Design of GaN SBD with high cutoff frequency for THz mixer applications

This work firstly reports the high-frequency GaN planar Schottky barrier diodes (SBDs) for 220 GHz mixer applications, while conducting a systematic investigation into the design and optimization of device frequency performance through advanced device-level simulations. To enhance the cutoff frequency characteristics, device-level Sentaurus-TCAD simulation were employed to establish the quantitative relationship between critical structural parameters (N-GaN layer thickness and anode size) and key electrical parameters (series resistance R_s and zero-bias junction capacitance C_j0). Results reveal that the reduction of the N-GaN layer thickness combined with optimal anode size enables significant improvement in cutoff frequency, achieving theoretical values nearly 4 THz. Guided by these simulations, the device fabricated within current fabrication capabilities achieved a 31.55 Ω R and 2.1 fF C_j0 with a 50 nm N-GaN layer thickness and a 0.5 μm anode radius, producing a high cutoff frequency of 2.41 THz. Finally, the SBD fabricated based on simulation was embedded in a quartz based microstrip circuit for testing. The mixer exhibits good millimeter-wave performance with a conversion loss (CL) below 18 dB across 210–224 GHz and an input 1 dB compression point (P_in1dB) of 2 dBm at room temperature, confirming excellent linearity characteristics. This work establishes following advancements, including the development of a TCAD-based simulation framework for optimizing parasitic parameters and cutoff frequency in GaN SBDs, and the demonstration of high-frequency GaN SBDs’ potential in terahertz mixer systems, providing a novel methodology for advancing GaN technology in terahertz applications.