A computational analysis of the impact of thin undoped channels in surface-related current collapse of AlGaN/GaN HEMTs

This study provides an insight into the impact of thin purely undoped GaN channel thickness (t_ch) on surface-related trapping effects in AlGaN/GaN high electron mobility transistors. Our TCAD study suggests that in cases where parasitic gate leakage is the driving trapping mechanism that promotes the injection of electrons from the Schottky gate contact into surface states, this effect can be alleviated by reducing t_ch of the undoped GaN channel. We show that by decreasing t_ch from 130 to 10 nm, devices exhibit a reduction in gate-related current collapse under the specific class-B RF operating bias conditions as a consequence of a substantial decrease in the off-state gate leakage with reducing t_ch. Large-signal simulations revealed an increase by 3 W mm⁻¹ and about 12% output power and power-added efficiency due to the decrease of gate-related collapse. This work, for the first time, highlights the role of a proper purely undoped GaN t_ch selection to alleviate gate-related surface trapping in the design of GaN-based microwave power amplifiers.