Optimization of off-state breakdown voltage in GaN high-electron-mobility transistors

Gallium nitride (GaN) technology is the next revolution in electronics as it offers a large bandgap (high critical electric field) and high electron mobility (2D electron gas) in one transistor design, surpassing silicon (Si), gallium arsenide (GaAs), and indium phosphide (InP) based technologies. High efficiency and high voltage operation of GaN high electron mobility transistors (HEMTs) provide significant performance and size advantages over the aforementioned devices. GaN HEMTs are normally-on devices, meaning that the devices do not shut down even though no gate voltage is applied, due to the 2D electron gas channel. In applications where safety and efficiency are in the forefront, normally-off devices are preferred. A simple way to obtain a normally-off GaN HEMT is to apply a negative gate voltage. A challenge of normally-off GaN HEMT is that the devices usually fail before the critical electric field is reached. Breakdown is caused by gate-leakage impact-ionization, drain-to-source punchthrough and vertical current leakage. Increasing the breakdown voltage would eliminate the damage in high voltage, high current applications and would extend the lifetime and operating bias conditions. The goal of this research is to design and simulate GaN-based power transistors in order to understand their different characteristics, such as voltage-current relations, using TCAD Sentaurus software. GaN HEMTs with different design strategies (i.e. doping concentration, layer thicknesses, layer contents) are simulated in order to understand their impact on off-state breakdown voltages. Based on the simulation results, different strategies to improve the off-state breakdown voltage are proposed.Ope