We fabricated and examined current limiting effect for InP Gunn diodes with stable depletion layer mode operation of diodes for high efficiency Gunn oscillators. Current limiting at the cathode was achieved by a shallow Schottky barrier at the interface. We discussed fabrication procedure, the results for negative differential resistance and rf tests for InP Gunn diodes. It was shown that the fabricated Gunn diodes have the output power of 10.22 dBm at a frequency of 90.13 GHz. Its input voltage and corresponding current were 8.55 V and 252 mA, respectively.

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 µm. The distance between the anode and cathode varied from 60 µm to 68 µm depending on the cathode size. Also, we designed a structure with a constant distance between the anode and cathode of 10 µm. 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.