Mid-Infrared Pyroresistive Graphene Detector on LiNbO3

Mid-infrared (mid-IR) photo-detection has been recently growing in importance because of its multiple applications, including vibrational spectroscopy and thermal imaging. We propose and demonstrate a novel pyro-resistive photo-detection platform that combines a ferroelectric substrate (a z-cut LiNbO3 crystal) and a graphene layer transferred on top of its surface with electrical connections. Upon strong light absorption in the LiNbO3 substrate and the subsequent temperature increase, via the pyroelectric effect, polarization (bound) charges form at the crystal surface. These causes doping into graphene which in turn changes its carrier density and conductivity. In this way, by monitoring the graphene electrical resistance one can measure the incident optical power. . Detectivities of about 10^5 cm sqrt(Hz)/W in the 6 to 10 microns wavelength region are demonstrated.We explain the underlying physical mechanism of the pyro-resistive photo-detection and propose a model that reproduces accurately the experimental results. We also show that up to two orders of magnitude larger detectivity can be achieved by optimising the geometry and operating in vacuum, thus opening the path to a new class of mid-IR photo-detectors that can challenge classical HgCdTe devices, especially in real applications where cooling is to be avoided and low cost is crucial.