Role of Seed Layer in Growing Atomically Flat TiTe₂/Sb₂Te₃ Heterostructure Thin Films at the Wafer Scale

Chalcogenide phase-change materials (PCMs) are a leading candidate for advanced memory and computing applications. Epitaxial-like growth of chalcogenide thin films at the wafer scale is important to guarantee the homogeneity of the thin film but is challenging with magnetron sputtering, particularly for the growth of phase-change heterostructure (PCH), such as TiTe₂/Sb₂Te₃. In this work, it is reported how to obtain highly textured TiTe₂/Sb₂Te₃ heterostructure thin films with atomically sharp interfaces on standard silicon substrates. By combining atomic-scale characterization and ab initio simulations, the critical role of the Sb₂Te₃ seed layer is revealed in forming a continuous Si-Sb-Te mixed transition layer, which provides a wafer-scale flat surface for the subsequent epitaxial-like growth of TiTe₂/Sb₂Te₃ thin film. By gradually reducing the thickness of the seed layer, its critical limit is determined to be ≈2 nm. Non-negligible in-plane tensile strain is observed in the TiTe₂ slabs due to the lattice mismatch with the adjacent Sb₂Te₃ ones, suggesting that the chemical interaction across the structural gaps in the heterostructure is stronger than a pure van der Waals interaction. Finally, the potential choices of chalcogenides for atomically flat seed layers on standard silicon substrates are outlined, which can be used for wafer-scale synthesis of other high-quality PCM or PCH thin films.