.

An accurate calculation of the d.c. electrical and thermal characteristics of GaAs transferred-electron devices

A physical model to simulate the d.c. behaviour of GaAs transferred-electron devices has been developed. An accurate calculation of the electrical and thermal characteristics is made possible by solving the semiconductor device equations self-consistently with the heat flow equation. A novel heat flow analysis has been developed to model non-uniform heat generation/absorption across the whole GaAs region including high-low junctions, substrates, buffer and contact regions. Since a thermal current term is included in the current density equation, commonly consisting of drift and diffusion terms only, the analysis is referred to as a drift-diffusion-thermal model. The model is shown to be useful for the thermal design of transferred-electron devices for operation in CW transferred-electron oscillators. In addition to the design of the heat sink configuration, the doping concentration profile of the GaAs region can also be designed to reduce operating temperatures, thereby ensuring improved d.c. microwave conversion efficiency and lifetime.

MIMIC-compatible GaAs and InP field effect controlled transferred electron (FECTED) oscillators

A MIMIC-(millimeter wave monolithic integrated circuit) compatible transferred electron oscillator is investigated which utilizes the frequency-independent negative resistance of the stationary charge dipole domain that forms in the channel of a MESFET. The device structure, analysis, and simulation are described. Devices fabricated from GaAs and InP exhibit very high power levels of 56 mW at 29 GHz and 55 mW at 34 GHz, respectively. Continuous wave power levels are somewhat lower (30 mW).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

IC-compatible 45 mW Ka-band GaAs transferred-electron oscillator

The performance of a planar field effect controlled transferred electron oscillator has been significantly improved by reducing the length of the low field regions near drain and source. 45 mW with 4.3% efficiency at 28.4 GHz and 24 mW with 3.2% at 37.4 GHz have been obtained, which is a factor of 4.5 times larger than was obtained a year ago.

Screened-space-charge transferred-electron oscillators

We describe a novel form of a monolithic semiconductor oscillator in which the space-charge field of a drifting charge packet is modified, by means of the electrostatic boundary conditions of the device, so as to produce no voltage drop across the packet. Under these conditions, we predict that a sequence of narrow, identical, contiguous packets can be formed producing extremely high-frequency oscillations in the 30-300-GHz range, independent of the length of the drift region. This is in contrast to conventional transferred-electron oscillators in which the space-charge-induced voltage drop across either an accumulation region or a dipolar domain limits the drift region to, at most, a single packet at any time, thereby limiting the frequency achievable to packet-transit, -formation, or -decay times. Computer simulations and analytical solutions indicate that the frequency can be tuned electronically over a broad band by controlling the charge-injection level, while the oscillator center frequency depends upon the specific device geometry and the electron transport properties at the applied field. In theory, oscillations as high as 2 THz are not inconceivable.

Self-aligned notched planar InP transferred-electron oscillators

A procedure is described for the fabrication of planar InP transferred-electron oscillators (TEO's). In this procedure, a localized high resistivity region is self-aligned to the cathode contact. The self-aligned structure, which also included a selectively implanted n+ anode, produced a pulsed power output of 220 mW with an efficiency of 9.5 percent at 9.1 GHz and a CW power output of 80 mW with an efficiency of 5.3 percent at 5.5 GHz. This is the highest reported power output and efficiency for a planar transferred-electron device in this frequency range.

Modulation Schemes in Low-Cost Microwave Field Sensors

The use of modulation schemes in short-range microwave field sensors are discussed and in particular the ideas are applied to low-cost self-detecting doppler sensors based on a two-terminal negative resistance diode oscillator which acts as a load variation detector. FM-CW and pulse modulation techniques are described which can lead to improved performance in these sensors, and experimental results of bias modulation, varactor modulation, and pulsed operation of transferred-electron oscillators are presented. Modulation techniques can be applied in order to eliminate false alarms due to unwanted targets by enabling the doppler sensor to measure or discriminate target range, and the potential merits of different schemes based on frequency modulation with linear and sinusoidal modulation patterns are explored. A novel environmental profiling technique is proposed which exploits the response of frequency-modulated sensors to multiple stationary targets for use in a versatile short-range surveillance system employing digital processing techniques. The mechanism of pulsed operation in self-detecting sensors is described, and the effects of temperature variations in the active device, which result in frequency chirp, are considered. The technique of extracting the doppler signal from the pulsed bias current using a pulse cancellation circuit is demonstrated, and the effects of bias current changes during the pulse (due to temperature variations) on the use of this type of circuit are discussed.

Transferred-electron oscillations in In 0.53 Ga 0.47 As

Transferred-electron oscillations were observed and investigated in planar devices of In0.53Ga0.47As. The peak-to-peak magnitude of oscillations with respect to the device current at threshold field was as high as 70%, indicating the peak-to-valley velocity ratio of 3.3:1 for this material. The domain velocity was estimated from the oscillation frequency (2 GHz) and the corresponding device length (40 µm) to be 8×106 cms¯1. The results presented in the letter show a promising prospect for TED applications of this ternary alloy.