Thermally driven crossover from indirect toward direct bandgap in 2D Semiconductors: MoSe2 versus MoS2

Sefaattin Tongay, Jian Zhou, Can Ataca, Kelvin Lo, Tyler S. Matthews, Jingbo Li, Jeffrey C. Grossman, Junqiao Wu

Research output: Contribution to journalArticlepeer-review

869 Scopus citations

Abstract

Layered semiconductors based on transition-metal chalcogenides usually cross from indirect bandgap in the bulk limit over to direct bandgap in the quantum (2D) limit. Such a crossover can be achieved by peeling off a multilayer sample to a single layer. For exploration of physical behavior and device applications, it is much desired to reversibly modulate such crossover in a multilayer sample. Here we demonstrate that, in a few-layer sample where the indirect bandgap and direct bandgap are nearly degenerate, the temperature rise can effectively drive the system toward the 2D limit by thermally decoupling neighboring layers via interlayer thermal expansion. Such a situation is realized in few-layer MoSe2, which shows stark contrast from the well-explored MoS2 where the indirect and direct bandgaps are far from degenerate. Photoluminescence of few-layer MoSe2 is much enhanced with the temperature rise, much like the way that the photoluminescence is enhanced due to the bandgap crossover going from the bulk to the quantum limit, offering potential applications involving external modulation of optical properties in 2D semiconductors. The direct bandgap of MoSe2, identified at 1.55 eV, may also promise applications in energy conversion involving solar spectrum, as it is close to the optimal bandgap value of single-junction solar cells and photoelechemical devices.

Original languageEnglish (US)
Pages (from-to)5576-5580
Number of pages5
JournalNano Letters
Volume12
Issue number11
DOIs
StatePublished - Nov 14 2012
Externally publishedYes

Keywords

  • 2D-Semiconductors
  • MoS
  • MoSe
  • bandgap
  • photoluminescence
  • temperature dependence

ASJC Scopus subject areas

  • Bioengineering
  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanical Engineering

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