Experimental characterization and theoretical analysis of K- to V-band GaN Hi-Lo IMPATT diodes

We report the experimental characterization and theoretical analysis of high-frequency GaN IMPATT diodes featuring a Hi-Lo doping profile. On-wafer small-signal measurements of reflection gain over frequency and temperature confirm IMPATT operation covering Ka through V bands. Temperature-dependent reverse I–V measurements also confirmed avalanche breakdown as the dominant breakdown mechanism. Under a pulse bias of −175 V and current density of 7.6 kA/cm2, the fabricated IMPATT diode exhibited gain between 19.3 and 50.1 GHz, with peak gain of 1.97 dB at ∼30.8 GHz. Temperature dependent characterization revealed that while the bias voltage required for operation at a given frequency changes significantly with temperature, consistent and stable performance can be achieved using a current source for biasing. For a fixed current density, both the avalanche frequency and device impedance remained relatively stable over a broad ambient temperature range. For use as a free-running oscillator, the minimum required Q for the external resonator was found to be less than 3.6, which is well within the range of what can be achieved in practice at these frequencies. Theoretical predictions of avalanche frequency were conducted and showed good agreement with the measured avalanche frequency, facilitating precise design of oscillators for applications. The fabricated IMPATT diodes demonstrate significant potential for high-power and high-efficiency signal generation from K-band to V-band across a wide temperature range.