Millimeter-wave Gunn oscillator in series operation

The feasibility of series operation of a Gunn-diode oscillator in a millimeter-wave range is demonstrated. Oscillator output power and its dc-to-RF conversion efficiency can both be increased substantially by operating two Gunn diodes in series. Output power from two diodes in series operation is higher than twice the output power obtained from one individual diode. We report that the pulsed output power from two GaAs Gunn diodes in series operation reaches 4.4 W at a frequency of 33.2 GHz.     

High-efficiency operation of a Gunn oscillator in the domain mode

An examination of the problem of obtaining high-efficiency operation of a Gunn oscillator is given in this paper. The results are based on an assumed form of I-V characteristic of the Gunn diode, the ideal voltage and current waveforms being found for high-efficiency operation. The theory for a square wave of current through and voltage across the diode is worked out in detail and shown to predict the experimental results well. It is shown that a voltage waveform consisting of only a fundamental and second harmonic component could give efficiencies in the 20-28 percent range, as much as a factor of 3 larger than for a simple sinusoid. This is a reasonable approximation to the ideal voltage waveform, which is a half sinusoid of voltage. In this paper the charge and discharge time of the domain is neglected. An estimate of these times is given in the Appendix, and it is shown that the efficiency theory should be relevant to operation with diodes for whichnL gg 10^{12}cm^-2. The theory may also describe certain types of "LSA mode" operation.     

High-efficiency operation of transferred-electron devices in the hybrid mode

Efficiencies up to 22% at peak-power levels of 60 W in X band have been obtained with transferred-electron devices. These efficiencies are in good agreement with values computed from hybrid-mode theory. A waveguide circuit which permits independent adjustment of the resistive and reactive components of the circuit impedance at the device-package terminals is described. This circuit provides a match for devices with widely different impedances. The close agreement between the theoretical and experimental values of efficiency indicate that both high material quality and an optimum impedance match between the device and the circuit have been achieved.     

Thermal effects of the operation of high average power Gunn devices

A lumped thermal resistance model is described for GaAs Gunn and LSA diodes. Thermal resistances are defined for the active layer, contact layer, bond interface, package and heat sink. This permits the calculation of tha maximum device temperature TM= T0+ P ΣiRiand the critical temperature difference across the active layer ΔTA= PRA. A transient analog incorporates thermal time constants Ti= RiCito consider high duty cycle pulsed operation. The carrier mobility is modeled as varying as1/Tin the range from 300 to 500°K. This permits thermal measurements based upon changes in resistance. The thermal calculations were also in agreement with blackbody infrared data. The mobility decline with temperature is shown to act as a link between the thermal profile and device performance. A thermally induced avalanching point, as well as device efficiency, are influenced by the peak-to-valley current ratio. This ratio is reduced from its theoretical value of over 2:1 by the active layer resistivity ratiobar{partial}/partial_{max}. Thus thermal gradients in the active layer act to create mobility gradients which alter the observed peak-to-valley ratio. The steps necessary for maintaining high average power efficient operation require low thermal resistances to minimize the active layer temperature gradients and a high current drop back ratio. Total experimental thermal resistances of 6.5°C/watt for an X-band CW diode and 17°C/watt for a thick LSA diode have been observed and fit the model presented.     

Submillimeter-wave InP Gunn devices

Recent advances in design and technology significantly improved the performance of low-noise InP Gunn devices in oscillators first at D-band (110-170 GHz) and then at W-band (75-110 GHz) frequencies. More importantly, they next resulted in orders of magnitude higher RF output power levels above D-band and operation in a second-harmonic mode up to at least 325 GHz. Examples of the state-of-the-art performance are continuous-wave RF power levels of more than 30 mW at 193 GHz, more than 3.5 mW at 300 GHz, and more than 2 mW at 315 GHz. The dc power requirements of these oscillators compare favorably with those of RF sources driving frequency multiplier chains to reach the same output RF power levels and frequencies. Two different types of doping profiles, a graded profile and one with a doping notch at the cathode, are prime candidates for operation at submillimeter-wave frequencies. Generation of significant RF power levels from InP Gunn devices with these optimized doping profiles is predicted up to at least 500 GHz and the performance predictions for the two different types of doping profiles are compared.     

Planar Schottky-gate Gunn devices

Gunn devices, with a Schottky diode as control electrode, were fabricated and investigated. The experimental results are compared with calculations, which are also outlined, and agreement between theory and experiment is found to be satisfactory. A jitter in domain nucleation is shown to be due to fluctuations in the anode voltage.     

Bias circuit oscillations in Gunn devices

A theoretical and experimental study of low-frequency oscillations in the bias circuit of short (nominally 12 µ) Gunn devices is presented. Sinusoidal oscillations and relaxation oscillations including damped sinusoids and exponentially decaying pulses have been observed. The frequency, pulse width, and repetition rate are adjustable with bias voltage, bias circuit impedance, and the impedance of the microwave circuit. This behavior, as well as the conditions for stable bias, is explained in terms of an average terminal i-v characteristic for those devices which exhibit a terminal current drop. The oscillation amplitude is determined by the shape of this i-v curve. Pulses have been observed with subnanosecond rise times, peak voltages of 35 volts and adjustable pulse widths ranging from 3 to 200 ns for typical driver pulse widths of 100 to 500 ns. The sinusoidal frequencies were adjustable in the range of 300 to 550 MHz. The microwave output was in X-band and was self modulated by the bias circuit oscillations. The measured waveforms agree well with theory.     

Simple integrated circuit with Gunn devices

This letter describes the structure and electrical performance of a simple integrated digital circuit on GaAs using Gunn devices, which is capable of operating at up to 2 Gbit/s. A directed transfer of domain pulses within the circuit, which is almost free of reactive effects, is achieved by employing Schottky-barrier diodes.     

Negative-resistance amplifiers using three-terminal Gunn devices

Negative-resistance amplifiers have been realised using three-terminal Gunn devices. Both transmission and reflection amplifiers were made, with the central frequency in the range 100?540 MHz for the transmission type and in the range 390?425 MHz for the reflection type. The maximum gain obtained reached about 53dB with a noise figure of about 20dB for a transmission-type amplifier operated at 140 MHz.     

High-efficiency phosphorescent polymer light-emitting devices

In this paper, we describe the performance of polymer light-emitting devices (PLEDs) that are based on phosphorescent polymers involving a carbazole unit and an iridium-complex unit. The PLEDs exhibit red, green or blue emission, depending on the phosphorescent polymer used in the emissive layer. We achieved highly external quantum efficiencies of 5.5%, 9% and 3.5% in respective red, green and blue PLEDs by selecting the electron transport material for the emissive layer and optimizing the content of the iridium-complex unit in the phosphorescent polymer chain. Furthermore, we demonstrated white emission in PLEDs by using blue-phosphorescent and red-phosphorescent polymers. An external quantum efficiency of 4.5% was obtained for this emission.     

Delay structures with planar Gunn devices

A pulse delay obtained with the aid of the domain travelling effect in Gunn devices is described. For this purpose, the planar Gunn devices contain, in addition to a trigger electrode, a capacitive electrode for coupling out the signal. Experimental results are given for the single component and a monolithic integrated cascade circuit. The devices are appropriate for constructing dynamic shift registers in the sub-nanosecond range.     

Frequency/temperature characteristics of Gunn devices

The variability and large magnitude of the frequency/temperature coefficient of Gunn oscillators has limited the application of these devices. The letter outlines a program of experiments and computer simulations aimed at achieving an understanding of the basic ?f/?T mechanism and thus producing a deep stable oscillator. Our simulations successfully predict observed trends in the ?f/?T behaviour of Gunn devices with both alloyed metal and n+ regrown contacts. The results of our study show that stable oscillators with a small loaded Q factor and near maximum power output are realisable.     

High-efficiency operation of avalanche-diode oscillators

A mode of operation for avalanche-diode oscillators is described which depends for its application upon the controlled attainment of reverse-current densities in the range 104?107 A/cm2. It gives a current-controlled negative-resistance characteristic and leads to efficiencies of at least 60%. With present technology, it should be possible to operate the mode up to 10GHz.     

Gallium arsenide on sapphire Gunn effect devices

The epitaxial growth of single-crystal GaAs on an insulating sapphire substrate, recently reported, has been used in the fabrication of Gunn effect devices.     

GaAs planar Gunn digital devices with subsidiary anode

GaAs planar Gunn digital devices with a subsidiary anode are proposed. The subsidiary anode is effective in suppressing the pathological growth of the high-field layer near the anode. Gate triggering by small input pulses below 100 mV is possible     

GaAs planar Gunn digital devices by sulphur-ion implantation

Schottky-barrier-gate Gunn-effect devices have been fabricated in n-type layers produced by sulphur-ion implantation into Cr-doped semi-insulating GaAs substrates. The device performance was examined and a satisfactory gate trigger sensitivity was obtained under d.c. bias conditions.     

Current spreading at contacts to planar Gunn devices

The implications of current constriction at a planar contact to GaAs are inferred from the results of a simpler case (current flow to a small conducting cylinder). It is argued that a number of the pathological properties of Gunn diodes can be explained in terms of this mechanism.     

GaAs planar Gunn diodes for DC-biased operation

The difficulty in obtaining CW oscillations in GaAs planar Gunn diodes has been found to be due to distortion of the field distribution by a field-enhanced trapping effect. A tapered active region is proposed to compensate for the effect due to the trapping. By adopting the geometry, coherent CW Gunn oscillations have been obtained successfully with reasonable reproducibility.     

Frequency modulation of three-terminal Gunn devices by optical means

The three-terminal Gunn device first reported by Petzinger et al. has been frequency modulated by shining light either on the n-type gallium arsenide or the p-n junction of the device. Different sensitivities are achieved in those two modes of operation. While the device was oscillating in the bias-circuit mode at about 500 MHz, frequency variations linearly dependent on the intensity of the light have been observed in both modes of operation. The maximum shifts about 2 percent of the oscillating frequency, has been measured at a light intensity of 25 mW/cm²and when light was directed only on the n-type gallium arsenide. Higher-frequency shifts have been observed in the nonlinear region. The device has demonstrated capability of detecting very short light pulses, ∼ 50 ns, generated by GaAs laser.