Study of AlGaN/GaN High-Electron-Mobility Transistors by Experiments and Simulations

Gallium nitride (GaN) is a semiconductor that possesses unique characteristics that make it advantageous for high power and high-frequency applications. There is an explosive evolution of nitride semiconductors in both optoelectronics and electronics in the last 30 years. However, some bottlenecks are blocking the pathway of GaN replacing the Si. This thesis addresses the experimental fabrication of Au-free ohmic contact. An Au-free ohmic contact on AlGaN/AlN/GaN heterostructures based on Ti/Al/Ta metal stack was realized using low annealing temperatures. The SiCl4 treatment at the contact region plays a critical role in improving the contact performance. The Au-free AlGaN/AlN/GaN HEMTs show a higher maximum drain current density and transconductance. This thesis also discussed the fabrication of normally-off AlGaN/GaN HEMTs. A normally-off AlGaN/GaN MIS-HEMTs is realized by BCl3/Cl2-based gate recessed dry etching. The threshold voltage is positively shifted by 6V while the gate current leakage is reduced by three orders. Finally, the theoretical discussion in improving the breakdown voltage of the GaN-based transistor is presented. The performances of the HEMT with gate grating field plate (GGFP), the HEMT with drain grating field plate (HEMT-D), and the HEMT with both gate and drain grating field plate (HEMT-GD) are analyzed based on the numerical calculations on Silvaco Atlas. The simulation results indicate the grating field plate at the gate or drain side can split the electric field peak, which further efficiently improves the breakdown voltage of the HEMT. Additionally, the optimization of the GGFP and DGFP design is discussed. The systematic study provides hints for future experimental realization.