Anomalous photoresponse in the deep-ultraviolet due to resonant excitonic effects in oxygen plasma treated few-layer graphene

Graphene holds great promise for novel optoelectronic devices due its exceptional optical properties. Here we report an anomalous photoresponse due to resonant excitonic effects in oxygen functionalized epitaxial graphene (EG) with gain exceeding 104 in the deep-ultraviolet (DUV) region. The method used to introduce the oxygen adatoms is via mild oxygen plasma treatment. Upon oxygen adsorption, spectral weight transfer occurs and a photoresponse emerges. The photoresponse in the oxygen plasma treated EG (OPTEG) is attributed to the enhancement of the resonant exciton in the DUV and suppression of optical conductivity below it, as evidenced in our spectroscopic ellipsometry measurements. Our result shows that the OPTEG produces large photoconductive gain, high selectivity, and detectivity in excess of 1012 Jones in the DUV spectral range and can be harnessed to fabricate tunable graphene-based high-gain DUV photodetectors.