Comparison of Methods for Accurate Characterization of Interface Traps in GaN MOS-HFET Devices

Reliability of dielectrics is a critical concern in GaN metal-oxide-semiconductor-heterojunction-field-effect transistor (MOS-HFET) devices for use in high-voltage power and RF applications. Accurate characterization of interface traps is essential toward developing an understanding of the reliability issues associated with this system and to evaluate the effectiveness of different dielectrics proposed for use in the gate-stack or the passivation of the access regions. Using small-signal equivalent circuit models and TCAD simulations, it is found that conductance and capacitance methods for trap density estimation potentially have severely constrained detection limits and can probe only shallow traps. In contrast, a pulsed-IV method, used along with UV irradiation, can accurately detect a wide range of trap densities over the entire wide bandgap. The effectiveness of this method is also experimentally demonstrated using an AlGaN/GaN MOS-HFET device with HfAlO gate dielectric.