Interface State Artefact in Long Gate-Length AlGaN/GaN HEMTs

Dispersion in capacitance and conductance measurements in AlGaN/GaN high-electron mobility transistors is typically interpreted as resulting from interface states. Measurements on varying gate-length devices and a model of an interface-trap-free device are used to demonstrate that the distributed-resistance-induced dispersion is significant for 1-MHz measurements if the gate length exceeds ~10 μm. Hence, interface state density measurements using the conductance technique need to use shorter gate-length devices in order to avoid this artefact.