Molecular Beam Epitaxial Growth and Nonlinear Optical Signatures of Single-Domain Bi2Se3

We report a new approach to enhance the photonic response of thin-film topological insulator Bi2Se3 by significantly reducing twin domains and antiphase disorder. The strategy employs closely lattice-matched trigonal substrates combined with surface structuring to preferentially seed a single rotational domain before epitaxy. Characterization using optical second harmonic generation (SHG), nonlinear optical tensor analysis, X-ray diffraction, and atomic force microscopy confirms the near-single crystal Bi2Se3 heteroepitaxial layers. These results show a clear six-fold symmetric sin2(3ϕ) SHG pattern at normal incidence, and a vanishingly small 100-to-1 peak-height ratio from X-ray pole-scans showing negligible twinning. These results show that this approach can yield near perfect single crystal heteroepitaxial Bi2Se3 whose photonic properties converge to those of bulk-grown single crystals.