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The realization of n-type conduction in directly bottom-up grown Si-doped GaAs nanowires (NWs) by molecular beam epitaxy has remained a long-standing challenge. Unlike the commonly employed vapor–liquid−solid growth, where the amphoteric nature of Si dopants induces p-type conduction, we report a completely catalyst-free, selective area molecular beam epitaxial growth that establishes n-type behavior under Si doping. The vapor–solid selective area growth on prepatterned Si (111) substrates is enabled by an important in situ substrate pretreatment to create an As-terminated 1 × 1-Si(111) substrate necessary for the growth of [111]-oriented GaAs:Si NWs with a large aspect ratio and high yield. Correlated resonant Raman scattering and single-NW micro-photoluminescence (μPL) experiments confirm the n-type nature of the Si-doped GaAs NWs evidenced by a dominant SiGa local vibrational Raman mode, a distinct band filling effect (up to > 10 meV) along with increased PL peak broadening upon increased Si concentration. Excessive Si doping is further found to induce some auto-compensation evidenced by red-shifted PL and the appearance of minor SiAs and SiGa–SiAs pair-like local vibrational Raman modes. Employing excitation power dependent μPL, we further discern signatures in below-gap defect luminescence (∼1.3–1.45 eV) arising from structural defects and Si dopant-point defect complexes.The realization of n-type conduction in directly bottom-up grown Si-doped GaAs nanowires (NWs) by molecular beam epitaxy has remained a long-standing challenge. Unlike the commonly employed vapor–liquid−solid growth, where the amphoteric nature of Si dopants induces p-type conduction, we report a completely catalyst-free, selective area molecular beam epitaxial growth that establishes n-type behavior under Si doping. The vapor–solid selective area growth on prepatterned Si (111) substrates is enabled by an important in situ substrate pretreatment to create an As-terminated 1 × 1-Si(111) substrate necessary for the growth of [111]-oriented GaAs:Si NWs with a large aspect ratio and high yield. Correlated resonant Raman scattering and single-NW micro-photoluminescence (μPL) experiments confirm the n-type nature of the Si-doped GaAs NWs evidenced by a dominant SiGa local vibrational Raman mode, a distinct band filling effect (up to > 10 meV) along with increased PL peak broadening upon increased Si concentrat...