B. Culshaw

Invited paper. Avalanche diode oscillators. I. Basic concepts

This is the first of a series of three papers in which the basic physics of IMPATT diodes, their applications and limitations, and their prospects for the future will be discussed. This, the first instalment, concentrates on the underlying physical phenomena and the basic theory of the device. The fundamental semiconductor properties are reviewed, followed by a basic account of the avalanche and drift processes. This leads on to a description of the Read diode and an analysis of the device baaed on the sharp pulse approximation, whore approximate large signal limits are derived. The treatment of the device theory is then extended to give a realistic feel for the impact of various material parameters on device operation. The technique in to examine EACH material parameter as a perturbation on the sharp pulse approximation, and in this MANNER the effects of the following parameters arc examined : (1) The relationship between the r.f. voltage and the electric field distribution throughout the cycle, includin...

Comprehensive models for the analysis of high-efficiency GaAs IMPATT's

High-efficiency GaAs IMPATTs have several distinctive characteristics which have been the subject of considerable theoretical investigation. In general, the approach has been to isolate a particular physical mechanism and consider its effect on the device. In this paper, the interaction between all these effects is discussed in terms of comprehensive models. Accurate numerical results are derived from a full computer simulation of the device. These results provide a number of new insights into device operation, especially the importance of thermal effects. An overall assessment of the numerical results leads to the development of a graphical construction which incorporates the most important physical effects in one simple diagram. This enables a rapid and accurate estimate of the effects of structure, temperature, current density, operating frequency, and RF voltage on the operation of the device. Finally, the models described are used to derive a design procedure for a high-efficiency structure.

Invited paper. Avalanche diode oscillators. II. Capabilities and limitations.

The previous part of this survey described the basic physics of avalanche diodes. This paper considers the optimum design of an IMPATT oscillator and reviews the properties of the conventional device. The physics of high efficiency gallium arsenide diodes is then described, and possible advances upon present designs are discussed. The limitations of avalanche diodes, in terms of power, frequency, noise and stability are then discussed in some detail. Finally the effects of material parameters on device performance are described and the properties of silicon and gallium arsenide are compared.

Invited paper Avalanche diode oscillators III. Design and analysis : the future

This is the final part of this series of papers. In it we develop more intricate versions of the ‘ avalanche plus drift ’ combinations, We examine the double-drift structure, the possibility of a double avalanche structure and outline the properties of a heterojunction device. We continue to discuss possible different materials, including more unusual semiconductors. The remainder of the main part of this paper is devoted to a critical account of the various modelling techniques which may be used to give a theoretical account of the behaviour of the device. In the paper so far, we have used the simplest possible models : these do, of course, have some limitations, and we describe some of these. The potentially most accurate models involve some form of computer simulation. An outline of our present approach to the simulation problem is given, along with a description of some of the pitfalls which the user of this technique may encounter. Finally, three appendices fill in some of the more important omission...

Recovery Of Phase Modulated Signals In Multimode Optical Fibres

Coherent light propagating along a multimode optical fibre may be phase modulated by external disturbances including changes in for instance the pressure or temperature of the medium surrounding the fibre. At the output from a multimode fibre, a direct phase to amplitude modulation conversion effect takes place at the detector, and this signal may be used to detect the presence of the environmental change. However, the phase detection process is intrinsically non-linear and is subject to fading effects. This paper concentrates on describing techniques whereby reliable and consistent phase detection techniques may be implemented by optical means and presents the results obtained in the actual use of some of these techniques.

Fibre optic gyroscopes

Report on 1st conference on fibre optic gyroscopes and related technologies, 9-11 November 1981 at Massachusetts Institute of Technology, Boston, USA.

Physical Mechanisms in High Efficiency Gallium Arsenide Avalanche Diodes

Anomalously high efficiencies have been observed in GaAs avalanche diode structures - approaching twice that predicted for the ideal Read diode. The physical mechanisms which contribute to this observed efficiency enhancement, namely depletion layer width modulation and accelerated carrier flow, are described in this paper. The principles are established using a sharp pulse model, and the discussion is extended to consider the implications for broad pulses. The validity of the analytical approaches is then assessed by comparing the results of analysis with those of a computer simulation of the device, including all the relevant device physics.