Journal
JOURNAL OF CRYSTAL GROWTH
Volume 591, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.jcrysgro.2022.126714
Keywords
A3. Molecular beam epitaxy; A. Spectroscopic ellipsometry; B. Topological insulator; B.Bi2Se3; A. Dielectric function; A. Thickness control
Funding
- NSF [DMR-2004812, DMR-2039351]
- Two-Dimensional Crystal Consortium - Materials Innova-tion Platform [DMR-2039351]
- Graduate School, Southern Illinois University Carbondale
- 2DCC-MIP, Pennsylvania State University
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In-situ spectroscopic ellipsometry (SE) analysis provides more precise dielectric functions and thicknesses of multilayer heterostructures, allowing for detection of subtle changes during growth processes.
Multilayer heterostructures of the topological insulator Bi2Se3 and conventional semiconductor In2Se3, as well as solid solution layers of (Bi1-xInx)(2)Se-3 layers were grown by molecular beam epitaxy and analyzed in-operando using spectroscopic ellipsometry (SE). SE spectra were obtained after the deposition of each layer to deter-mine the respective dielectric functions and thicknesses of each layer. In contrast to ex-situ SE, where uncertainty in the dielectric function and thicknesses of individual layer impose limitations to extract a correct model for the dielectric function of such multilayer heterostructures from a single set of SE data, the step-by-step in-situ SE data recover more precise dielectric functions for Bi2Se3, In2Se3, (Bi0.7In (0.3))(2)Se-3 and the cap-layer. The optical models developed for multilayer structures can decipher minute perturbations in layers as the growth progresses. Our models show that a ~ 7 nm Bi2Se3 layer grown next to a sapphire substrate seems to disappear as the structure is annealed at 600 C. Finally, when the dielectric functions were represented as a collection of Kramers-Kronig-consistent oscillators, in-situ SE predicted the quality of films; the weighted-average broadening parameter for oscillators used for Bi2Se3 films grown on (Bi0.7In (0.3))(2)Se-3 layer is-20% smaller compared to Bi2Se3 films directly grown on sapphire, confirming that the former film is of better quality, and providing a direct metric to quantify film quality and defect concentration. These conclusions were corroborated by transport data.
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