Self-Oriented Polycrystalline InP Nanowires Guided by Nanogrooves and Their Near-Infrared Photoresponse

This study demonstrates the self-oriented growth of polycrystalline indium phosphide (InP) nanowires aligned along nanogrooves on annealed M-sapphire substrates via a catalyst-free chemical vapor deposition process. Morphological characterizations reveal that the nanowires have a highly oriented arrangement, along with a rough surface texture. Structural analyses confirm their polycrystalline nature, which is characterized by distinct grain boundaries and variable crystallite orientations. Angle-resolved polarized Raman spectroscopy uncovers an intermediate anisotropic ratio (1.85) between bulk InP (1.27) and single-crystalline nanowires (2.32), reflecting the interplay of one-dimensional geometry and polycrystallinity. Two-terminal devices fabricated by directly depositing electrodes on the nanowires exhibit significant photoresponses in the near-infrared range, although the photocurrent diminishes over several seconds. This extended response time is attributed to the polycrystalline nature of these nanowires, which results in a decreased electron mobility. The long-lasting photocurrent dynamics align with synaptic plasticity time scales, highlighting the potential of these nanowires for neuromorphic optoelectronics, particularly in artificial synaptic devices. This work advances the synthesis of oriented polycrystalline nanostructures and provides insights into tailoring optoelectronic properties through crystallinity engineering.