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The study of the exotic properties of the surface states of topological insulators requires defect-free and smooth surfaces. This work aims to study the enhancement of the surface morphology of optimally doped, high-crystalline (Bi0.4Sb0.6)2Te3 films deposited by molecular beam epitaxy on Al2O3 (001) substrates. Atomic force microscopy shows that by employing an in situ thermal post anneal, the surface roughness is reduced significantly, and transmission electron microscopy reveals that structural defects are diminished substantially. Thence, these films provide a great platform for the research on the thickness-dependent properties of topological insulators.

The success of GeSn alloys as active material for infrared lasers could pave the way toward a monolithic technology that can be manufactured within mainstream silicon photonics. Nonetheless, for operation on chip, lasing should occur at room temperature or beyond. Unfortunately, despite the intense research in recent years, many hurdles have yet to be overcome. An approach exploiting strain engineering to induce large tensile strain in micro‐disk made of GeSn alloy with Sn content of 14 at% is presented here. This method enables robust multimode laser emission at room temperature. Furthermore, tensile strain enables proper valence band engineering; as a result, over a large range of operating temperatures, lower lasing thresholds are observed compared to high Sn content GeSn lasers operating at similar wavelength.