RF Transmission Line Method for Wide-Bandgap Heterostructures

We propose a high-frequency extension of the transmission line model method that allows for independent extraction of open-surface sheet resistance of a semiconductor layer and that under metallization. The method is applied for the characterization of an AlGaN/GaN heterostructure with a high ( ~40%) Al content with and without a top dielectric layer. In both cases, the sheet resistance under the metal is approximately 30% smaller than that under the open surface. This reduction is attributed to the surface charge compensation by the top metal.