Transit Time Devices Research Articles

Efficiency of baritt and dovett oscillators

The large-signal performance of baritt and dovett (double-velocity transit-time) devices is analysed using an analytical model and computer simulations. The predictions agree well with each other and, in the case of baritts, with experimental results. Efficiencies of more than 25% are predicted for some dovett devices.

Noise in microwave, injection, transit time and transferred-electron devices

Noise in microwave, injection, transit time and transferred-electron devices (Gunn, avalanche and baritt diodes) is studied. It is first necessary to describe the semiconductor structures considered and to analyse briefly their microwave properties. Then noise at the small signal levels is considered; for each type of device, optimization of the structure will be discussed. Finally, large signal level operation is studied and for each device, some possibilities to minimize excess noise under large signal conditions will be suggested. For each case, the state of the art of noise performance in 1975 will be given.

Investigations of the Fabrication of Thin Silicon Films for Microwave Semiconductor Transit Time Devices

The fabrication of thin silicon films for microwave semiconductor devices is investigated using polishing and etching methods. With the described bubble etching method the thickness of the Si film can be monitored during etching. Si‐films with a thickness down to 3 μm could be fabricated with this process. The etched films are free of strain and etch pits and are sufficiently plane parallel as required by microwave transit devices. The fabrication of an MnM Baritt diode and a double diffused Impatt diode without substrate is given as example.

Graphical optimization of the doping profile of transit-time devices

The doping profile of transit-time avalanche diodes has evolved from a compromise of technological convenience and the original structure proposed by Read [1]. A technique by which the doping profile my be quickly optimized is described, and it is shown that a four-layer p-n-p-n structure should give the highest efficiency for a transit-time diode. This technique, which my be generalized to other types of device, predicts the maximum power density available from the optimum structure. For a Read-type diode, operating in X band, this is in the region of 40 kW/cm2at an efficiency of around 30 percent. Higher efficiencies are attainable at the expense of output power.

An ultrasonic displacement instrument with greater beam dispersal.

An ultrasonic transit time device was modified to permit close placement of the crystals and to broaden the effective spatial angle of the beam of ultrasound. The device is ideal for chronic animal experiments since its output is linear for displacement and calibration may be performed at any time.

Theoretical and experimental study of GaAs IMPATT oscillator efficiency

This theoretical and experimental study was motivated by a specific need for a solid-state microwave generator with an output efficiency exceeding 20% and focused on the properties of GaAs avalanche transit-time devices. First, the dependence of the ionization rates and drift carrier velocities as a function of electric field and temperature is established. Then several methods of calculation, exact enough to take into account all the important efficiency-limiting effects in the device, are discussed and used to derive theoretical figures for the efficiency of a GaAs IMPATT oscillator, special attention being given to the influence of the doping profile. Finally, the experimental study is described, including device realization and experimentally measured efficiencies, and a comparison between these and the calculated values is done. It is shown that the best calculated performances can reach 30% efficiency and that it is possible to obtain experimentally cw oscillation efficiencies exceeding 20% with GaAs IMPATT devices having special types of doping profile.

Small-Signal Negative Conductance in BARITT Devices

Numerical calculations utilizing a realistic carrier velocity vs electric field relationship have been carried out for the dc current-voltage characteristics and small-signal ac response of abrupt Si p+np+, p+nvp+, n+pn+, and n+pπn+ barrier injection transit time (BARITT) devices. The small-signal ac response of these devices can be represented accurately by the depletion capacitance either in parallel with a negative conductance or in series with a negative resistance. The negative conductance has maximum amplitude for transit angles of approximately 1.55π and dc current density biases of 20–100 A/cm2. A distinct advantage was found in small-signal applications for p+np+ devices over p+nvp+ devices and for n+pn+ devices over n+pπn+ devices.

Noise in avalanche transit-time devices

The work performed on noise in avalanche transit-time devices is reviewed and presented in detail. Both theoretical and experimental results on the noise mechanisms and performance of these devices when employed as oscillators, amplifiers, and self-oscillating mixers are included. Suggestions for further studies in this area are also given.

Basic Principles and Properties of Avalanche Transit-Time Devices

The basic principles and characteristics of the various modes of operation of avalanche transit-time devices are presented. Theoretical and experimental results are also presented in order to indicate the present state of development and the kind of performance which has been achieved in these devices.

A theoretical appraisal of the quenched multiple domain mode in GaAs microwave diodes

Quenched multiple domain (q.m.d.) mode oscillations in bulk GaAs have been analysed to obtain the relationships between efficiency, fundamental-frequency power output, fundamental-frequency negative resistance, and d.c. bias voltage. It is found that this highly efficient mode does not have the limitations of transit-time devices and consequently has a frequency-independent power × impedance product. The results demonstrate that q.m.d. oscillators designed with multiple-tuned circuits can operate at twice the efficiency of those operated in single-tuned circuits.

The Serrodyne Frequency Translator

A serrodyne frequency translator will translate, or shift, the frequency of a signal in a nearly ideal manner. Linear sawtooth modulation of a transit-time device, such as a traveling-wave tube or klystron, is employed to effect the translation. The power output at the translated frequency is practically equal to the capability of the same device operating as an ordinary amplifier. Furthermore, very little power is produced in undesired intermodulation frequency components. Frequency translations of a microwave signal ranging from subaudio frequencies to 57 megacycles have been accomplished. The translation loss for a translation of about 30 megacycles was less than 1 decibel; moreover, each undesired frequency component was suppressed at least 20 decibels. The serrodyne method can be used at nonmicrowave frequencies and with larger fractional frequency shifts, provided modulable transit-time devices having certain properties can be devised. An analysis is given of serrodyne performance as limited by a number of important practical factors. A general spectrum analysis is included which is in a convenient form for a variety of problems in combined AM and PPM (or combined AM and PM) when arbitrary modulating waveforms are used.

Influence of Initial Velocities on Electron Transit Time in Diodes

The transit time spread due to difference in initial velocity in a planar diode has been calculated for the case of nonhomogeneous velocity distribution. The spread is given as a function of the current for two practical cases, the normal diode and an inverted diode (a beam reflected in a diode space). The spread is also given as a function of anode voltage within certain limits. The method may be used to estimate the influence of transit time spread on transit time devices. A special application is described.