A two-layer magneto-TLM contact resistance model: application to modulation-doped FET structures

The resistance for a two-layer structure with planar contacts is derived, with both the contacts and the region between the contacts modeled as transmission lines. Magnetic field effects are included, yielding additional information on mobilities and carrier concentrations. The theory can be fitted to the usual resistance-versus-contact-separation data as a function of magnetic field strength. Fitted parameters include mobilities and carrier concentrations in each layer, both under the contact and in the bulk material between the contacts, as well as specific contact resistivities for the contact barriers. Experimental results are obtained for an AlGaAs/InGaAs modulation-doped FET structure