Negative resistance and c.w. oscillation of the transit-time transistor

Negative resistance and c.w. microwave oscillation (5.4 mW at 5.7 GHz) have been observed with the transistor transit-time oscillator. The agreement of these observation with theoretical calculations and the possible advantages of this new component are discussed.     

Silicon pνn avalanche transit-time diodes

Negative resistance characteristics have been observed in the range 3-12 GHz in silicon pvn diodes using avalanche transit-time operation (IMPATT diodes). The diodes, made by a single boron diffusion into epitaxial wafers, had breakdown voltages from 40 to 100 volts. A few hundred diodes all showed, quite reproducibly, microwave negative resistance. Measurement by swept-frequency reflection showed that the negative resistance was present over wide frequency ranges. Oscillation was observed when the diode was put in the coaxial and waveguide "cavities." The oscillation could be tuned over a wide frequency range. The maximum output observed is 30 mW at 11 GHz with 1.7 percent efficiency. Cooling experiments indicated that substantially larger output is possible by proper engineering of the heat disposal. The spectrum width of oscillation, when the diode is reasonably well tuned, ranged from 100 to slightly below 5 kHz. The load impedance into which the diode can oscillate changes from capacitive to inductive, going through a maximum as the oscillation frequency increases. The diodes were found to have so-called microplasmas.     

High-frequency oscillations of p++-n+-n-n++avalanche diodes below the transit-time cutoff

According to Read, n⁺⁺-P⁺-i-P⁺⁺diodes should oscillate at special high frequencies determined by carrier transit time in the space-charge layer. Oscillations not affected by transit time were observed with p⁺⁺-n⁺- n-n⁺⁺silicon diodes. The corresponding current-voltage characteristic revealed a negative resistance setting in at a critical current. Theoretical considerations show that one-sided avalanche injection in n⁺⁺-p⁺-p⁺⁺structures may lead to a slight negative resistance for carrier concentrations smaller than the impurity concentration and for certain widths of the depletion layer. This type of negative resistance disappears in n⁺⁺-p⁺-i-P⁺⁺structures, but with increasing injection multiplication is induced in the intrinsic layer. Therefore the carrier space-charge is reduced and a negative resistance appears at a critical current density. The onset of this second injection is an upper current limit of the Read transit-time mode. The frequency range of oscillations due to avalanche space-charge feedback generally will not be separated from the range of transit-time oscillations. Thus, it must be judged carefully which mechanism is responsible for observed high-frequency oscillations. On the other hand, space-charge feedback may give additional stability to the transit-time mode.     

240-325-GHz GaAs CW fundamental-mode TUNNETT diodes fabricated with molecular layer epitaxy

Gallium arsenide (GaAs) transit-time diodes with tunnel injection of electrons (TUNNETT) with transit-time layer thickness of 100 and 150 nm were fabricated with molecular layer epitaxy (MLE). Continuous-wave fundamental-mode oscillation in the frequency range of 240 to 325 GHz in metal rectangular resonant 0.86 /spl times/ 0.43 mm size (WR-3) cavities was obtained. Output power of -13 dBm was generated at 322 GHz. The fundamental mode operation, as well as experiments on different impedance matching configurations, suggest that it is possible to develop fundamental mode TUNNETT generators for the frequency range of 350 GHz to 1 THz. Operation of the TUNNETTs confirms device quality of the MLE.     

An analysis of wide-band transferred electron devices

The trapping conditions of a high-field domain at the anode are studied by varying doping density, applied bias voltage, and doping notch depth and width near the cathode. It is shown that the frequency band of negative conductance of the trapped-domain mode depends significantly on the doping density, and a diode having the doping density of 3 × 10¹⁵/cm³exhibits the negative conductance over the wide range from 4 GHz to 42 GHz. The upper frequency limit of the negative conductance is due to the series resistance in the low-field region and the lower limit is determined by carrier transit-time effects in high-field region. The operation mode of a trapped-domain diode will change into a traveling dipole or accumulation mode from a trapped-domain mode depending on the doping density and the operation frequency for a large-signal operation.     

Chaotization of Oscillations in a Single-Frequency Millimeter-Band Impact Avalanche and Transit-Time Diode Oscillator under the Influence of a Low-Frequency Harmonic Oscillation

The change in the oscillation spectrum of an oscillator based on an impact avalanche and transit-time (IMPATT) diode of the 7-mm range under the action of a low-frequency harmonic oscillation (3 MHz) in the supply circuit of the diode is studied experimentally. It is demonstrated that, if the low-frequency oscillation amplitude exceeds the trigger negative voltage and the working point in the diode volt–ampere characteristic is located either near the trigger current (trigger negative voltage) or far from it, pulsed oscillation mode is established and, consequently, oscillations are chaotized.     

CW oscillations in GaAs planar-type bulk diodes

CW Gunn oscillations at frequencies from 0.5 GHz to over 1 GHz have been obtained with GaAs bulk diodes constructed from an epitaxial n layer grown on semi-insulating substrates. Observations of current waveforms have been made for both transit-time and delayed-domain modes. CW microwave power of 12 mW has been obtained at 0.9 GHz.     

太赫兹二次谐波回旋振荡器时域多模分析

推导了时域多模公式并结合频域单模理论对394 GHz二次谐波回旋管进行了模式激励及模式互作用分析.当工作电压为15 kV,工作磁场为7.185 T,工作电流为0.25 A时,在频域单模稳态计算中TE_(261-)~2不能起振,工作模式TE_(261+)~2达到稳定振荡;时域多模仿真结果显示TE_(261+)~2和TE_(261-)~2均能在393.87 GH稳定振荡,TE_(261+)~2在最终振荡中占主导地位,其输出功率和效率分别为136.8 W、3.6%,两者获得的工作模式的输出特性完全吻合.     

Transit-time oscillator with velocity-limited injection

The basic theory of a space-charge transit-time oscillator is outlined in which phase lag of current is caused by using low-velocity injection. Large negative resistances are anticipated at microwave frequencies, giving generation of moderate power levels with low-noise operation. Approximate design calculations for a representative idealised structure 100 ?m square, based on silicon and operating at a frequency of 10 GHz, suggest a negative resistance of ?50 ? and a negative Q factor of -?/2, with a maximum output power of about 1 W and an efficiency of about 7%.     

High-efficiency continuous oscillations in silicon IMPATT diodes below the transit-time frequency

C.W. room-temperature operation of silicon IMPATT diodes at the first subharmonic of the transit-time frequency has been observed in a high-efficiency mode. Efficiencies as high as 8.8% at 5GHz with 1.2 Wc.w. have been achieved with current densities no more than 1480A/cm2.     

（英）用于MW级回旋管的TE34,10模圆柱高频腔体设计

采用TE34,10-模式开展了140 GHz兆瓦级圆柱回旋管腔体的设计和优化,并分析了工作模的模式竞争情况。由于两个邻近模式TE33,10-和TE31,11+的竞争TE34,10-未能在高效率区稳定振荡,使得输出功率显著降低。为了抑制模式竞争计算了工作模和两个竞争模的滞回曲线,结果表明,TE34,10-能够在磁场由其低功率振荡区下降时对竞争模形成抑制,而在磁场由低到高时则由于竞争模的率先起振反而被竞争模所抑制。基于此设计了由5.59 T下降至5.51 T的时变磁场曲线,在此磁场下开展了包含42个模式在内的多模时域计算,结果表明竞争模式被有效抑制,工作模在此磁场曲线下能够稳定获得0.96 MW的稳定输出功率,对应的电子效率为36.7%,频率为140 GHz。     

Pump power dependence of ruby laser starting and stopping time

Experimental results from a number of small ruby lasers show a linear relationship between the pump power and the inverse of the time delay between pump flash and the onset of laser oscillation. These experimental results are quantitatively predicted by a simple rate-equation analysis, yielding a single theoretical curve with no adjustable parameters and in good agreement with the experiments. Additional evidence is also presented verifying the onset at higher pump powers of additional "bouncing-ball" or "light-pipe" modes of oscillation in ruby rods with polished side walls. These additional modes account, in particular, for the abrupt cessation of laser output after an anomalously short duration of laser action, as is typically observed in such rods. These anomalous modes, which are usually not well coupled to the detection circuitry, apparently suppress the normal mode of oscillation once they begin and limit the available output energy in the normal mode. The anomalous modes are eliminated by roughening the sides of the rod, after which normal duration of laser action is observed. The laser stopping time is also predicted with reasonable accuracy by the rate-equation analysis.     

Microwave circuit characteristics of bulk GaAs oscillators

The microwave circuit characteristics of bulk GaAs transit-time mode and limited space-charge accumulation (LSA) mode oscillators have been evaluated experimentally and theoretically. Experimental measurements were performed with a waveguide-coaxial microwave circuit having two experimental degrees of freedom in which the circuit radiation impedance at the device contacts was evaluated by a dyadic Green's function method. Experiments conducted in three rectangular waveguide circuits at fixed bias voltage have established that the LSA mode frequency tuning range is determined by the magnitude and variation of the circuit series inductive reactance XLrelative to the device low-field resistance R0. At a bias voltage which is twice threshold the tuning range is given by1/2.4leq X_{L}/R_{0}leq 2.4. No fixed, linear equivalent circuit characterizes the LSA mode. Analysis and experimental results indicate that the device impedance of small-signal transit-time mode oscillators changes from a passive parallel RC impedance well below threshold to an impedance just above threshold which can be approximated by a series RLC circuit. The series L and C decrease linearly with transit-time mode harmonic order number.     

半绝缘GaAs光电导开关中光激发电荷畴的猝灭畴模式

在半绝缘GaAs光电导开关中发现了光激发电荷畴的猝灭畴模式. 分析指出畴猝灭是由于畴在渡越中开关的瞬时电场低于畴的维持电场引起的,并指出在开关电场低于非线性光电导开关阈值电场条件下,在到达阳极前畴的猝灭可导致开关输出电流的振荡频率高于畴的渡越时间频率. 根据开关工作电路条件及畴特性给出了猝灭畴模式的等效电路,计算了相应的电路参数,计算结果与实验基本吻合. 该研究为提高光注入畴器件的振荡频率及工作效率提供了理论和实验依据.     

Operation of a resistive-gate MESFET oscillator in thesingle-domain transit-time mode

Resistive-gate (RG) MESFET oscillators having gate sheet resistance of 30 kΩ/sq are operated in the single-domain transit-time mode. Frequencies from 6 to 28 GHz are observed, inversely proportional to channel length. Unlike a lateral Gunn diode, operation is essentially independent of drain-to-source voltage, indicating that channel conditions are controlled by the potential drop along the resistive gate. The authors conclude that contiguous domains cannot form in the channel unless the gate sheet resistance is reduced to about 3 kΩ/sq     

Characteristics of the mode converter of Gyrotron FU CW GII radiating Gaussian beams in both the fundamental and second harmonic frequency bands

Gyrotron FU CW GII, the second gyrotron of the Gyrotron FU CW G-series with an internal quasi-optical mode converter, was recently developed at the Research Center for Development of Far-Infrared Region, University of Fukui (FIR FU) [Y. Tatematsu et al., J. Infrared, Millimeter, Terahertz Waves 35, 169 (2014)]. The design oscillation mode of this gyrotron is TE_8,3 with a corresponding frequency of 393.4 GHz in the second harmonic cyclotron resonance. We observed oscillations of different modes including fundamental harmonic modes in the 200-GHz band upon varying the strength of the magnetic field in the cavity. Radiation patterns corresponding to these modes emitted from the window were Gaussian although the internal mode converter was designed for the TE_8,3 mode. The directions of the radiated Gaussian beams were found to depend on the oscillation modes with a relation similar to that obtained for another gyrotron that was also equipped with a mode converter. This relation is explained based on geometrical optics. Moreover, numerical calculation with the electromagnetic wave code developed in FIR FU confirmed the same relation. The observed features of the Gyrotron FU CW GII show that it can serve as a unique power source with two frequency bands at 200 and 400 GHz. This result provides a way of developing multiple-frequency gyrotrons.     

Millimeter-wave orotron oscillation--Part II: Experiment

Experimental observation of orotron oscillation is reported in the frequency band from 53 to 73 GHz. The output power in a quasi-CW mode and beyond an output window is approximately 100 mW at a beam current of 90-100 mA. Oscillation has been observed on several modes of the open resonator of the orotron, with starting currents ranging from 35 to 82 mA. The electronic tuning transconductance within a single mode was measured by mixing the orotron signal with another signal from a klystron, yieldingdf/dV = 0.25MHz/V. The spectrum of the orotron output signal was also measured by this method, and the linewidth was determined to be less than 0.4 MHz at 70 GHz.     

Nonlinear analysis of the avalanche transit-time oscillator

The nonlinear operating characteristics of the avalanche transit-time oscillator are studied by means of Fourier-series representation. For optimum operation, the oscillator must be designed such that start-oscillation conditions are satisfied simultaneously at the first and the second harmonic of the desired oscillation frequency. Under those conditions the oscillation frequency does not depend on the dc bias current; the signal level increases smoothly with bias current. For large signals, the diode exhibits negative resistance for frequencies substantially below the avalanche frequency; the oscillation frequency therefore may be below the avalanche frequency corresponding to the dc bias current required for large-signal operation. A condition for attaining large-signal operation is that the product of drift-zone capacitance and total load resistance must be small compared to the oscillation period; this condition also yields small starting currents. The output power at the oscillation frequency is obtained explicitly in terms of diode and external circuit parameters. The maximum attainable output power is limited by parasitic series resistance and by permissible RF voltage swing as compared to dc bias voltage. The best power-impedance product is obtained by choosing the transit angle equal to 0.74 π. In practice, it may be advantageous to choose a smaller value for the transit angle, in order that the tuning condition for the second harmonic may be more easily satisfied. The dc-to-RF conversion efficiency in principle is linearly proportional to the dc current density; the maximum efficiency again is limited by parasitic series resistance and by permissible RF voltage swing.     

A low-frequency analog for a Gunn-effect oscillator

After a brief introduction to the Gunn effect and an explanation of the proposed equivalent circuit of the Gunn diode, a low-frequency (5 Hz) lumped-circuit analog is described. The analog is able to simulate the initiation and circuit quenching of the domain, the transit time of a dipole domain, and the dynamic negative-resistance characteristic associated with the domain. Thus the analog can qualitatively account for many properties of the dipole domain modes. A short section also shows how, within certain limitations, the LSA mode can be investigated by means of the analog. The analog enables the behavior of the Gunn diode to be studied under various forms of loading, and the results to be related to a wide range of actual diodes in microwave circuits by a simple scaling process. The sciencies of various modes can be compared. Photographs are presented of an oscilloscope display showing the relevant current and voltage waveforms (including the domain voltage) for a pure resistive load, a parallel resonant load, and a series inductive load. The provision for a direct display of domain voltage means that a particularly clear visual distinction is possible between transit-time and circuit-quenched modes of oscillation. Tuning by variation of the external load is demonstrated; the importance of the semiconductor's current peak-to-valley ratio and of the choice of transit time in determining the efficiency in a given mode is illustrated. A possible explanation for the reported observation of subharmonics is provided by the analog, on the basis of alternate modes, i.e., a cycle of circuit-quenched operation followed by a cycle of transit-time operation. The limitations of the analog are discussed together with ways in which some of them could be overcome.     

光电双基区晶体管的工作机理

通过分析光电双基区晶体管(PDUBAT)内部载流子的二维传输过程,获得它的物理模型,得出PDUBAT是个新型光控振荡器的结论,并依此模型给出了它的等效电路,利用SPICE程序得到的一系列计算结果与实验结果是一致的.结合这些计算结果,完整解释了PDUBAT产生耦合、负阻、振荡的物理过程.给出了起振电压(输出电流峰值电压)、振荡频率随光强变化的关系式,定性解释了相应的实验结果