Electric-field-induced optical hysteresis in single-layer WSe2

Abstract

We demonstrate that the exciton energy of a monolayer of tungsten diselenide on an SiO2/Si substrate can be tuned by an applied in-plane electric field for two samples with different dielectric capping materials. The exciton energy can be either red- or blue-shifted by up to 20 meV based on the polarity of the applied electric field. We argue that a piezoelectric effect creates a large internal electric field, which is either partially aligned or partially antialigned with the external electric field. Additionally, optical hysteresis is observed on cycling of the external electric field due to trapped charges.

Photoluminescence Switching Effect in a Two-Dimensional Atomic Crystal

“…The gate-voltage-dependent blue shift in this case was about 36 meV, which is the largest tunability of this line reported so far. 13,25 The exciton energy in this device shifted upward on both voltage polarities, but by different amounts, which may suggest different surface electric field magnitude. Although different ionic species accumulate at the channel top interface under different polarities (i.e., a cationic EDL forms at V SG > 0 V while an anionic EDL forms at V SG < 0 V), we do not anticipate a change in surface electric field magnitude because our previous experimental results using Hall effect measurements, transfer measurement, 23,26 and simulation results using finite element modeling 27 suggest that the cationic and anionic EDLs have very similar densities.…”

“…Low-dimensional semiconducting transition metal dichalcogenides (TMDs), with MX 2 stoichiometry, where M is a transition metal element from group VI (M = Mo, W) and X is a chalcogen (X = S, Se), have emerged as promising materials, offering complementary characteristics to graphene for electronics, photonics, and optoelectronics applications because of their unusual electrical and optical properties. − For example, these monolayers can be readily assembled together like “Lego blocks”, without large lattice mismatch effects, due to the interplane van der Waals forces, which offer a convenient and flexible approach to design various devices . In addition, TMDs can be integrated into photonic devices such as modulators, detectors, and optical microcavities. − Furthermore, the high mobility and the tunable bandgap of these materials enables them to be versatile components for electrical and optical circuits. − …”

Photoluminescence switching in a two-dimensional atomic crystal

“…The gate-voltage-dependent blueshift in this case was about 36 meV, which is the largest tunability of this line yet seen. 13,24 The exciton energy in this device shifted upward on both voltage polarities, by different amounts; a possible cause of the asymmetric behavior as a function of the applied voltage has been discussed in a previous paper. 13 The Schottky barrier heights between the metal and WSe 2 can be different in the same device despite using the same contact metal, due to Fermi level pinning or interfacial residue.…”

“…[8][9][10][11][12] Furthermore, the high mobility and the tunable bandgap of these materials enables them to be versatile components for electrical and optical circuits. [13][14][15][16] Here we report a photoluminescence switching effect based on monolayer WSe 2 transistors. The photoluminescence (PL) intensity of the WSe 2 element was tuned by applying vertical electric fields in a dual-gate geometry.…”

“…13 The Schottky barrier heights between the metal and WSe 2 can be different in the same device despite using the same contact metal, due to Fermi level pinning or interfacial residue. 13 1.61 Peak Energy (eV)…”