Strain-Engineered Photodetector for Silicon Photonics

Researchers discovered a new way to engineer opto­electronic devices by stretching a two-dimensional material on top of a silicon photonic platform. Using this method, the researchers around Volker Sorger, George Washington Uni­versity, demonstrated for the first time that a 2D material wrapped around a nanoscale silicon photonic waveguide creates a novel photo­detector that can operate with high efficiency at the tech­nology-critical wavelength of 1550 nanometers. Such new photo­detection can advance future communi­cations and computer systems, especially in emerging areas such as machine learning and arti­ficial neural networks.

Artistic representation of strain engineered 2D photodetector on silicon photonic circuit. (Source: M. Miscuglio)

The ever-increasing data demand of modern societies requires a more efficient conversion of data signals in the optical domain, from fiber optic internet to elec­tronic devices, like a smartphone or laptop. This conversion process from optical to electrical signals is performed by a photo­detector, a critical building block in optical networks. 2D materials have scientific and techno­logically relevant proper­ties for photo­detectors. Because of their strong optical absorp­tion, designing a 2D material-based photo­detector would enable an improved photo-conversion, and hence more efficient data trans­mission and telecommuni­cations. However, 2D semi­conducting materials, such as those from the family of transition metal dichalcogenides, have, so far, been unable to operate effi­ciently at tele­communication wavelengths because of their large optical bandgap and low absorption.

Strainoptronics provides a solution to this short­coming and adds an engi­neering tool for researchers to modify the electrical and optical properties of 2D materials, and thus the pioneered 2D material-based photo­detectors. Realizing the potential of strain­optronics, the researchers stretched an ultrathin layer of molybdenum telluride, a 2D material semi­conductor, on top of a silicon photonic waveguide to assemble a novel photo­detector. They then used their newly created strain­optronics control knob to alter its physical properties to shrink the electronic bandgap, allowing the device to operate at near infrared wavelengths, namely at the tele­communication (C-band) relevant wavelength around 1550 nm.

The researchers noted one interesting aspect of their discovery: the amount of strain these semiconductor 2D materials can bear is signifi­cantly higher when compared to bulk materials for a given amount of strain. They also note these novel 2D material-based photo­detectors are 1,000 times more sensitive compared to other photo­detectors using graphene. Photo­detectors capable of such extreme sensitivity are useful not only for data communi­cation appli­cations but also for medical sensing and possibly even quantum information systems.

“We not only found a new way to engineer a photo­detector, but also discovered a novel design metho­dology for opto­electronic devices, which we termed strain­optronics. These devices bear unique properties for optical data communi­cation and for emerging photonic arti­ficial neural networks used in machine learning and AI“, Sorger said. „Interes­tingly, unlike bulk materials, two-dimen­sional materials are parti­cularly promising candi­dates for strain engineering because they can withstand larger amounts of strain before rupture. In the near future, we want to apply strain dynamically to many other two-dimen­sional materials in the hopes of finding endless possi­bilities to optimize photonic devices“, postdoc Rishi Maiti added. (Source: GWU)

Reference: R. Maiti et al.: Strain-engineered high-responsivity MoTe2 photodetector for silicon photonic integrated circuits, Nat. Phot., online 22 June 2020; DOI: 10.1038/s41566-020-0647-4

Link: Orthogonal-Physics-Enabled-Nanophotonics Lab, Dept. of Electrical and Computer Engineering, George Washington University, Washington DC, USA

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