Electromechanically control the optoelectronic properties of 2D semiconductors

Abstract

2D materials have exhibited rich distinct properties, which can cover a broad optical spectral range with strong light-matter interactions. The properties of 2D materials are very sensitive to the local environment so their properties are easily controlled by the external field. In this thesis, I will mainly discuss how the electrical and mechanical methods can control the interlayer coupling of 2D materials and modulate their optoelectronic properties. I will show two different material systems that can be controlled by external approaches. In the first part, the electric field is utilized to modulate the optical absorption of black Phosphorus (bP) thin film. The modulation peaks of the bP flakes are related to the subband transitions which also show strong layer dependence. With 9 nm bP flake, the transitions with the same and different band indexes have been observed and more than 5 percent modulation of absorption has been demonstrated in the thin film device. This strong modulation of the bP absorption leads to optoelectronic applications such as integrated mid-infrared photodetectors and modulators. For the second part, we achieve the photodetection at the mid-IR region with the responsivity of 2.5 mA/W. Also, the 9 dB/mm modulation depth has been demonstrated in the straight waveguide device and more than 40 dB/mm are predicted based on the simulation of the ideal fabricated sample. In the last part, I will show that the piezoelectric field of the surface acoustic wave can strongly interact with the bilayer transition metal dichalcogenides (TMDCs) so that the exciton can be spatially manipulated by the propagating acoustic waves with the propagation length exceeding 20 µm. Both temperature and power-dependence of the SAW devices have been characterized that we clearly resolve the transition from exciton localization to transport regime. Due to the strong acoustic modulation, more than 2 µm transport length has been achieved even at room temperature. This acoustic approach in general can also be applied to other physical systems such as Moire heterobilayers (MoSe2/WSe2) by considering the vertical dipole moment of the Moire exciton.