Giant gate-tunable bandgap renormalization and excitonic effects in a 2-D semiconductor

phys.org | 10/10/2018 | Staff
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Investigating the remarkable excitonic effects in two-dimensional (2-D) semiconductors and controlling their exciton binding energies can unlock the full potential of 2-D materials for future applications in photonic and optoelectronic devices. In a recent study, Zhizhan Qiu and colleagues at the interdisciplinary departments of chemistry, engineering, advanced 2-D materials, physics and materials science in Singapore, Japan and the U.S. demonstrated large excitonic effects and gate-tunable exciton binding energies in single-layer rhenium diselenide (ReSe2) on a back-gated graphene device. They used scanning tunneling spectroscopy (STS) and differential reflectance spectroscopy to measure the quasiparticle (QP) electronic and optical bandgap (Eopt) of single-layer ReSe2 to yield a large exciton binding energy of 520 meV.

The scientists achieved continuous tuning of the electronic bandgap and exciton binding energy of monolayer ReSe2 by hundreds of milli-electron volts via electrostatic gating. Qiu et al. credited the phenomenon to tunable Coulomb interactions arising from the gate-controlled free carriers in graphene. The new findings are now published on Science Advances and will open a new avenue to control bandgap renormalization and exciton binding energies in 2-D semiconductors for a variety of technical applications.

Semiconductors - Bandgap - Renormalization - Shifts - Qualities

Atomically thin two-dimensional (2-D) semiconductors usually display large bandgap renormalization (shifts in physical qualities) and extraordinary excitonic effects due to quantum confinement and reduced dielectric screening. Light-matter interactions in these systems are governed by enhanced excitonic effects, which physicists have studied to develop exciton-based devices at room temperature. A unique feature of 2-D semiconductors is their unprecedented tunability relative to both electric and optical properties due to doping and environmental screening.

Researchers can engineer theoretically predicted and experimentally demonstrated Coulomb interactions in 2-D semiconductors to tune the quasiparticle bandgap (Eg) and exciton binding energies (Eb) of samples, with methods such as chemical doping, electrostatic gating and engineering environmental screening. Among the reported techniques, electrostatic gating offers additional advantages...
(Excerpt) Read more at: phys.org
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