Hybrid graphene/silicon Schottky photodiode with intrinsic gating effect

We propose a hybrid device consisting of a graphene/silicon (Gr/Si) Schottky diode in parallel with a Gr/SiO₂/Si capacitor for high-performance photodetection. The device, fabricated by transfer of commercial graphene on low-doped n-type Si substrate, achieves a photoresponse as high as 3 AW^-1 and a normalized detectivity higher than 3.5×10¹² cm Hz^1/2 W^-1 in the visible range. It exhibits a photocurrent exceeding the forward current because photo-generated minority carriers, accumulated at Si/SiO₂ interface of the Gr/SiO₂/Si capacitor, diffuse to the Gr/Si junction. We show that the same mechanism, when due to thermally generated carriers, although usually neglected or disregarded, causes the increased leakage often measured in Gr/Si heterojunctions. We perform extensive I-V and C-V characterization at different temperatures and we measure a zero-bias Schottky barrier height of 0.52 eV at room temperature, as well as an effective Richardson constant A^∗∗ = 4×10^-5 A cm^-2 K^-2 and an ideality factor n∼3.6, explained by a thin (<1 nm) oxide layer at the Gr/Si interface.