A comparison of the tri-layer transmission line model and a finite element model for ohmic contact analysis

Alloyed ohmic contacts to GaAs consist of separate alloyed and unalloyed layers beneath the contact metal layer. (A similar situation is metal to silicide to silicon contacts.) Thus there are three distinct layers separated by two interfaces, each layer having a different resistivity and each interface having a different specific contact resistance. Such a multiple layer contact makes the modeling and calculation of specific contact resistance (ρc) a non-trivial problem. The standard Transmission Line Model (TLM) allows for only two layers and one interface and hence reports a composite sheet resistance Rskand ρcrather than two of each. In this paper results from the analytical Tri-Layer Transmission Line Model (TLTLM) and a two-dimensional finite-element-model are compared when both models are used to calculate the contact resistance of a Tri-layer ohmic contact using a standard TLM test pattern.