title: Effective Schottky Barrier Height Lowering of Metal/n-Ge with a TiO2/GeO2Interlayer Stack.
abstract: A perfect ohmic contact formation technique for low-resistance source/drain (S/D) contact of germanium (Ge) n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) is developed. A metal-interlayer-semiconductor (M-I-S) structure with an ultrathin TiO2/GeO2interlayer stack is introduced into the contact scheme to alleviate Fermi-level pinning (FLP), and reduce the electron Schottky barrier height (SBH). The TiO2interlayer can alleviate FLP by preventing formation of metal-induced gap states (MIGS) with its very low tunneling resistance and series resistance and can provide very small electron energy barrier at the metal/TiO2interface. The GeO2layer can induce further alleviation of FLP by reducing interface state density (Dit) on Ge which is one of main causes of FLP. Moreover, the proposed TiO2/GeO2stack can minimize interface dipole formation which induces the SBH increase. The M-I-S structure incorporating the TiO2/GeO2interlayer stack achieves a perfect ohmic characteristic, which has proved unattainable with a single interlayer. FLP can be perfectly alleviated, and the SBH of the metal/n-Ge can be tremendously reduced. The proposed structure (Ti/TiO2/GeO2/n-Ge) exhibits 0.193 eV of effective electron SBH which achieves 0.36 eV of SBH reduction from that of the Ti/n-Ge structure. The proposed M-I-S structure can be suggested as a promising S/D contact technique for nanoscale Ge n-channel transistors to overcome the large electron SBH problem caused by severe FLP.
authors.forename: Gwang-Sik
authors.identifier: http://orcid.org/0000-0002-9329-4006
authors.initials: GS
authors.lastname: Kim
authors.forename: Sun-Woo
authors.identifier: http://orcid.org/0000-0002-2041-1451
authors.initials: SW
authors.lastname: Kim
authors.forename: Seung-Hwan
authors.identifier: http://orcid.org/0000-0002-5899-2853
authors.initials: SH
authors.lastname: Kim
authors.forename: June
authors.initials: J
authors.lastname: Park
authors.affiliation: School of Electrical Engineering, Korea Advanced Institute of Science and Technology , Daejeon 34141, Korea.
authors.forename: Yujin
authors.initials: Y
authors.lastname: Seo
authors.affiliation: School of Electrical Engineering, Korea Advanced Institute of Science and Technology , Daejeon 34141, Korea.
authors.forename: Byung Jin
authors.identifier: http://orcid.org/0000-0003-3000-5403
authors.initials: BJ
authors.lastname: Cho
authors.affiliation: School of Electrical and Computer Engineering, University of Seoul , Seoul 02504, Korea.
authors.forename: Changhwan
authors.identifier: http://orcid.org/0000-0001-6057-3773
authors.initials: C
authors.lastname: Shin
authors.forename: Joon Hyung
authors.initials: JH
authors.lastname: Shim
authors.forename: Hyun-Yong
authors.identifier: http://orcid.org/0000-0001-9446-5981
authors.initials: HY
authors.lastname: Yu
keywords: Fermi-level unpinning; Schottky barrier height; contact resistance; germanium; germanium dioxide; plasma oxidation; titanium dioxide