2D MXene Electrode-Enabled High-Performance Broadband Photodetector Based on a CVD-Grown 2D Bi₂Se₃ Ultrathin Film on Silicon

Topological insulators, such as Bi 2 Se 3, show great promise in the quest for materials with exceptional optoelectronic capabilities in the visible to mid-infrared range due to their unique Dirac-like surface states with a small bulk band gap and broadband light absorption. Here, we report a low-temperature chemical vapor deposition (CVD) of a highly crystalline Bi 2 Se 3 ultrathin film on a Si substrate, and the Si/Bi 2 Se 3 heterojunction shows a very broadband absorption in the range of 300–2000 nm. A Si/Bi 2 Se 3 heterostructure photodetector with two-dimensional MXene electrodes was constructed for the first time. The MXene electrode-enabled photodetector exhibits a truly broadband light detection in the range of 300–1550 nm and a very fast response of a few microseconds (rise time of 19.7 μs and fall time of 35.2 μs). The device demonstrates a high responsivity of 6.96 A/W, a high detectivity of 6.31 × 10 12 Jones, a large linear dynamic range of 92.93 dB, and an excellent on/off ratio of 1.9 × 10 4 at 808 nm. It also exhibits self-biased (0 V) photodetection with a reasonably high responsivity of 24.7 mA/W and excellent detectivity of 4.16 × 10 11 Jones under illumination. The highest responsivity and detectivity of the device are found to be 7.56 A/W and 6.85 × 10 12 Jones, respectively, at 980 nm. The exceptional crystallinity of the Bi 2 Se 3 film characterized by superior crystal quality and low defect density at the Si/Bi 2 Se 3 interface, along with the presence of a strong built-in electric field, contributes to the observed superior performance of the heterojunction photodetectors. Additionally, the synthesis and functionalization of Ti 3 C 2 T x MXene allow for the preparation of high-quality electrodes by a simple spin-casting process at a low cost. The van der Waals MXene–Bi 2 Se 3 interface effectively reduces the dark current and enhances the collection of photon-excited carriers due to the low density of chemical disorders and negligible defects.