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Tailoring synthesis of high-vacancy MoSe2-x monolayer crystals

by Masoud Mahjouri-Samani, Liangbo Liang, Akinola Oyedele, et al.

Atomically resolved Z-contrast scanning transmission electron microscopy images show MoSe2 crystals synthesized with high (~20%) and low (<1%) Se-vacancy concentrations. Associated device-transport characteristics exhibit p- and n-type carrier behavior, r

Atomically resolved Z-contrast scanning transmission electron microscopy images show MoSe2-x crystals synthesized with high (~20%) and low (<1%) Se-vacancy concentrations. Associated device-transport characteristics exhibit p- and n-type carrier behavior, respectively.

Abstract 

Defect engineering has been a critical step in controlling the transport characteristics of electronic devices, and the ability to create, tune, and annihilate defects is essential to enable the range of next-generation devices. Whereas defect formation has been well-demonstrated in three-dimensional semiconductors, similar exploration of the heterogeneity in atomically thin two-dimensional semiconductors and the link between their atomic structures, defects, and properties has not yet been extensively studied. Here, we demonstrate the growth of MoSe2−x  single crystals with selenium (Se) vacancies far beyond intrinsic levels, up to ∼ 20%, that exhibit a remarkable transition in electrical transport properties from n- to p-type character with increasing Se vacancy concentration. A new defect-activated phonon band at ∼ 250 cm−1  appears, and the A1g  Raman characteristic mode at 240 cm−1  softens toward ∼ 230 cm−1  which serves as a fingerprint of vacancy concentration in the crystals. We show that post-selenization using pulsed laser evaporated Se atoms can repair Se-vacant sites to nearly recover the properties of the pristine crystals. First-principles calculations reveal the underlying mechanisms for the corresponding vacancy induced electrical and optical transitions.

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Publication Citation

Nano Letters 2016 pp 5213-5220
DOI: 10.1021/acs.nanolett.6b02263

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