Microscopic understanding of ultrafast charge transfer in van-der-Waals heterostructures

Abstract

Van-der-Waals heterostructures show many intriguing phenomena including ultrafast charge separation following strong excitonic absorption in the visible spectral range. However, despite the enormous potential for future applications in the field of optoelectronics, the underlying microscopic mechanism remains controversial. Here we use time- and angle-resolved photoemission spectroscopy combined with microscopic many-particle theory to reveal the relevant microscopic charge transfer channels in epitaxial WS${}_2$/graphene heterostructures. We find that the timescale for efficient ultrafast charge separation in the material is determined by direct tunneling at those points in the Brillouin zone where WS${}_2$ and graphene bands cross, while the lifetime of the charge separated transient state is set by defect-assisted tunneling through localized sulphur vacanices. The subtle interplay of intrinsic and defect-related charge transfer channels revealed in the present work can be exploited for the design of highly efficient light harvesting and detecting devices.

37 pages, 16 figures

References in corpus (11)

• The electronic properties of graphene
• 2D materials and van der Waals heterostructures
• Observation of giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor
• k.p theory for two-dimensional transition metal dichalcogenide semiconductors
• Optical signature of symmetry variations and spin-valley coupling in atomically thin tungsten dichalcogenides
• Ultrafast transition between exciton phases in van der Waals heterostructures
• Interlayer coupling in commensurate and incommensurate bilayer structures of transition metal dichalcogenides
• Tunable Phases of Moiré Excitons in van der Waals Heterostructures
• Direct Determination of Band Gap Renormalization in Photo-Excited Monolayer MoS2
• Hybridized intervalley moiré excitons and flat bands in twisted WSe${}_2$ bilayers
• Theory of optically induced Förster Coupling in van der Waals coupled Heterostuctures

Cited by in corpus (9)

• Exciton optics, dynamics and transport in atomically thin semiconductors
• Picosecond energy transfer in a transition metal dichalcogenide-graphene heterostructure revealed by transient Raman spectroscopy
• Distance dependence of the energy transfer mechanism in WS${}_2$-graphene heterostructures
• Reduced absorption due to defect-localized interlayer excitons in transition metal dichalcogenide-graphene heterostructures
• Proximity-enhanced valley Zeeman splitting at the WS${}_2$/graphene interface
• k-resolved ultrafast light-induced band renormalization in monolayer WS${}_2$ on graphene
• Charge quenching at defect states in transition metal dichalcogenide-graphene van der Waals heterobilayers
• Designable exciton mixing through layer alignment in WS${}_2$-graphene heterostructures
• Ultrafast Charge Transfer Dynamics at the MoS${}_2$/Au Interface Observed via Optical Spectroscopy under Ambient Conditions