Two-Dimensional GeP-Based Broad-Band Optical Switches and Photodetectors

Germanium phosphide (GeP), a typical 2D group IV-V semiconductor, has attracted significant attention due to the advantages of higher thermodynamic stability than black phosphorus (BP), widely tunable bandgap, high carrier mobility, and in-plane anisotropy. However, its photonic and optoelectronic properties have not been extensively explored so far. Herein, large size and high-quality GeP single bulk crystal is successfully grown by flux method and stripped into 2D nanosheets with liquid phase exfoliation (LPE) and spin-coating methods. The broad-band photonic and optoelectronic properties of 2D GeP nanosheets are systematically investigated. First principles calculations are performed to verify its widely tunable bandgap from 0.43 eV for bulk to 1.58 eV for monolayer. The ultrafast carrier dynamic and non-linear optical responses are investigated by non-degenerated pump-probe and open-aperture Z-scan methods, and the results indicate that 2D GeP nanosheets can present excellent broad-band saturable absorption properties. Furthermore, the 2D GeP nanosheets-based broad-band saturable absorbers (SAs) and photodetectors are demonstrated. The results indicate that 2D GeP nanosheets can be used as excellent broad-band optical modulators and detectors, which will arouse a considerable interest in exploring novel group IV-V 2D materials for broad-band photonic and optoelectronic applications.