Surface Enhanced Quasi-VdW Epitaxy of Magnetic Topological Insulators on III-V substrates at the Boundary of Mass-Transport Flow and Adsorption Control Mode

Magnetic topological insulator could achieve quantum anomalous Hall (QAH) effect and spin-orbit torque (SOT) switching in the same structure. This is promising for its future applications in memory or switching with its robust surface properties by topological protection. GaAs (111) and some other III-V substrates are used a lot for the epitaxy of magnetic insulators. Considering the van der Waals nature of the epitaxial layers, they have very weak van der Waals bonding with the substrate. However, due to the typical stronger interfacial constraints and relatively smaller lattice mismatch, they show a novel quasi Van der Waals epitaxial growth mode. In this mode strain exists and relaxes quickly within the 1st epitaxial layer, while the surface defects quickly get screened within the 1st layer. This has the advantages of both good crystallinity from coherent interfaces, and a less influence from defects and roughness on the substrate surfaces. This is very crucial for achieving the quantization regime.

In this work we have examined hetero-epitaxy of Cr:(Bi_xSb_1-x)₂Te₃ and other magnetic topological insulators on III-V substrates by MBE (Molecular Beam Epitaxy). Simulations are used to compare with both in-situ and ex-situ characterization methods. Growth window of quantization regime are 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.