An Analytical Model for Alloyed Ohmic Contacts Using a Trilayer Transmission Line Model

Abstract

This paper describes a Transmission Line Model approach to the modeling and analysis of alloyed planar ohmic contacts. It briefly reviews the standard Transmission Line Model (TLM) commonly used to characterize a planar ohmic contact. It is shown that in the case of a typical Au-Ge-Ni alloyed ohmic contact, a more realistic model based on the TLM should take into account the presence of the alloyed layer at the metalsemiconductor interface. In this paper, such a model is described. It is based on three layers and the two interfaces between them, thus forming a 'hi-Layer Transmission Line Model (TLTLM). Analytical expressions are derived for the contact resistance Rc and the contact end resistance Re of this structure, together with a current division factor, f. Values for the contact parameters of this TLTLM model are inferred from experimentally reported values of Rc and Re for two types of contact. Using the analytical outcomes of the TLTLM, it is shown that the experimental results obtained using a standard TLM can have considerable discrepancies.