EE4101_M_MW1 - EE4101 RF Communications MW1 NATIONAL...

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Page 1 of 4 N ATIONAL U NIVERSITY of S INGAPORE Faculty of Engineering Electrical & Computer Engineering Department EE4101 RF Communications Experiment MW1 GUNN OSCILLATOR 1 OBJECT To become familiar with the operation of the Gunn oscillator and to measure some of its characteristics. 2 INTRODUCTION The Gunn oscillator is called so after a British scientist, J.B. Gunn, who around 1960 was studying high-field effects in semiconductors. When he was measuring the voltage-current characteristics of Gallium Arsenide (GaAs), he discovered very high frequency oscillations when the applied electrical field was in the order of 2000 V/cm. In his own words: “… when I pushed the electric field up to the neighbourhood of 1000 to 2000 V/cm, something entirely unexpected happened. Instead of a simple variation of current with voltage, all hell broke loose – the current started to jump up and down in a completely irregular way that very much resembled electrical noise except that the amplitude was much greater than could be accounted for by any noise mechanism I knew of. The current variations were of the order of amperes rather than the nano-amperes you ordinarily see.” If no notice was taken of the oscillations, the voltage-current behaviour was as in Figure 1. At the voltage Vo the GaAs started to behave similar to a negative resistance. Gunn made a lot of experiments and came to the conclusion that this phenomenon was not a tunnel effect. The tunnelling effect in an Esaki-diode occurs at the contacts, but the Gunn-effect is a bulk (= volume) effect, i.e. something that happens over an extended region. Figure 1. Voltage-current characteristic
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EE4101_M_MW1 - EE4101 RF Communications MW1 NATIONAL...

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