Wedding cake growth and ultraviolet performance of β-GeSe2 nanosheets†

As an important layered material, two-dimensional (2D) GeSe₂ has recently attracted interest owing to its direct wide bandgap and potential applications in ultraviolet (UV) detection. Herein, we utilized GeTe as a Ge precursor for the growth of β-GeSe₂ nanosheets on mica via chemical vapor deposition. By optimizing the growth time and temperature, high-quality β-GeSe₂ nanosheets with various vertical stacking configurations were achieved. Detailed investigation shows the formation of wedding-cake-like β-GeSe₂ with terraced structures originating from the high supersaturation of precursors. With increasing temperature and growth time, supersaturation was enhanced and β-GeSe₂ nanosheets formed a wedding cake structure. Moreover, the thickness of β-GeSe₂ nanosheets with flat surfaces is down to 9.2 nm. The intensity of Raman vibration peaks varies across positions with different thicknesses on the β-GeSe₂ nanosheet. With decreasing thickness of the terraced structure of GeSe₂ nanosheets, the A_g Raman vibration peak becomes weaker because of the reduction in the number of scattering centers. Furthermore, angle-resolved polarization Raman spectroscopy was conducted at room temperature. Additionally, the optical properties of β-GeSe₂ nanosheets demonstrated that the β-GeSe₂ nanosheets with a pyramid stacked structure exhibited a direct broadband gap of 2.72 eV. The results indicate that the β-GeSe₂ nanosheets are potential material for ultraviolet photodetection and polarized optoelectronic devices.