Design and fabrication of planar GaAs Gunn diodes

We studied planar graded-gap injector GaAs Gunn diodes designed for operation at 94 GHz. Two types of planar Gunn diodes were designed and fabricated. In the first diode, a cathode was situated inside a circular anode with a diameter of 190 mu m. The distance between the anode and cathode varied from 60 mu m to 68 mu m depending on the cathode size. Also, we designed a structure with a constant distance between the anode and cathode of 10 mu m. In the second diode, the anode was situated inside the cathode for the flip-chip mounting on the oscillator circuits. The fabrication of the Gunn diode was based on ohmic contact metallization, mesa etching, and air-bridge and overlay metallization. DC measurements were carried out, and the nature of the negative differential resistance, the operating voltage, and the peak current in the graded-gap injector GaAs Gunn diodes are discussed for different device structures. It is shown that the structure with the shorter distance between the cathode and anode has a higher peak current, higher breakdown voltage, and lower threshold voltage than those of the structure with the larger distance between the cathode and anode.