The (GeTe) m (Sb2Te3) n alloy (Ge-Sb-Te-GST) is a key phase change material (PCM), widely studied for its cutting-edge technological applications. It is a prominent material for phase change memories, and, very recently, has attracted new interest as the most advanced emerging non-volatile memory technology for neuromorphic applications [1-2]. The ability of growing high-quality epitaxial GST represents a key-point to tailor the material properties, such as a large programming window [3], improved cycling endurance and faster crystallization [4]. Depending on n and m, prototypical crystalline GST can have various compositions along the pseudobinary tie line and, in its trigonal structure, exhibits a stacked structure along the [111] direction that involve weak van der Waals (vdW) interactions between adjacent blocks. vdW epitaxy represents a powerful way for growing heterostructures made of stacked …