Hybrid metal-graphene terahertz optoelectronic system with tunable plasmonic resonance and method of fabrication
Inventors
Jadidi, Mohammad M. • SUSHKOV, ANDREI B. • Gaskill, David Kurt • Fuhrer, Michael • Drew, Howard Dennis • Murphy, Thomas E.
Assignees
Monash University • US Department of Navy • University of Maryland College Park
Publication Number
US-10672933-B2
Publication Date
2020-06-02
Expiration Date
2036-06-14
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Abstract
A new approach to graphene-enabled plasmonic resonant structures in the THz is demonstrated in a hybrid graphene-metal design in which the graphene acts as a gate-tunable inductor, and metal acts as a capacitive reservoir for charge accumulation. A large resonant absorption in graphene can be achieved using the metal-graphene plasmonic scheme, and the peak can approach 100% in an optimized device, ideal for graphene-based THz detectors. Using high mobility graphene (μ>50000 cm2V−1s−1) will allow anomalously high resonant THz transmission (near 100%) through ultra-subwavelength graphene-filled metallic apertures at a resonance frequency that is gate tunable. This metal-graphene plasmonic scheme enables near perfect tunable THz filter or modulator.
Core Innovation
This invention presents a new hybrid metal-graphene plasmonic resonant structure operating in the terahertz (THz) frequency range. The structure comprises a periodic array of narrow graphene channels formed in a metal layer patterned on a continuous graphene layer, where graphene acts as a gate-tunable inductive element and the metal serves as a capacitive reservoir for charge accumulation. This hybrid design enables strong coupling to THz radiation and achieves large resonant absorption in graphene, with peak absorption approaching 100% in optimized low-mobility graphene devices, which is ideal for graphene-based THz detectors.
The invention addresses the longstanding problem of increasing graphene's absorption in THz optoelectronic devices and enables tunable plasmonic resonances even when graphene is in electrical contact with a metal, a challenge due to conductive boundaries previously thought to prevent such resonances. It overcomes limitations of prior approaches, such as insufficient absorption, lack of tunability, and difficulties integrating electrical contacts and antenna coupling in graphene plasmonic structures. By exploiting the unique gate-tunable inductance of graphene combined with the capacitance of metal stripes, this invention establishes new plasmon resonance modes that facilitate the fabrication of practical, large area, tunable terahertz optoelectronic systems including photodetectors, filters, modulators, and oscillators.
Claims Coverage
The patent claims include one independent claim covering both a hybrid metal-graphene terahertz plasmon-enhanced optoelectronic structure and a method of its fabrication, encompassing multiple inventive features related to the device configuration, tuning mechanisms, and fabrication steps.
Hybrid metal-graphene plasmonic structure with tunable terahertz resonance
The structure comprises a graphene layer formed on a substrate with a patterned conductive metal layer forming a periodic array of conductive stripes separated by gaps that confine narrow graphene channels. An electrolyte layer envelops the conductive stripes and graphene channels. The device supports fully tunable plasmon resonances in the terahertz frequency range with the electromagnetic wave incident polarized perpendicular to the graphene channels, and the width of graphene channels is smaller than the wavelength.
Device geometric parameters for optimized plasmon resonance
The conductive stripes have widths exceeding those of the graphene channels which range from 100 nm to a few micrometers, with the ratio of the array period to the graphene channel width exceeding 10 and preferably around 20 to 23. The period of the conductive stripe array ranges from 1 μm to 9 μm.
Gate voltage and structural tuning of plasmonic resonance
The structure includes a gate terminal coupled to the electrolyte layer with a gate voltage source applied between the gate terminal and graphene layer. This allows control of the plasmon resonance frequency and absorption strength by tuning carrier density in the graphene channels and/or adjusting widths of conductive stripes and graphene channels.
Materials and substrate specifications
The conductive stripes are made of metal, such as gold, and are sandwiched between the graphene layer and electrolyte layer. The substrate is made of SiC (0001) material.
Method of fabrication of the plasmon-enhanced terahertz graphene-based optoelectronic structure
The method includes epitaxially forming a single graphene layer on a SiC substrate, forming a periodic array of metallic stripes on the graphene to define graphene channels confined in the gaps, applying an electrolyte layer atop the metallic stripes that contacts both metal and graphene, connecting a gate terminal to the electrolyte layer, and coupling a gate voltage source between the gate terminal and graphene layer. The geometry maintains the period-to-channel width ratio exceeding 10 and the carrier mobility ranges between 1,000 and 100,000 cm²/V·s.
The claims cover a novel hybrid metal-graphene structure with specific geometric and material parameters that enable fully tunable terahertz plasmon resonances controlled via gate voltage and structural modification, alongside a fabrication method realizing this structure on SiC substrates with electrolyte gating.
Stated Advantages
Enables near complete (approaching 100%) resonant absorption in graphene, ideal for high-performance terahertz photodetectors.
Achieves anomalously high resonant transmission approaching 100% in high-mobility graphene, beneficial for tunable terahertz filters and modulators.
Allows gate-tunable plasmon resonance frequency and absorption strength, enabling dynamic control of device operation.
Supports fabrication of large-area arrays of devices with improved absorption efficiency and tunability over a broad terahertz frequency range.
Documented Applications
Graphene-based terahertz photodetectors with enhanced absorption efficiency, high responsivity, and tunability.
Near perfect tunable terahertz filters and modulators exploiting high mobility graphene transmission properties.
Terahertz oscillators leveraging tunable plasmonic resonances in hybrid metal-graphene structures.
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