Ti₃C₂T_x MXene/Ge 2D/3D van der Waals heterostructures as highly efficient and fast response near-infrared photodetectors

Cost-effective and highly efficient near-infrared photodetectors are urgently demanded in many electronic and optoelectronic products for applications in both military and civil areas. Herein, by using a simple solution-based drop-casting technique, we fabricate a Ti₃C₂T_x MXene/Ge two-dimensional/three-dimensional van der Waals heterostructure, which can function well as a highly efficient near-infrared photodetector. When shined by 1550 nm light illumination, the heterostructure exhibits an apparent photovoltaic effect and can, thus, work as a self-driven near-infrared photodetector. A representative photodetector achieves a photocurrent responsivity of ∼314.3 mA W⁻¹ at zero bias voltage, which can be improved to as high as ∼642.6 mA W⁻¹ by applying a small reverse bias voltage of −1 V. In addition, other critical performance parameters such as current on/off ratio, specific detectivity, and response speed are estimated to be ∼430, ∼2.01 × 10¹¹ Jones, and 17.6/13.6 μs, respectively. The excellent device performance is comparable to that of many previously reported two-dimensional material/Ge heterostructure-based near-infrared photodetectors, which cannot be constructed using facile solution-based processes. This work provides a facile avenue for developing high-performance and low-cost near-infrared photodetectors, which will find important applications in future optoelectronic systems.