Phase-engineered low-resistance contacts for ultrathin MoS2 transistors

Abstract

Ultrathin molybdenum disulphide (MoS2) has emerged as an interesting layered semiconductor because of its finite energy bandgap and the absence of dangling bonds. However, metals deposited on the semiconducting 2H phase usually form high-resistance (0.7 kΩ μm-10 kΩ μm) contacts, leading to Schottky-limited transport. In this study, we demonstrate that the metallic 1T phase of MoS2 can be locally induced on semiconducting 2H phase nanosheets, thus decreasing contact resistances to 200-300 Ω μm at zero gate bias. Field-effect transistors (FETs) with 1T phase electrodes fabricated and tested in air exhibit mobility values of ~50 cm(2) V(-1) s(-1), subthreshold swing values below 100 mV per decade, on/off ratios of >10(7), drive currents approaching ~100 μA μm(-1), and excellent current saturation. The deposition of different metals has limited influence on the FET performance, suggesting that the 1T/2H interface controls carrier injection into the channel. An increased reproducibility of the electrical characteristics is also obtained with our strategy based on phase engineering of MoS2.

Low-Resistance 2D/2D Ohmic Contacts: A Universal Approach to High-Performance WSe2, MoS2, and MoSe2 Transistors

“…To date, various innovative strategies to reduce the contact resistance such as use of 3 graphene contacts 3,[18][19][20] and phase-engineering, 21,22 are still deficient as they do not offer true ohmic contact behavior or have insufficient thermal stability. Nearly barrier-free contacts to MoS 2 have been achieved by using graphene as contact electrodes because the Fermi level of graphene can be effectively tuned by a gate voltage to align with the conduction band minimum ( CBM ) of MoS 2 , which minimizes the Schottky barrier height (SBH).…”

“…21 However, a finite SBH is expected to arise for the electron (hole) channel, when the work function of the 1T metallic phase does not line up with the CBM (Valence band maximum; VBM) of the 2H phase. For instance, a large SBH is expected for the hole channel of MoS 2 FETs using this phase-engineering contact strategy because of the large offset between the work function of the 1T phase and the VBM of the 2H 4 phase.…”

Engineering the Structural and Electronic Phases of MoTe2 through W Substitution

“…The T d−phase is predicted to possess unique topological properties [6][7][8][9] which might lead to topologically protected non-dissipative transport channels 9 . Recently, it was argued that it is possible to locally induce phasetransformations in TMDs 3,10,11,14 , through chemical doping 12 , local heating 13 , or electric-field 14,15 to achieve ohmic contacts or to induce useful functionalities such as electronic phase-change memory elements 11 . The combination of semiconducting and topological elements based upon the same compound, might produce a new generation of high performance, low dissipation optoelectronic elements.…”

“…More precise control of the phase change might also be used to minimize the metal-semiconductor Schottky barrier by continuous evolution of the electronic band structure, in order to overcome current limits on optoelectronic performance 23 . In fact, recent work has reported contact phase engineering by laser processing 13 and chemical modification 12 .…”

Air Stable Doping and Intrinsic Mobility Enhancement in Monolayer Molybdenum Disulfide by Amorphous Titanium Suboxide Encapsulation

“…More recently, the use of phase engineered contacts 21 and chloride doping 22,23 were demonstrated on MoS2 with promising results. However, the stability of the phase engineered contacts under high-performance device operation is still unknown.…”