Very low-resistance Mo-based Ohmic contacts to GeTe

Abstract

Low-resistance and thermally stable Ohmic contacts are essential for radio frequency switches based on the unique phase change properties of GeTe. Herein, Mo-based Ohmic contacts to p-type GeTe are reported, including the effect of pre-metallization surface preparation and annealing on Mo/Ti/Pt/Au contacts. In-situ Ar+ plasma treatment resulted in a very low contact resistance of 0.004 ± 0.002 Ω mm (5 ± 3 × 10−9 Ω cm2), which could not be achieved using ex-situ surface treatments, highlighting the need for oxide-free interfaces to obtain very low contact resistance using Mo-based contacts. Experiments aimed at creating a more Ge- or Te-rich interface yielded higher contact resistances in both cases. The contact resistance increased for short-term annealing (30 min) above 200 °C and for long-term annealing (1 week) at 200 °C. No solid-state reaction between Mo and GeTe was observed using transmission electron microscopy with energy dispersive spectroscopy. However, Te migrated from GeTe after annealing at 200 °C for a week, resulting in the formation of platinum telluride within the contact.