title: Black Phosphorus Transistors with Near Band Edge Contact Schottky Barrier.
abstract: Black phosphorus (BP) is a new class of 2D material which holds promise for next generation transistor applications owing to its intrinsically superior carrier mobility properties. Among other issues, achieving good ohmic contacts with low source-drain parasitic resistance in BP field-effect transistors (FET) remains a challenge. For the first time, we report a new contact technology that employs the use of high work function nickel (Ni) and thermal anneal to produce a metal alloy that effectively reduces the contact Schottky barrier height (ΦB) in a BP FET. When annealed at 300 °C, the Ni electrode was found to react with the underlying BP crystal and resulted in the formation of nickel-phosphide (Ni2P) alloy. This serves to de-pin the metal Fermi level close to the valence band edge and realizes a record low hole ΦB of merely ~12 meV. The ΦB at the valence band has also been shown to be thickness-dependent, wherein increasing BP multi-layers results in a smaller ΦB due to bandgap energy shrinkage. The integration of hafnium-dioxide high-k gate dielectric additionally enables a significantly improved subthreshold swing (SS ~ 200 mV/dec), surpassing previously reported BP FETs with conventional SiO2 gate dielectric (SS > 1 V/dec).
authors.affiliation: Silicon Nano Device Laboratory, Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117583 Singapore.|Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, 117546 Singapore.
authors.forename: Zhi-Peng
authors.initials: ZP
authors.lastname: Ling
authors.affiliation: NUSNNI-NanoCore, National University of Singapore, 117576 Singapore.
authors.forename: Soumya
authors.initials: S
authors.lastname: Sakar
authors.affiliation: NUSNNI-NanoCore, National University of Singapore, 117576 Singapore.
authors.forename: Sinu
authors.initials: S
authors.lastname: Mathew
authors.affiliation: Silicon Nano Device Laboratory, Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117583 Singapore.
authors.forename: Jun-Tao
authors.initials: JT
authors.lastname: Zhu
authors.affiliation: NUSNNI-NanoCore, National University of Singapore, 117576 Singapore.
authors.forename: K
authors.initials: K
authors.lastname: Gopinadhan
authors.affiliation: NUSNNI-NanoCore, National University of Singapore, 117576 Singapore.
authors.forename: T
authors.initials: T
authors.lastname: Venkatesan
authors.affiliation: Silicon Nano Device Laboratory, Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117583 Singapore.|Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, 117546 Singapore.
authors.forename: Kah-Wee
authors.initials: KW
authors.lastname: Ang