A TRANSFER LENGTH MODEL FOR CONTACT RESISTANCE OF 2-LAYER SYSTEMS WITH ARBITRARY INTERLAYER COUPLING UNDER THE CONTACTS

An improved analytical solution to the two-layer transmission line mod el for determining contact resistances to semiconductor layers is pres ented, In contrast to previously published two-layered analyses, the p resent solution is valid for arbitrary strength linear coupling betwee n the two conducting layers in the region under the contact, A compari son of limiting cases and a physical interpretation of the differences between predictions of this model and previous models are presented, The predicted resistance versus pad separation behavior obtained from the present model and from a two-layer model which assumed weak interl ayer coupling beneath the contacts are compared for identical physical structures, Experimental data for contact resistance measurements on a double-barrier resonant tunneling diode structure are presented, The measured data exhibit the nonlinear resistance versus pad spacing pre dicted by the model and show a dependence on current level which can h e modeled as a variation of the interlayer coupling strength, The valu es of the contact resistance, interlayer coupling resistance and sheet resistance extracted from the measured data using the present model a nd the weakly coupled model are presented and compared with independen tly measured and calculated parameters.