Interstitial Mo-Assisted Photovoltaic Effect in Multilayer MoSe2 Phototransistors

Sunkook Kim; Jesse Maassen; Jiyoul Lee; Seung Min Kim; Gyuchull Han; Junyeon Kwon; Seongin Hong; Jozeph Park; Na Liu; Yun Chang Park; Inturu Omkaram; Jong-Soo Rhyee; Young Ki Hong; Youngki Yoon

doi:10.1002/adma.201705542

Interstitial Mo-Assisted Photovoltaic Effect in Multilayer MoSe₂ Phototransistors

Adv Mater. 2018 Mar;30(12):e1705542. doi: 10.1002/adma.201705542. Epub 2018 Jan 25.

Authors

Affiliations

¹ Multi-Functional Nano/Bio Electronics Laboratory, Sungkyunkwan University, Gyeonggi, 16419, South Korea.
² Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, B3H 4R2, Canada.
³ Department of Graphic Arts Information Engineering, Pukyong National University, Busan, 608-739, South Korea.
⁴ Institute of Advanced Composite Materials, Korea Institute of Science and Technology, Jeonbuk, 565-905, South Korea.
⁵ Department of Electrical and Computer Engineering and Waterloo Institute for Nanotechnology (WIN), University of Waterloo, Waterloo, ON, N2L 3G1, Canada.
⁶ Measurement & Analysis Team, National Nanofab Center, Daejeon, 34141, South Korea.
⁷ Department of Applied Physics, Kyung Hee University, Gyeonggi, 17104, South Korea.

PMID: 29369423
DOI: 10.1002/adma.201705542

Abstract

Thin-film transistors (TFTs) based on multilayer molybdenum diselenide (MoSe₂ ) synthesized by modified atmospheric pressure chemical vapor deposition (APCVD) exhibit outstanding photoresponsivity (103.1 A W^-1 ), while it is generally believed that optical response of multilayer transition metal dichalcogenides (TMDs) is significantly limited due to their indirect bandgap and inefficient photoexcitation process. Here, the fundamental origin of such a high photoresponsivity in the synthesized multilayer MoSe₂ TFTs is sought. A unique structural characteristic of the APCVD-grown MoSe₂ is observed, in which interstitial Mo atoms exist between basal planes, unlike usual 2H phase TMDs. Density functional theory calculations and photoinduced transfer characteristics reveal that such interstitial Mo atoms form photoreactive electronic states in the bandgap. Models indicate that huge photoamplification is attributed to trapped holes in subgap states, resulting in a significant photovoltaic effect. In this study, the fundamental origin of high responsivity with synthetic MoSe₂ phototransistors is identified, suggesting a novel route to high-performance, multifunctional 2D material devices for future wearable sensor applications.

Keywords: 2D materials; MoSe2; interstitial effects; phototransistors; photovoltaics.