Influence of lateral growth on the optical properties of GaN nanowires grown by hydride vapor phase epitaxy

GaN nanowires (NWs) are synthesized on Si (111) using vapor–liquid–solid hydride vapor phase epitaxy at low temperature (740–780 °C). We find that the flow rate of the GaCl (HCl) gas has a large impact on the NW lateral growth rate, which affects the NW morphology, axial growth rate, and optical property. Upon increasing the flow rate of GaCl, the uncatalyzed vapor solid lateral growth increases rapidly, leading to variations in NW morphology from wire-like to tower-like and rod-like. The photoluminescence spectrum shows a broad red luminescence (RL) at around 660 nm and a weak near-band-edge luminescence at around 400 nm when lateral growth is at a significant level. Furthermore, spatially resolved cathodoluminescence and high-resolution transmission electron microscopy observations confirmed that this RL originates from the defective lateral growth. Finally, by inhibiting the lateral growth, GaN NWs with a high aspect ratio and excellent crystal quality (no RL observed at around 660 nm) were successfully synthesized with a rapid growth rate of 170 μm/h.