title: Self-Limiting Oxides on WSe2 as Controlled Surface Acceptors and Low-Resistance Hole Contacts.
abstract: Transition metal oxides show much promise as effective p-type contacts and dopants in electronics based on transition metal dichalcogenides. Here we report that atomically thin films of under-stoichiometric tungsten oxides (WOx with x < 3) grown on tungsten diselenide (WSe2) can be used as both controlled charge transfer dopants and low-barrier contacts for p-type WSe2 transistors. Exposure of atomically thin WSe2 transistors to ozone (O3) at 100 °C results in self-limiting oxidation of the WSe2 surfaces to conducting WOx films. WOx-covered WSe2 is highly hole-doped due to surface electron transfer from the underlying WSe2 to the high electron affinity WOx. The dopant concentration can be reduced by suppressing the electron affinity of WOx by air exposure, but exposure to O3 at room temperature leads to the recovery of the electron affinity. Hence, surface transfer doping with WOx is virtually controllable. Transistors based on WSe2 covered with WOx show only p-type conductions with orders of magnitude better on-current, on/off current ratio, and carrier mobility than without WOx, suggesting that the surface WOx serves as a p-type contact with a low hole Schottky barrier. Our findings point to a simple and effective strategy for creating p-type devices based on two-dimensional transition metal dichalcogenides with controlled dopant concentrations.
authors.affiliation: WPI Center for Materials Nanoarchitechtonics (WPI-MANA), National Institute for Materials Science , Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Mahito
authors.initials: M
authors.lastname: Yamamoto
authors.affiliation: WPI Center for Materials Nanoarchitechtonics (WPI-MANA), National Institute for Materials Science , Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Shu
authors.initials: S
authors.lastname: Nakaharai
authors.affiliation: Department of Chemistry, Graduate School of Science and Engineering, Saitama University , Saitama 338-8570, Japan.
authors.forename: Keiji
authors.initials: K
authors.lastname: Ueno
authors.affiliation: WPI Center for Materials Nanoarchitechtonics (WPI-MANA), National Institute for Materials Science , Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Tsukagoshi
keywords: Layered transition metal dichalcogenides; field effect transistors; hole injection; p-type doping; tungsten diselenide; tungsten oxides