Comparison of passivation layers for AlGaN/GaN high electron mobility transistors

Abstract

AlGaN/GaN high electron mobility transistors require surface passivation layers to reduce the effects of surface traps between the gate and drain contacts. These traps lead to the creation of a virtual gate and the associated collapse of drain current under rf conditions. The authors have investigated three different materials for passivation layers, namely thin (7.5 nm) Al2O3 and HfO2 deposited with an atomic layer deposition system and conventional, thick (200 nm) plasma enhanced chemically vapor deposited SiNX. The latter is found to be the most effective in reducing drain current loss during gate lag measurements in both single and double pulse mode, but also reduces fT and fMAX through additional parasitic capacitance.