New low-cost graphene-based, light absorber increases the efficiency and performance of mid-IR photodetectors, photovoltaic devices and modulators

UCF researchers have invented a graphene-based optical detector device with an unprecedented light absorption value of 60 percent in the mid infrared spectral domain. Historically, graphene’s low optical absorbance (less than 2.5 percent) has made it unsuitable for many optoelectronic applications. With the UCF innovation, manufacturers can now greatly expand their use of graphene in optoelectronic devices such as ultrasensitive infrared photodetectors, sensors and modulators.

Various strategies use metals to try and amplify graphene’s light absorption. However, the metals—not the graphene—usually absorb most of the light. In comparison, the UCF device uses a cavity-coupled nanomesh graphene structure, which not only enables the graphene to detect light but also to respond to different wavelengths of light. Thus, it is dynamically tunable. Additionally, the device is low cost and easy to fabricate.

Technical Details

The invention comprises a nanostructured optical detector device and methods for fabricating it. In one example method, the device consists of a substrate base supporting a gold back reflector (mirror). Atop the reflector is a patterned monolayer graphene sheet sandwiched between dielectrics. The graphene contains circular holes laid out in a square lattice pattern with feature sizes larger than previous reported patterns, thus enabling easier fabrication. Manufacturers can use simple nanoimprinting lithography to produce the perforated pattern. An external voltage gate enables tuning of the Fermi energy and absorption of specific wavelengths, with optimized response in the 8-12 µm region.

The process preserves the material continuity for electronic conductivity (essential for optoelectronic devices), and enables direct plasmon excitation that is independent of the incident light polarization. A strong coupling between localized surface plasmon resonances on the nanomesh graphene and optical cavity modes enables a predicted maximum absorption of 60 percent and dynamic tunability of up to 2 µm. This closely corroborates with experimentally measured absorption of ~45 percent and tunability of up to 2 µm. Thus, the device delivers the highest absorption value and spectral shift ever observed in monolayer graphene.

Benefits

• Low cost (using nanoimprinting lithography) and easier fabrication
• Device architecture can induce considerable absorption for low mobility graphene—a significant improvement over devices that function only with high mobility graphene
• High efficiency light absorption in the 8-12 µm wavelength range
• Light absorption is dynamically tunable over a wide bandwidth

Applications

• Military use (such as multispectral night vision equipment, gas and chemical sensors)
• Multispectral imaging for space exploration
• Photodetectors
• Optical modulators