Near-lossless 2D semiconductor phase modulators using hybrid tungsten oxyselenide/graphene electrodes

Researchers from Nanyang Technological University, University of Chicago, University of Wisconsin, Chungnam National University, National Institute for Materials Science, MIT and Singapore University of technology and design have developed hybrid tungsten oxyselenide/graphene electrodes that enable near-lossless optical phase modulation in two-dimensional semiconductor devices. The work targets a long-standing trade-off in integrated photonics, where improving modulation efficiency typically increases optical loss, especially for graphene-based designs at telecommunication wavelengths.

In this approach, monolayer WSe₂ is converted by UV–ozone treatment into tungsten oxyselenide (TOS), which acts as a strong p‑type dopant for graphene. Heavy p‑doping shifts graphene’s Fermi level such that its absorption around 1550 nm is strongly suppressed, while its conductivity is enhanced, allowing graphene to function as a transparent, low-resistance top electrode in the near‑infrared.

Schematic of the fabricated device structure, consisting of a capacitor stack (monolayer WS2/hBN/graphene/TOS) integrated onto a SiN microring resonator. Right top: Side-view schematic of the device, highlighting electrical contacts with the bottom WS2 layer and top graphene electrode, connected independently to gold electrodes for voltage biasing. Right bottom: Optical image of the actual device. Image from: Light: Science & ApplicationsIn this approach, monolayer WSe₂ is converted by UV–ozone treatment into tungsten oxyselenide (TOS), which acts as a strong p‑type dopant for graphene. Heavy p‑doping shifts graphene’s Fermi level such that its absorption around 1550 nm is strongly suppressed, while its conductivity is enhanced, allowing graphene to function as a transparent, low-resistance top electrode in the near‑infrared.

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