Synthesis of low-symmetry 2D Ge(1-x)SnxSe2 alloy flakes with anisotropic optical response and birefringence.

Low-symmetry two-dimensional (2D) materials with unique in-plane anisotropy can promote both fundamental science and practical applications in optics, optoelectronics, electronics, and polarization detection. As a member of 2D materials, doping/alloying material systems have gained great attention owing to the tunable bandgap and special properties. However, the in-plane anisotropic optical and electrical properties of these 2D alloy materials have rarely been reported. In this work, low-symmetry 2D Ge(1-x)SnxSe2 (x = 0-1.0) alloy flakes have been synthesized by chemical vapor deposition (CVD) with a bandgap varying from 1.55 eV (GeSe2, x = 0) to 1.90 eV (SnSe2, x = 1.0). Angle-resolved polarized Raman spectroscopy (ARPRS) is used to confirm the in-plane vibrational anisotropy, and azimuth-dependent reflectance difference microscopy (ADRDM) is applied to visualize the in-plane optical anisotropy. Polarization-dependent transmission spectroscopy (PDTS) is carried out to reflect the in-plane absorptional anisotropy and linear dichroism, and birefringence characteristics are also found in the subsequent studies. All of the results indicate the unique in-plane optical anisotropy and birefringence characteristics of the 2D Ge(1-x)SnxSe2 alloy flakes, providing new opportunities for polarization-controlled devices, optical wave plates, and polarizers.