Tunable frequency Gunn diodes fabricated by focused ion beam implantation

Gun diodes have been fabricated in GaAs, where the implanted doping concentration is varied linearly from one contact to the other. The starting material was semi-insulating GaAs, and Si/sup ++/ ions were implanted at 140 keV. The dose was varied from 1*10/sup 13/ cm/sup -2/ to 3*10/sup 13/ cm/sup -2/ over a distance of 80 mu m. The width of the implant was 10 mu m. The frequency of oscillation could be smoothly tuned from 6 to 23 GHz by varying the bias voltage in the range of 25 to 35 V. Identical-geometry but uniformly doped devices exhibited bias-independent frequency of oscillation. Other doping profiles can yield other functions. A numerical model to solve the conservation equations, coupled with Poisson's equation, has been developed to simulate device performance. The solution is performed in the time domain and allows the domain nucleation, motion, and discharge to be observed. Doping profiles that optimize the diode performance can be predicted. >