Effects of Device Geometry and Illumination on Gunn Threshold Voltage and Gunn Oscillation Properties in GaAs Gunn Devices

We fabricate submillimeter-sized GaAs Gunn devices to study the effects of device geometry and illumination on the Gunn threshold voltage and the Gunn oscillation properties. Threshold voltage reduction is observed in wedge-shape-tapered devices and is attributed to the electric field focusing effect towards the narrower end of the devices at the cathode. In addition, illumination could alter the local electron concentration and the global electric field profile of the devices. This leads to a modulation of the Gunn threshold voltage, as well as the magnitude and the coherency of the Gunn oscillations, with the modulation being dependent on the illumination position. The experimental findings of the effects of device geometry and illumination are further corroborated with finite element method simulation of the electric field profile along the devices.