Simulation and modeling of gallium nitride high-electron mobility transistors for non-alloyed ohmic contacts

The advantages of gallium nitride (GaN) high-electron mobility transistors, such as concentrated channel electron density, superior electron mobility, and high breakdown voltage, present an opportunity to replace silicon-based devices from modern power conversion systems in the near future. The development of low-resistance ohmic contacts in aluminium gallium nitride (AlGaN)-based GaN devices is crucial for predicting their performance. However, only limited studies have employed technology computer-aided design (TCAD) software to investigate contact resistance in GaN devices and to develop strategies for minimizing contact resistivity. Furthermore, the ohmic contact is able to be achieved only based on different configurations of metal stacks with annealing. This study, using Silvaco TCAD Atlas, first modeled contact resistance in a vertical structure and later extended the study to a lateral structure, which is more feasible for physical manufacturing. The investigation focused on various n++ regions with different doping levels beneath the metal to determine the best optimization for ohmic contact. The result revealed that reducing contact resistivity saturated (1 × 10−6 Ω/cm2) at a thickness of 18 nm for the heavily doped layer (≥ 1 × 1019 cm−3), beyond which no significant decrease in contact resistivity was observed for varying doping levels in n++ layers. This study demonstrates that including a heavily doped layer between the contact and semiconductor surfaces results in the ohmic behaviour emergence in metal contacts.