High electron mobility field effect transistors were fabricated on heterostructures and their magnetoresistance was measured at up to with simultaneous modulation of the gate potential. Low and high magnetic field data were used to determine the electron mobility and concentration , respectively, in the gated part of the transistor channel. With these measurements we present a method to determine and under the gate of a transistor, which does not require knowledge of the transistor gate length, access resistance, threshold voltage, or capacitance. We discuss applications of this method for nanometer and ballistic transistors.
The contact resistance is defined here as the resistance of metallic source and drain electrodes. The access resistance is defined as the resistance of the ungated part of the channel, present in HEMTs and absent in Si MOSFETs.