Epitaxial growth of anisotropic SnSe on GaAs(001) via step-edge orientation control

Abstract

Epitaxial growth of orthorhombic SnSe on cubic substrates is challenging due to lattice symmetry mismatch and anisotropic bonding. Here, we demonstrate that epitaxial films with sharp interfaces can be achieved for layered SnSe grown directly on both on-axis and 4° miscut GaAs(001) substrates. The substrate miscut strongly influences the growth morphology, evolving from spirals on on-axis GaAs to a terraced structure on miscut GaAs. X-ray diffraction reveals that on-axis GaAs supports SnSe with two in-plane orientation variants, whereas the miscut substrate stabilizes a single orientation and introduces a small out-of-plane tilt. Accordingly, in-plane optical anisotropy is enhanced in the single-variant film compared to the double variant, as determined by cross-polar reflectance. High-resolution TEM shows that the SnSe/GaAs interface is atomically abrupt and incoherent, characteristic of quasi-van der Waals epitaxy. We find a pronounced tendency for the zigzag edges of SnSe to align parallel to step edges on both substrates, and we show that step skipping nucleation and layer growth on the miscut substrate lead to the additional tilt. These results establish direct SnSe/GaAs heteroepitaxy as a route to integrate anisotropic layered semiconductors with cubic platforms and show that miscut substrates provide additional control over in-plane anisotropy.