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HL: Fachverband Halbleiterphysik

HL 30: Poster I

HL 30.21: Poster

Dienstag, 17. März 2020, 13:30–15:45, P3

Atomic structure of GaAs_xP_1−x surfaces during MOCVD-preparation — •Agnieszka Paszuk, Oliver Supplie, Jan Philipp Stöckmann, Harita Gordhanbhai Rupapara, Peter Kleinschmidt, and Thomas Hannappel — Institute of Physics, University of Technology Ilmenau, Germany

Low defect GaAs_xP_1−x graded buffers grown on Si enable highly efficient III-V-on-Si multi-junction solar cells. The As/P content of individual GaAsP graded buffer layers can be quantified in situ during metalorganic chemical vapor phase deposition with reflection anisotropy spectroscopy (RAS) due to a characteristic spectral fingerprint of the GaAsP surfaces [1]: With increasing As supply, a peak close to the GaP E₁ critical point energy shifts towards GaAs E₁ at lower energy. Here, these RAS fingerprints are correlated with the surface reconstructions and chemical composition identified in UHV by LEED and XPS, respectively. We show that the surface structure of GaAsP buffers depends on the GaAsP stoichiometry and post-growth process route. GaAsP surfaces with low As content exhibit P-rich, (2x1) reconstructed surfaces. LEED patterns of GaAsP buffers with 50% of As in the bulk exhibit a mix of (2x1) reconstruction with additional spots present at third order. We find both P-P and As-As dimers present at this surface. The same buffers annealed additionally at 500^∘C exhibit As-rich (2x4) reconstructed surfaces, whereas annealing at 700^∘C leads to Ga-rich surfaces. Future studies are aimed to resolve the actual atomic structure of the complex surface unit cell. [1] O. Supplie et al., Proceedings 45th IEEE PVSC Conf. (2018) 3923.