Linear quantum-confined Stark effect and field tunable excitonic oscillator strength in bilayer WS₂

The reflection symmetry is broken while the inversion symmetry is restored in bilayer TMDs unlike monolayers¹. This results in anomalous field-dependent excitonic behavior in bilayer WS₂ compared with monolayers. First, we show a linear quantum-confined Stark effect of bilayer intra-layer excitons with a vertical electric field, contrary to a quadratic one for a monolayer. Second, we demonstrate a strong field-dependent tunability of the oscillator strength of the intra-layer exciton due to a partial interconversion from intra-layer to inter-layer character with an increase in the vertical field. Third, using a modified device structure, we also show an efficient modulation of the excitonic response by transferring the oscillator strength from exciton to trion via electrostatic doping. These demonstrations make bilayer WS₂ as an excellent candidate for the field tunable ultrathin electro-optical absorption modulator² at the exciton resonance. These observations can find applications in various domains ranging from novel photonic devices, optical modulators, optical computing to imaging, and on-chip reconfigurable compact devices for next-generation optoelectronics.
References:
1. Das, S., et al. Phys. Rev. B 2019, 99, 165411.
2. Scuri, G., et al. Phys. Rev. Lett. 2018, 120, 037402.