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

Abstract

Understanding the remarkable excitonic effects and controlling the exciton binding energies in two-dimensional (2D) semiconductors are crucial in unlocking their full potential for use in future photonic and optoelectronic devices. Here, we demonstrate large excitonic effects and gate-tunable exciton binding energies in single-layer rhenium diselenide (ReSe2) on a back-gated graphene device. We used scanning tunneling spectroscopy and differential reflectance spectroscopy to measure the quasiparticle electronic and optical bandgap of single-layer ReSe2, respectively, yielding a large exciton binding energy of 520 meV. Further, we achieved continuous tuning of the electronic bandgap and exciton binding energy of monolayer ReSe2 by hundreds of milli–electron volts through electrostatic gating, attributed to tunable Coulomb interactions arising from the gate-controlled free carriers in graphene. Our findings open a new avenue for controlling the bandgap renormalization and exciton binding energies in 2D semiconductors for a wide range of technological applications.

Electrically controlled dielectric band gap engineering in a two-dimensional semiconductor

“…This shows that the amount by which the band gap can be tuned via the dielectric environment depends on the degree of internal screening in the 2D semiconductor itself. We note the band gap reduction found by Jiong et al [32], where a reduction of about 0.6 eV of the band gap was found when monolayer ReSe 2 was placed on doped graphene. We have calculated the averaged in-plane static polarizability of ReSe 2 to be 6.58 Å, corresponding to the orange dot in Fig.…”

“…It is clear that that the band gap reduction is stronger for 2D materials with weaker intrinsic screening suggesting that the band gap renormalization is determined by the relative change in screening provided by the graphene layer. The dashed lines are added as guides to the eye and the orange dot corresponds to previous experimental work [32] (see main text).…”

“…Subsequently, the concept of dielectric band gap engineering in 2D materials has been explored for both lateral [27,28] and vertical [29][30][31] heterostructure designs. In a recent work, Qiu et al [32] investigated the effect of dielectric screening on the quasiparticle band gap of a single layer of ReS 2 placed on top of a back-gated graphene sheet. They found that the band gap can be tuned between 2.15 and 1.93 eV when the gate voltage was varied between −63 and 45 V.…”

Control of electron-electron interaction in graphene by proximity screening

“…lectrostatic screening by conducting gates has previously been employed to suppress charge inhomogeneity in graphene [1][2][3] , alter its plasmon spectra 4,5 , and renormalize electronic spectra of monolayer semiconductors 6,7 . Elementary electrostatics tells us that the electron charge e placed at the distance d from a bulk conductor leads to a dipole potential evolving as 2ed 2 =r 3 at large in-plane distances r ) d, which is much weaker than the original, unscreened Coulomb potential, e=r.…”

Modulation of photocarrier relaxation dynamics in two-dimensional semiconductors

“…51 , © 2019 Springer Nature excitation 40,52,53 . Recently, it was measured by scanning tunneling spectroscopy that continuous, wide range (~200 meV) tuning of the electronic bandgap and exciton binding energy could be achieved in a ReSe 2 monolayer placed on a back-gated graphene device, which was attributed to the tuning of Coulomb interactions by gatecontrolled free carriers in graphene 54 . A decreased exciton binding energy could result in a reduction of the exciton oscillator strength.…”