UNDERSTANDING THE SHEET RESISTANCE PARAMETER OF ALLOYED OHMIC CONTACTS USING A TRANSMISSION-LINE MODEL

The electrical characterization of alloyed ohmic contacts is commonly undertaken using a Transmission Line Model (TLM) network to model and experimentally determine two parameters-the specific contact resistanc e rho(c) and the sheet resistance R(sk) beneath a planar ohmic contact . This paper describes the use of a recently reported modification to the TLM network [the Tri-Layer Transmission Line Model (TLTLM)] to int erpret measurements of the sheet resistance parameter. The TLTLM netwo rk models the composite alloyed ohmic contact as three layers (metal l ayer, alloyed semiconductor layer and the unalloyed semiconductor laye r) and two interfaces between the three layers. By assigning appropria te parameters to the TLTLM network, it is possible to calculate a valu e for the sheet resistance R(sk) that has been experimentally derived using the standard TLM. The new TLTLM model predicts that values of R( sk) greater and less than R(sh) (the unmodified sheet resistance of th e epitaxial layer) are possible, in agreement with experimentally repo rted observations.