26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Engineering strong mid-infrared absorption in graphene at low Fermi energy by coupling to nanostructured SiC

Not scheduled

1h 30m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral COMMAD - Optoelectronic and Microelectronic Materials and Devices Parallel sessions

Speaker

Hugh Paynter (Monash University)

Description

Graphene-based thermoradiative energy harvesting in the mid-infrared relies on maximising the photothermoelectric (PTE) response, which requires operation at a low Fermi energy ($E_F$). This creates a fundamental trade-off: conventional Fabry-Perot (FP) plasmonic resonances provide strong, spectrally selective absorption but require patterned graphene or a high $E_F$, reducing PTE efficiency. In contrast, graphene-coupled silicon carbide (SiC) cavities supporting magnetic polaritons (MPs) enable strong optical confinement at low $E_F$, albeit with broader spectral linewidths. Here, we demonstrate that sub-wavelength SiC trench cavities with a graphene overlayer support localised MP resonances within the SiC Reststrahlen band, providing an optical platform for efficient mid-infrared energy harvesting.

Finite-element (COMSOL) simulations guided the design and analysis of these hybrid modes, followed by fabrication of SiC trench arrays using electron-beam lithography. Fourier-transform infrared (FTIR) measurements of structures with and without graphene overlayer confirm the predicted MP resonances and their strong polarisation dependence. Transverse-magnetic excitation efficiently couples to highly confined gap modes, whereas transverse-electric illumination produces a negligible response. The measured resonance positions agree well with simulations, while remaining differences in linewidth and absorption strength are attributed to fabrication-induced structural non-uniformities, including graphene membrane deformation and interface inhomogeneities.

These results establish an experimentally validated optical platform for graphene thermoradiative devices. Ongoing work incorporates in-situ ion-gel gating to tune $E_F$, enabling active control of MP resonances and access to the higher-$E_F$ FP mode for direct comparison. Ultimately, these SiC nanostructures will be combined with graphene p-n junction devices, developed in parallel, to realise mid-infrared thermoradiative energy harvesting while optimising the trade-off between optical absorption and PTE performance.