Graphene photodetectors with asymmetric device structures on silicon chips

Graphene is a promising material for developing high-speed and wide-wavelength-range photodetectors. However, since the polarities of the photovoltages at each graphene/electrode interface of two electrodes on both ends of the graphene are opposite, they are canceled out under macroscopic light irradiation to the photodetectors. In this study, we propose two graphene-based photodetectors with different asymmetric device structures that can suppress the cancelation of photovoltage at the interfaces of two electrodes. One of the photodetectors has a local shadow mask, where only one side of the graphene/electrode interface is shadowed by a metal mask. The other has electrodes of different shapes, where the contact area of graphene/electrode interface is different by using a comb-shaped electrode. We measured the position dependence of light detection by scanning the focused light around the graphene photodetectors, and asymmetric photovoltage mapping can be obtained owing to the asymmetric structure of the two photodetectors. Furthermore, we also demonstrated macroscopic light detection by the photodetectors in the visible, near-infrared, and mid-infrared regions by suppressing the photovoltage cancelation. These graphene-based photodetectors with asymmetric structures are suitable for use as macroscopic photodetectors in the wide band of visible, near-infrared and mid-infrared regions.