Semimetallic Graphene for Infrared Sensing

Both photothermal and photovoltaic infrared (IR) detectors employ sensing materials that have an optical band gap. Different from these conventional materials, graphene has a conical band structure that imposes zero band gap. In this study, using the semimetallic multilayer graphene, IR detection at room temperature is realized. The relatively high Seebeck coefficient, ranging from 40 to 60 μV/K, compared to that of the metal, and the large optical absorption in the mid-IR region, in the wavelength range of 7-17 μm, enable graphene to detect IR without an absorber, which is essential for most IR detectors because the band gap of the sensing materials is much larger than the energy of IR and the incident IR can be absorbed directly by the sensing material. Thus, the incident IR can be absorbed directly by the sensing material in our device. The developed detector with a SiN membrane shows high responsivity and detectivity, which are 140 V/W and 5 × 10⁸ cm·Hz^1/2/W at 5 Hz, respectively. In addition, the IR sensor shows a response time of 600 μs. In the room-temperature operation of the IR sensor array without cooling, our sensors detect IR emitted from a human body and track the movement. The availability of large-area graphene in current technology opens new applications for metallic two-dimensional materials and a possibility for scale-up.