Tunable excitons in multilayer graphene for on-chip infrared spectroscopy

AB-stacked bilayer graphene (BLG) and ABC-stacked trilayer graphene (TLG) host strong exciton resonances in mid-infrared to far-infrared spectral range. These excitons can be tuned by an out-of-plane electric field in a dual-gated field effect transistor device configuration. Firstly, I will show the basic exciton properties by using an FTIR-photocurrent spectroscopy technique, which feature a linewidth down to ~0.4 meV and a peak infrared absorption of more than 40%. Then I will demonstrate the concept of on-chip spectroscopy using these graphene devices as tunable infrared detectors. By electrically scanning the exciton resonance across the infrared spectral range, sharp absorption features corresponding to molecular fingerprints can be readily resolved in both the DC detection mode and AC-modulated detection mode. These on-chip spectrometers avoid conventional grating-based and FTIR spectrometers—opening up new routes for infrared detection and spectroscopy.