Thickness modulation of incline-grown Bi₂O₂Se for the construction of high-performance phototransistors

Newly emerging two-dimensional (2D) Bi2O2Se has received intense research interest due to its unique band structure and ultrafast optical properties. However, the device performance of Bi2O2Se-based photodetectors is far from the expectation because of the undesirable contact issues of the contaminates from the fabrication process or the high Schottky barrier caused by the large work function mismatch. In this work, highly efficient photodetection based on an "all-Bi2O2Se" device geometry has been demonstrated. By controlling the growth conditions, Bi2O2Se flakes with thicknesses of 8-15 nm (thin) and >40 nm (thick) are obtained. The thin one is a typical n-type semiconductor, while the thick one shows the degenerated n-type behavior with a higher Fermi level. Two thick flakes are adopted as 2D contacts for the absorption layer of thin flake, leading to the upward movement of the thin flake band structures. By tailoring the Schottky barrier frame at the interface junction, the high barriers are eliminated, which boost the transport and collection of photo-generated electrons. The photodetector demonstrates strong photoresponse to visible and near-infrared light. High photoresponsivity and specific detectivity of 3.34 x 10(4) A/W and 6.61 x 10(13) Jones, respectively, are achieved under the 640 nm light illumination.