Large-Scale Self-Catalyzed Growth of Dense GaAs Nanowires with Near-Unity Vertical Yield and Lot-to-Lot Reproducibility on SiO _<i>x</i> /Si(111) Wafers via Droplet Etching

Building on the established Ga droplet etching (DE) technique on SiOx, we report a scalable and reproducible method for the self-catalyzed vapor–liquid–solid growth of GaAs nanowires (NWs) on 2-in. SiOx/Si(111) wafers using molecular beam epitaxy. By systematically varying only the Ga deposition time during DE, the number density of vertical NWs can be tuned over 2 orders of magnitude (from low-107 to high-108 cm–2). We identify a threshold Ga deposition time above which uniform, untapered NW arrays with high-density (>108 cm–2) and near-unity vertical yield (>99%) are obtained, exhibiting low reflectance (<1%) across the visible to near-infrared range, thereby demonstrating a wafer-scale antireflective “black” material. The sample possesses the thinnest GaAs parasitic layer, suggesting sufficient surface modification of the native oxide on the Si substrate enables efficient utilization of incident Ga and As4 atoms for vertical NW growth. By fine-tuning the Ga deposition time without altering any other growth parameters, this work investigates the role of Ga deposition time in DE and establishes a single in situ calibration protocol that enables reproducible NW growth across different substrate lots.