Enhancing Spin Photocurrent in Scalable Monolayer MoS₂ Plasmonic Phototransistors Using Chiral Metasurfaces

The broken inversion symmetry and valley-selection rule due to the different spin orientations within the split valence band of each K(K’) valleys in monolayer MoS₂ (1L-MoS₂) justifies their potential applications for spintronic devices, valley-sensitive optoelectronic devices and quantum-based information processing. However, the ability to distinguish the degree of freedom between left/right circularly polarized (L/RCP) spin photocurrent is still a challenge due to the low photoresponsivity and lack of polarization sensitivity in 1L-MoS₂ at room temperature conditions. To counter these concerns, we propose a spin photocurrent sensitive plasmonic phototransistors with wafer-scaled 1L-MoS₂ integrated with gold chiral metasurfaces upon a hafnium nitride substrate. The geometry and handedness of the chiral metasurfaces were designed via finite-difference time-domain (FDTD) methods and the calculated absorption spectra signified that the left/right handed orientation of the gold chiral plasmonic metasurfaces dictates the selective absorption enhancement of L/RCP light (or vice versa) upon the 1L-MoS₂ surface. An additional plasmonic hafnium nitride material (deposited via RF-magnetron sputtering at 800°C) was introduced as a gate electrode with excellent metallic properties and strong local surface plasmon resonance attributes within the visible spectrum [1,2]. The inclusion of hafnium nitride plays a crucial role in amplifying the light-matter interaction upon the 1L-MoS₂ layer, where a 4-fold enhancement factor was observed from the photocurrent measurements (in comparison to pristine p⁺-Si substrate). Spin photocurrent measurements at different wavelengths showed up to 30.02% change at 660 nm (on-resonance with MoS₂) and less than 10% change at 450 nm and 550 nm (off-resonance). Overall, these promising results reveal a clear distinguishable approach to manipulate and tailor the L/RCP spin photocurrent at room temperature conditions. Ultimately, we will discuss the potential applications of ultrathin plasmonic phototransistors with high spin-selective photoresponse.

Reference
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