Optical In Situ Studies of Ge(100) Interfacial Exchange Reactions in GaAs-Rich MOVPE Reactors for Low-Defect III-P Growth

For vertical-cavity surface-emitting lasers (VCSELs) or photoelectrochemical devices and high efficient III-V/Ge(100) photovoltaics, preparation of double-atomic steps on Ge(100) substrates is highly recommended in order to avoid anti-phase boundaries in the III-V buffer layers. These Ge(100) surfaces were investigated in detail under As- and GaAs-rich MOVPE reactor conditions. During initial growth of III-P buffer layers, however, on an atomically well-ordered Ge(100):As surface, As-P exchange takes place, during which double-layer steps should be preserved. Here, we apply in situ monitoring to study the interaction of P with vicinal Ge(100):As surfaces under realistic, GaAs-rich CVD reactor conditions at growth temperature. In situ optical spectroscopy in combination with surface science techniques in ultra-high vacuum ambience is used to investigate the Ge(100) surface. We show that different Ge(100):As/P heterointerfaces are formed depending on the applied molar flow of phosphorus precursors. Despite the lattice-matched quality of the probing III-P layer, this critical heterointerface impacts significantly the surface roughness and the formation of crystal defects in the subsequently grown III-P buffer layers.