Highly In-Plane Optical and Electrical Anisotropy of 2D Germanium Arsenide

Anisotropic 2D materials exhibit unique optical, electrical, and thermoelectric properties that open up possibilities for diverse angle-dependent devices. However, the explored anisotropic 2D materials are very limited and the methods to identify the crystal orientations and to study the in-plane anisotropy are in the initial stage. Here azimuth-dependent reflectance difference microscopy (ADRDM), angle-resolved Raman spectra, and electrical transport measurements are used to systematically characterize the influence of the anisotropic structure on in-plane optical and electrical anisotropy of 2D GeAs, a novel group IV-V semiconductor. It is proved that ADRDM offers a way to quickly identify the crystal orientations and also to directly characterize the in-plane optical anisotropy of layered GeAs. The anisotropic electrical transport behavior of few-layer GeAs field-effect transistors is further measured and the anisotropic ratio of the mobility is as high as 4.6, which is higher than the other 2D anisotropic materials such as black phosphorus. The dependence of the Raman intensity anisotropy on the sample thickness, excitation wavelength, and polarization configuration is investigated both experimentally and theoretically. These data will be useful for designing new high-performance devices and the results suggest a general methodology for characterizing the in-plane anisotropy of low-symmetry 2D materials.