Unveiling Defect-Mediated Carrier Dynamics in Monolayer Semiconductors by Spatiotemporal Microwave Imaging
arXiv:2003.01817 · doi:10.1073/pnas.2004106117
Abstract
The optoelectronic properties of atomically thin transition-metal dichalcogenides are strongly correlated with the presence of defects in the materials, which are not necessarily detrimental for certain applications. For instance, defects can lead to an enhanced photoconduction, a complicated process involving charge generation and recombination in the time domain and carrier transport in the spatial domain. Here, we report the simultaneous spatial and temporal photoconductivity imaging in two types of WS2 monolayers by laser-illuminated microwave impedance microscopy. The diffusion length and carrier lifetime were directly extracted from the spatial profile and temporal relaxation of microwave signals respectively. Time-resolved experiments indicate that the critical process for photo-excited carriers is the escape of holes from trap states, which prolongs the apparent lifetime of mobile electrons in the conduction band. As a result, counterintuitively, the photoconductivity is stronger in CVD samples than exfoliated monolayers with a lower defect density. Our work reveals the intrinsic time and length scales of electrical response to photo-excitation in van der Waals materials, which is essential for their applications in novel optoelectronic devices.
arXiv comment21 pages, 4 figures
References in corpus (23)
- Atomically thin MoS2: A new direct-gap semiconductor
- Control of valley polarization in monolayer MoS2 by optical helicity
- Two-Dimensional Material Nanophotonics
- Extraordinary room-temperature photoluminescence in WS2 monolayers
- Optoelectronics with electrically tunable PN diodes in a monolayer dichalcogenide
- Optical Generation of Excitonic Valley Coherence in Monolayer WSe2
- Mechanisms of photoconductivity in atomically thin MoS2
- Intrinsic Exciton Linewidth in Monolayer Transition Metal Dichalcogenides
- Exciton Radiative Lifetime in Transition Metal Dichalcogenide Monolayers
- Electron and Hole Mobilities in Single-Layer WSe2
- Impact of Grain Boundaries on Efficiency and Stability of Organic-Inorganic Trihalide Perovskites
- Ultrafast and spatially resolved studies of charge carriers in atomically-thin molybdenum disulfide
- Statistical Study of Deep Sub-Micron Dual-Gated Field-Effect Transistors on Monolayer CVD Molybdenum Disulfide Films
- Elucidating the photoresponse of ultrathin MoS2 field-effect transistors by scanning photocurrent microscopy
- Control of Exciton Valley Coherence in Transition Metal Dichalcogenide Monolayers
- Microsecond Valley Lifetime of Defect-Bound Excitons in Monolayer WSe
- Observation of Ultrafast Free Carrier Dynamics in Single Layer MoS
- Exciton diffusion in WSe2 monolayers embedded in a van der Waals heterostructure
- Modeling of a Cantilever-Based Near-Field Scanning Microwave Microscope
- Effect of Point Defects on the Optical and Transport Properties of MoS2 and WS2
- Energy-resolved Photoconductivity Mapping in a Monolayer-bilayer WSe2 Lateral Heterostructure
- Tailoring Semiconductor Lateral Multi-junctions for Giant Photoconductivity Enhancement
- Optically Coupled Methods for Microwave Impedance Microscopy
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- Nanoscale Conductivity Imaging of Correlated Electronic States in WSe2/WS2 Moiré Superlattices
- Superior Photo-carrier Diffusion Dynamics in Organic-inorganic Hybrid Perovskites Revealed by Spatiotemporal Conductivity Imaging
- Johnson-noise-limited cancellation-free microwave impedance microscopy with monolithic silicon cantilever probes
- Electron dynamics in a 2D nanobubble: A two-level system based on spatial density
- Phonon-mediated exciton capture in Mo-based transition metal dichalcogenides