Computational Modelling-Based Device Design for Improved mmWave Performance and Linearity of GaN HEMTs

In this work, a comprehensive, TCAD based design approach for mmWave (mmW) GaN HEMTs is presented. Unique trade-offs between epi-layer design and HEMT's mmW performance are discussed. Effect of surface states on cut off frequency is modeled and presented. We have found that carrier trapping by the donor type interface states causes RF performance drift at high drain fields, which particularly leads to the non-linear behavior of mmW HEMTs at high drain bias. Moreover, we have observed that channel electrostatics, barrier layer, and UID GaN channel design govern the linearity and scaling behavior of such GaN HEMTs. To improve channel electrostatics, which improves the linearity and cut-off frequency, a partially recessed barrier under the gate is studied. A relative study of AlN/GaN HEMT and AlGaN/GaN HEMTs is performed to investigate the nonlinearity behavior. In addition, the dependence of cut-off frequency on contact resistance and lateral scaling is studied for partially-recessed barrier and conventional design for both AlN and AlGaN barrier types. The mmW performance is found to be a strong function of barrier design in the gate and recess regions. Unique design trends and physical behavior was observed for AlN and AlGaN barriers, which signifies that design guidelines derived for one epi-stack can't be deployed to the other.