Schottky Barrier Height Extraction in Ohmic Regime: Contacts on Fully Processed GeOI Substrates

Abstract

The problematics of contacts optimization on germanium metal-oxide-semiconductor field-effect transistors suffers from a gap between fundamental studies and the structures obtained after full processing. The contact properties of metals on Ge were so far mostly investigated on weakly n-doped samples under the pure thermionic emission regime. These experimental conditions are suitable for an accurate extraction; the measured Schottky barrier height (SBH) being usually large and linked to the interfacial current density by a relatively simple Arrhenius relationship. However, a device-oriented approach would consist in meeting the contact resistivity requirements in the ohmic regime for metallic contacts on a highly doped semiconductor (e.g., doped source and drain) through the choice of metal, interface preparation, and doping conditions. We hereby detail SBH extractions based on contact resistance measurements on highly n- and p-doped Ge, where the predominant tunnel current component results in ohmic behavior. We applied this methodology to our fully processed germanium-on-insulator (GeOI) samples with Ti-based contacts, yielding effective barriers of for electrons and for holes. The method provides a good physical understanding of the technological factors impacting the electrical properties, enabling to define paths toward ohmic-contact optimization in the context of device integration on GeOI.