On-Wafer Characterization of K-Band to V-Band GaN IMPATT Diodes

High-gain GaN impact-ionization avalanche transit-time (IMPATT) diodes have been fabricated and experimentally characterized. The devices feature a “Hi-Lo” design; temperature dependent reverse I-V measurement verified impact ionization avalanche as the dominant breakdown mechanism. IMPATT operation was confirmed, with reflection gain observed between 20 GHz and 45 GHz using pulsed bias conditions of -177 V and current density of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$7.5 \text{kA} / \text{cm}^{2}$</tex>. A peak reflection gain of 1.4 dB was observed around 30 GHz. On-wafer S-parameter measurements revealed large negative differential resistance of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$-803 \Omega$</tex>, comparable to state of the art Si IMPATT diodes. The RF output power density is projected to be 42.1 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{kW} / \text{cm}^{2}$</tex> at 35 GHz. The short-pulse on-wafer S-parameter-based measurement technique used here facilitates direct extraction of device impedance, providing insights into the optimal impedance matching of the peripheral resonant circuit and the appropriate operating frequency. These devices are promising for high-power, high-efficiency K-band to V-band signal generation.