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Controlled p-type substitutional doping in large-area monolayer WSe2 crystals grown by chemical vapor deposition

Abstract

Tungsten diselenide (WSe2) is a particularly interesting 2D material due to its p-type conductivity. Here we report a systematic process to optimize crystal size by variation of multiple growth parameters resulting in hexagonal single crystals up to 160 μm wide. We then show that these large single crystals can be controllably in-situ doped with the acceptor Niobium (Nb). First principles calculations suggest that substitutional Nb doping of W would yield p-doping with no gap trap states. When used as the active layer of a field effect transistor (FET), doped crystals exhibit conventional p-type behavior, rather than the ambipolar behaviour seen in undoped WSe2 FETs. Nb-doped WSe2 FETs yield a maximum field effect mobility of 116 cm2 V-1 s-1, slightly higher than its undoped counterpart, with an on/off ratio of 106. Doping reduces the contact resistance of WSe2, reaching a minimum value of 0.55 kΩ-μm in WSe2 FETs. The areal density of holes in Nb-doped WSe2 is approximately double that of undoped WSe2, indicating that Nb doping is working as an effective acceptor. Doping concentration can be controlled over several orders of magnitudes, allowing it to control FET threshold voltage, reduce off-state FET leakage, and reduce the contact resistance of WSe2.

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Publication details

The article was received on 30 Aug 2018, accepted on 05 Nov 2018 and first published on 06 Nov 2018


Article type: Paper
DOI: 10.1039/C8NR07070A
Citation: Nanoscale, 2018, Accepted Manuscript
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    Controlled p-type substitutional doping in large-area monolayer WSe2 crystals grown by chemical vapor deposition

    S. K. Pandey, H. Alsalman, J. G. Azadani, N. Izquierdo, T. Low and S. A. Campbell, Nanoscale, 2018, Accepted Manuscript , DOI: 10.1039/C8NR07070A

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