Contact and temperature effects in Gunn oscillators.

This study is concerned with contact properties of longitudinal and transverse (planar) Gunn devices. A description is given of the fabrication techniques developed for these devices. The transverse structure allows non-parallel electrodes to be used and also the addition of extra electrodes. Frequency tuning was investigated for both concentric electrode and three terminal devices. Tuning ranges of several GHz were observed by variation of anode bias voltage from concentric electrode diodes operating in the transit-time mode. The three terminal devices, which had a Schottky Barrier electrode between the cathode and anode, produced up to 2 GHz electronic tuning with variation of the bias voltage on the third electrode. Cavity controlled operation considerably reduced these tuning ranges. Two domain paths were possible for the three terminal devices and the tuning mechanisms for these are discussed. The frequency drift with ambient temperature was studied on longitudinal devices. These had n+ GaAs contacts to eliminate the overriding negative slope caused by alloyed metal contacts. At full power output, frequency drift rates were between -1 and -2 MHz/°C in a lambda/2 coaxial cavity. However by decoupling the load to reduce the power by about 2 dB, average drift rates were reduced to less than 100 KHz/°C. These results were attributed to the delayed domain and quenched domain modes respectively. Fourier analysis of the current waveform for each mode gave qualitative agreement with experiment