Thermal stability of low-resistance Au Ohmic contacts to GeTe

Abstract

Low-resistance Ohmic contacts for phase change materials (PCMs) such as GeTe are required for devices such as radio frequency switches. The contacts must also exhibit good thermal stability since the PCM is switched by heating. In this work, Au Ohmic contacts to GeTe have been examined, including the effect of pre-metallization surface preparation and annealing on the resistance of the contacts. Although some form of pre-metallization surface treatment must be performed after photolithography to produce contacts with low resistance, the contact resistance (Rc) and specific contact resistance (ρc) were insensitive to the pre-metallization surface treatment chosen, whether in-situ Ar+ plasma treatment was used, or UV-O3 treatments followed by immersion in deionized H2O, (NH4)2S, or HCl. In all cases, Rc was 0.007±0.001Ω·mm and ρc was 1.2–1.3×10−8Ω·cm2. Thermal stability was also investigated at 250, 300, and 350°C for 30min. The contact resistance increased as annealing temperature increased, and changes in the contacts were observed using field emission scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy. No solid-state reaction occurred between Au and GeTe, even at 350°C. Rather, the increase in resistance could be attributed to slit-like defects that appeared and grew in the Au layer, through which sublimation of Te occurred.