Valley relaxation of resident electrons and holes in a monolayer semiconductor: Dependence on carrier density and the role of substrate-induced disorder

Jing Li, M. Goryca, K. Yumigeta, H. Li, S. Tongay, S. A. Crooker

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Using time-resolved optical Kerr rotation, we measure the low-temperature valley dynamics of resident electrons and holes in exfoliated WSe2 monolayers as a systematic function of carrier density. In an effort to reconcile the many disparate timescales of carrier valley dynamics in monolayer semiconductors reported to date, we directly compare the doping-dependent valley relaxation in two electrostatically gated WSe2 monolayers having different dielectric environments. In a fully encapsulated structure (hBN/WSe2/hBN, where hBN is hexagonal boron nitride), valley relaxation is found to be monoexponential. The valley relaxation time τv is quite long (∼10μs) at low carrier densities, but decreases rapidly to less than 100 ns at high electron or hole densities â‰2×1012cm-2. In contrast, in a partially encapsulated WSe2 monolayer placed directly on silicon dioxide (hBN/WSe2/SiO2), carrier valley relaxation is multiexponential at low carrier densities. The difference is attributed to environmental disorder from the SiO2 substrate. Unexpectedly, very small out-of-plane magnetic fields can increase τv, especially in the hBN/WSe2/SiO2 structure, suggesting that localized states induced by disorder can play an important role in depolarizing spins and mediating the valley relaxation of resident carriers in monolayer transition-metal dichalcogenide semiconductors.

Original languageEnglish (US)
Article number044001
JournalPhysical Review Materials
Volume5
Issue number4
DOIs
StatePublished - Apr 2021
Externally publishedYes

ASJC Scopus subject areas

  • Materials Science(all)
  • Physics and Astronomy (miscellaneous)

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