Heteroepitaxial Growth of GaAs on Ge(111) and Ge(100) by MOCVD

GaAs heteroepitaxy on Ge(100) is an established route for III-V-on-IV integration, yet growth on non-(100) orientations, such as (111), remains underexplored. Here, we systematically investigate the growth of GaAs/Ge(100)–6° and GaAs/Ge(111) by metalorganic chemical vapor deposition (MOCVD) using triethylgallium (TEGa) and arsine (AsH 3 ) precursors at various substrate temperatures and precursor flows. Atomically smooth GaAs surfaces on Ge(111) with root mean squared (RMS) roughness as low as 0.35 nm were realized at 650 °C. Varying the AsH 3 flow reveals a coupling between smoothness and twin density, with a 240 sccm AsH 3 flow yielding virtually twin-free films with <1 nm RMS roughness. In contrast, the (100)–6° orientation showed a stronger morphological sensitivity with AsH 3 flow, exhibiting roughening below 120 sccm. X-ray diffraction─both high-resolution (HR-XRD) and three-dimensional (3D-XRD)─and electron microscopy─scanning (SEM) and high-angle annular dark field scanning transmission (HAADF-STEM)─reveal low twin density films below 0.01% on the optimized Ge(111) and defect-free layers with minimal roughening at the GaAs/Ge interface. Atomic resolution energy-dispersive X-ray spectroscopy (EDS) reveals that the GaAs polarity is (111)B. These results define the first MOCVD growth parameter map for GaAs/Ge(111), demonstrating scalable, low-defect, polarity-controlled epitaxy suitable for integrating GaAs-based devices on group-IV platforms.