Unraveling the Nature of Coherently Strained Interfaces in Quasi van der Waals Epitaxy of Cr:(BixSb1-x)2Te3 on GaAs (111) Substrates for Quantum Anomalous Hall Effect

Quasi van der Waals Epitaxy (qvdWE) has been realized for decades at the interfaces between 3D and 2D materials or van der Waals materials, and has recently been utilized for the epitaxial growth of various van der Waals materials. The growth of magnetic topological insulators (MTI) Cr: (BixSb1-x)2Te3 (CBST) on GaAs (111) substrates for Quantum Anomalous Hall Effect (QAH) is actually one of the examples of qvdWE, which is not well noticed despite the fact that its advantages have been used in growth of various MTI materials. This is distinguished from the growth of MTIs on other substrates. Although the qvdWE mode has been used in many 2D growth on some III-V substrates, the specific features and mechanisms are not well demonstrated and summarized yet. Here in this work, we have for the first time shown the features of both coherent interfaces and the existence of strain originating from qvdWE at the same time. Hetero-epitaxy of Cr:(BixSb1-x)2Te3 and other magnetic topological insulators on III-V substrates by MBE (Molecular Beam Epitaxy). Simulations are used to compare both in-situ and ex-situ characterization methods. Growth window of quantization regime is also studied. By controlling source flux and substrate temperatures, we have identified the growth of samples with quantum anomalous Hall effect at the boundary of mass-transport flow and adsorption-control mode on GaAs (111) substrates. With our work, now it becomes clear that the magnetic topological insulators Cr: (BixSb1-x)2Te3 (CBST) grown on GaAs (111) substrate for quantum anomalous Hall effect (QAHE) has the coherently strained interfaces.