Regensburg 2019 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe

HL: Fachverband Halbleiterphysik

HL 41: Heterostructures, interfaces, and surfaces

HL 41.7: Vortrag

Donnerstag, 4. April 2019, 16:45–17:00, H31

Optical in situ spectroscopy during MOCVD-preparation of GaAs_1−xP_x surfaces — •Ammar Tummalieh, Agnieszka Paszuk, Oliver Supplie, Alexander Heinisch, Peter Kleinschmidt, and Thomas Hannappel — Institute for Physics, University of Technology, Ilmenau, Germany

Multi-junction solar cells comprising GaAsP top absorbers with Si bottom cells enable photovoltaic conversion efficiencies above 40%. However, monolithic epitaxial integration of GaAsP with As contents between 50%-75% on Si requires to overcome a significant lattice mismatch. Commonly, this is achieved with GaAsP graded buffers where the As/P ratio increases step-wise. Here, such GaAs_1−xP_x buffers (x≤0.5) were grown on GaP(100) substrates by metalorganic chemical vapor deposition. The entire process was monitored in situ with reflection anisotropy spectroscopy (RAS), an optical surface sensitive technique, in order to yield a better understanding of the interface preparation. To further resolve the origin of the RA spectra and the atomic structure of the surfaces, selected samples were transferred to ultra-high vacuum surface-sensitive tools. The atomic structure depends on processing routes: While GaAsP surfaces annealed under H₂ at 500^∘C exhibit (2x4) surface reconstruction and are V-rich, annealing at 700^∘C leads to Ga-rich surfaces. We also find that the GaAs_1−xP_x stoichiometry can be quantified empirically during growth via the stoichiometry-depending energy shift of the E₁ interband transition of GaAsP.