Formation of Twin-Free Single Phase β-In₂Se₃ Layers via Selenium Diffusion into InP(111)B Substrate

Indium selenide, In₂Se₃, has recently attracted growing interest due to its remarkable properties, including room temperature ferroelectricity, outstanding photoresponsivity, and exotic in-plane ferroelectricity, which open up new regimes for next generation electronics. In₂Se₃ also provides the important advantage of tuning the electrical properties of ultrathin layers with an external electrical and magnetic field, making it a potential platform to study novel two-dimensional physics. Yet, In₂Se₃ has many different polymorphs, and it has been challenging to synthesize a single phase material, especially using scalable growth methods, as needed for technological applications. We recently reported the growth of twin-free ultrathin layers of In₂Se₃ prepared by a diffusion driven molecular beam epitaxy approach, and twin-free Bi₂Se₃ layers grown on these unique virtual substrates. In this paper, we use aberration-corrected scanning transmission electron microscopy to characterize the microstructure of these materials. We emphasize features of the In₂Se₃ layer and In₂Se₃/InP interface which provide evidence for understanding the growth mechanism that leads to the twin-free and single phase In₂Se₃. We also show that this In₂Se₃ layer provides an ideal substrate for growth of twin-free Bi₂Se₃ with a nearly defect-free interface. This approach for growing high-quality twin-free single phase two-dimensional crystals using InP substrates is likely to be applicable to other technologically important materials.