High bandwidth and responsivity mid-infrared graphene photodetector based on a modified metal-dielectric-graphene...

In this paper, a novel graphene-based mid-infrared photoconductive photodetector is designed that is composed of nanophotodetectors in series and parallel forming an array. The whole structure utilizes a single "unpatterned" graphene layer in a modified metal-dielectric-graphene (MDG) architecture that is composed of a conventional MDG structure combined with additional nanoelectrodes for photocurrent guiding and absorption enhancement. Finite difference time domain and finite element methods are utilized to obtain optical and electrostatic characteristics of the photodetector. Specifically, responsivity, quantum efficiency, dark current, bandwidth, noise equivalent power (NEP), and specific detectivity (D^*) are extracted by employing realistic graphene as well as graphene-metal characteristics. For an optimized device, maximum absorption efficiency is as much as 70% at a wavelength of λ=6.77  μm; however, the peak absorption wavelength can be effectively tuned between λ=6-7  μm. It is shown that increasing the drain-source voltage enhances the responsivity and bandwidth with a side effect of increasing the dark current. Responsivity of the 2×2 photodetector is R_A=0.63  AW^-1 for V =0.5  V with I =350  μA, NEP=16.91  pW/√Hz, and D^*=1.53×10⁵ Jones.