Atomic surface control of Ge(100) in MOCVD reactors coated with (Ga)As residuals

Abstract Heteroepitaxy of planar, low-defect III-V semiconductor layers on Ge(100) requires a single-domain substrate surface, where dimer rows are aligned in parallel on atomically well-ordered terraces, which are separated by steps of even numbered atomic height. The presence of Ga and As in the sample ambience crucially impacts the preparation of such Ge(100) surfaces. Ga and As are commonly omnipresent, when applying metalorganic chemical vapor deposition (MOCVD), either directly supplied by precursors, in the form of MOCVD reactor residuals, or both. We study the impact of the growth conditions on the Ge(100) surface formation in situ, in dependence on the reactor pre-conditioning, the type of As supply, and/or temperature, utilizing surface-sensitive reflection anisotropy spectroscopy. We benchmark the in situ spectra to in system X-ray photoelectron spectroscopy, low energy electron diffraction and scanning tunneling microscopy. We find that interaction of tertiarybutylarsine (TBAs) with a coating of the inner MOCVD reactor walls by GaAs residuals favors desorption of As from reactor parts resulting in As-dimers on the Ge(100) surface, which are rotated by 90° compared to preparation routes employing TBAs in Ga-free ambience. The optical in situ control enables precise adjustment and switching between distinct Ge(100) surface reconstructions for subsequent III-V heteroepitaxy.