Junction Diameter Dependence of Oscillation Frequency of GaN IMPATT Diode Up to 21 GHz

An experimental study on the effects of junction capacitance and current density on the oscillation characteristics of GaN single-drift-region (SDR) impact ionization avalanche transit-time (IMPATT) diodes were carried out using GaN p+-n abrupt junction diodes of various diameters, 200, 150, and $100 \mu \text{m}$ , with a depletion layer width of $2 \mu \text{m}$ . The fabricated diodes showed a clear avalanche breakdown at 315 V and a pulsed microwave oscillation with a peak output power exceeding 30 dBm. The oscillation frequency depended on junction diameter and current density. It was widely modulated from 8.56 to 21.1 GHz with decreasing junction diameter and increasing current density. The highest oscillation frequency was obtained with a current density of 13.8 kA/cm2 and a junction diameter of $100 \mu \text{m}$ . A numerical calculation based on Read-type small-signal theory was carried out and found to well explain the experimental results.