Role of Seed Layer in Growing Atomically Flat TiTe ₂ /Sb ₂ Te ₃ Heterostructure Thin Films at the Wafer Scale

Abstract 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 TiTe ₂ /Sb ₂ Te ₃ . In this work, it is reported how to obtain highly textured TiTe ₂ /Sb ₂ Te ₃ 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 Sb ₂ Te ₃ 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 TiTe ₂ /Sb ₂ Te ₃ 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 TiTe ₂ slabs due to the lattice mismatch with the adjacent Sb ₂ Te ₃ 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.