interface*

Intrinsic Magnetic Topological Insulator (MTI) has been widely recognized as an excellent platform to study topological surface states critical for understanding exotic quantum phenomena. Using molecular beam epitaxy (MBE), we gain control of high-quality MnBi₂Te₄ thin films on Si (111) and epitaxial graphene substrates, as well as Bi₂Te₃/ MnBi₂Te₄ heterostructure. By combining several in-situ characterization techniques, we gain critical insights into the contribution of anti-site defects on the electronic structure of MBE-grown MnBi₂Te₄ films and Bi₂Te₃/ MnBi₂Te₄ heterostructures. Specifically, we map out the chemical potential and Dirac point of the thin films grown. Then, we further report the observation of Mn out-diffusion behavior across the abrupt interface on Bi₂Te₃/ MnBi₂Te₄ heterostructure. These scientific insights secure the foundation for understanding effective doping via anti-site defects and pave the way for the future applications of MBE for magnetic topological insulators and their heterostructures for emerging topological quantum materials.