Small-Signal Modeling of Transitional Recess T-Gate N-Doped Cap AlGaN/GaN Fin-HEMTs for High Linearity and f max

This study presents a comprehensive numerical design and small-signal modeling of a 100-nm T-gate AlGaN/GaN Fin High Electron Mobility Transistor (HEMT) incorporating a Transitional Recess Gate (TRG) with recess depths ranging from 5 to 20 nm. The device structure, modeled using Silvaco TCAD, integrates an n-doped GaN cap layer to enhance carrier transport and electrostatic control. The numerical simulations were performed under varied gate and drain biases to analyze the impact of recess depth and cap doping on the intrinsic device parameters. The extracted small-signal parameters (gm, gd, Cgs, and Cgd) were obtained using the Dambrine method and validated across multiple bias conditions. The numerically derived small-signal model accurately reproduces the simulated S-parameter characteristics and provides physical insight into the bias-dependent transconductance and output conductance variations. Results show that the TRG configuration achieves improved transconductance linearity and an extended gate voltage swing (GVS), while maintaining stable high-frequency behavior with simulated fT and fmax values of 61 and 137 GHz, respectively.