Ambipolar MoS2 Transistors by Nanoscale Tailoring of Schottky Barrier Using Oxygen Plasma Functionalization

Filippo Giannazzo; Gabriele Fisichella; Giuseppe Greco; Salvatore Di Franco; Ioannis Deretzis; Antonino La Magna; Corrado Bongiorno; Giuseppe Nicotra; Corrado Spinella; Michelangelo Scopelliti; Bruno Pignataro; Simonpietro Agnello; Fabrizio Roccaforte

doi:10.1021/acsami.7b04919

Ambipolar MoS₂ Transistors by Nanoscale Tailoring of Schottky Barrier Using Oxygen Plasma Functionalization

ACS Appl Mater Interfaces. 2017 Jul 12;9(27):23164-23174. doi: 10.1021/acsami.7b04919. Epub 2017 Jun 26.

Authors

Filippo Giannazzo¹, Gabriele Fisichella¹, Giuseppe Greco¹, Salvatore Di Franco¹, Ioannis Deretzis¹, Antonino La Magna¹, Corrado Bongiorno¹, Giuseppe Nicotra¹, Corrado Spinella¹, Michelangelo Scopelliti^{2

3

4}, Bruno Pignataro^{2

3}, Simonpietro Agnello^{2

3}, Fabrizio Roccaforte¹

Affiliations

¹ CNR-IMM , Strada VIII, 5, 95121 Catania, Italy.
² Dipartimento di Fisica e Chimica (DiFC), Università degli Studi di Palermo , Viale delle Scienze, Ed. 17, 90128 Palermo, Italy.
³ Aten Center, Università di Palermo , Ed. 18 V.le delle Scienze, Parco d'Orleans II, 90128 Palermo, Italy.
⁴ Consorzio Interuniversitario di Ricerca in Chimica dei Metalli nei Sistemi Biologici (C.I.R.C.M.S.B.) , 1, Piazza Umberto I, 70121 Bari, Italy.

PMID: 28603968
DOI: 10.1021/acsami.7b04919

Abstract

One of the main challenges to exploit molybdenum disulfide (MoS₂) potentialities for the next-generation complementary metal oxide semiconductor (CMOS) technology is the realization of p-type or ambipolar field-effect transistors (FETs). Hole transport in MoS₂ FETs is typically hampered by the high Schottky barrier height (SBH) for holes at source/drain contacts, due to the Fermi level pinning close to the conduction band. In this work, we show that the SBH of multilayer MoS₂ surface can be tailored at nanoscale using soft O₂ plasma treatments. The morphological, chemical, and electrical modifications of MoS₂ surface under different plasma conditions were investigated by several microscopic and spectroscopic characterization techniques, including X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), conductive AFM (CAFM), aberration-corrected scanning transmission electron microscopy (STEM), and electron energy loss spectroscopy (EELS). Nanoscale current-voltage mapping by CAFM showed that the SBH maps can be conveniently tuned starting from a narrow SBH distribution (from 0.2 to 0.3 eV) in the case of pristine MoS₂ to a broader distribution (from 0.2 to 0.8 eV) after 600 s O₂ plasma treatment, which allows both electron and hole injection. This lateral inhomogeneity in the electrical properties was associated with variations of the incorporated oxygen concentration in the MoS₂ multilayer surface, as shown by STEM/EELS analyses and confirmed by ab initio density functional theory (DFT) calculations. Back-gated multilayer MoS₂ FETs, fabricated by self-aligned deposition of source/drain contacts in the O₂ plasma functionalized areas, exhibit ambipolar current transport with on/off current ratio I_on/I_off ≈ 10³ and field-effect mobilities of 11.5 and 7.2 cm² V^-1 s^-1 for electrons and holes, respectively. The electrical behavior of these novel ambipolar devices is discussed in terms of the peculiar current injection mechanisms in the O₂ plasma functionalized MoS₂ surface.

Keywords: DFT calculations; MoS2; Schottky barrier; ambipolar transistors; atomic resolution STEM; conductive atomic force microscopy.