title: Impact of Premetallization Surface Preparation on Nickel-based Ohmic Contacts to Germanium Telluride: An X-ray Photoelectron Spectroscopic Study.
abstract: Surfaces of polycrystalline α-GeTe films were studied by X-ray photoelectron spectroscopy (XPS) after different treatments in an effort to understand the effect of premetallization surface treatments on the resistance of Ni-based contacts to GeTe. UV-O3is often used to remove organic contaminants after lithography and prior to metallization; therefore, UV-O3treatment was used first for 10 min prior to ex situ treatments, which led to oxidation of both Ge and Te to GeOx(x < 2) and TeO2, respectively. Then the oxides were removed by deionized (DI) H2O, (NH4)2S, and HCl treatments. Additionally, in situ Ar+ion etching was used to clean the GeTe surface without prior UV-O3treatment. Ar+ion etching, H2O, and (NH4)2S treatments create a surface richer in Ge compared to the HCl treatment, after which the surface is Te-rich. However, (NH4)2S also oxidizes Ge and gradually etches the GeTe film. All treated surfaces showed poor stability upon prolonged exposure to air, revealing that even (NH4)2S does not passivate the GeTe surface. The refined transfer length method (RTLM) was used to measure the contact resistance (Rc) of as-deposited Ni-based contacts to GeTe as a function of premetallization surface preparation. HCl-treated samples had the highest Rc(0.036 ± 0.002 Ω·mm), which was more than twice that of the other surface treatments. This increase in Rcis attributed to formation of the Ni1.29Te phase at the Ni/GeTe interface due to an abundance of Te at the surface after HCl treatment. In general, treatments that resulted in Ge-rich surfaces offered lower Rc.
authors.affiliation: Department of Materials Science and Engineering and Materials Research Institute, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Haila M
authors.identifier: http://orcid.org/0000-0003-1288-3624
authors.initials: HM
authors.lastname: Aldosari
authors.affiliation: Department of Materials Science and Engineering and Materials Research Institute, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Hamed
authors.identifier: http://orcid.org/0000-0003-4004-1360
authors.initials: H
authors.lastname: Simchi
authors.affiliation: Department of Materials Science and Engineering and Materials Research Institute, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Zelong
authors.initials: Z
authors.lastname: Ding
authors.affiliation: Department of Materials Science and Engineering and Materials Research Institute, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Kayla A
authors.initials: KA
authors.lastname: Cooley
authors.affiliation: Department of Materials Science and Engineering and Materials Research Institute, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Shih-Ying
authors.initials: SY
authors.lastname: Yu
authors.affiliation: Department of Materials Science and Engineering and Materials Research Institute, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Suzanne E
authors.initials: SE
authors.lastname: Mohney
keywords: GeTe; X-ray photoelectron spectroscopy; contact; phase change material; surface