The mechanism and device applications of high field instabilities in gallium arsenide

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Abstract
The paper reviews the present understanding of the behaviour of high field instabilities in GaAs and discusses the device prospects in the light of work carried out to obtain a phenomenological model for the Gunn effect.The moving high field domain, which forms in n-type GaAs when the applied field of several thousand volts per cm exceeds a sharply-defined threshold value, has been studied over a wide range of drift paths, but particularly in long samples. For applied voltages below the threshold value a novel technique of triggered operation has been used whereby just one cycle of operation is produced. A model for domain formation which has been derived from the results is characterized by two well-defined field values. The ohmic current flowing in the material when a domain is present is associated with the lower field value. The transient current in the period between the decay of one domain and the creation of the next is associated with the higher field level. An important consequence of the model is that it suggests a direct proportionality between the voltage appearing across the domain at a given bias field and the length of the sample. This conclusion has been confirmed by measurements on samples in the range 0 025 in to 0 10 in where domain amplitudes from 60 V to 300 V respectively have been observed. The results are in agreement with Ridley's theoretical prediction of domain formation arising from a voltage controlled bulk negative resistance.The implication of the model on the use of the device for power generation and modulation at microwave frequencies are discussed and the results of experiments studying the change of the main parameters under varying ambient conditions are given.

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