Figure 4: Material properties and photochemical activity of p-GaN/p-In_0.20Ga_0.8N nanowires.

(a) Schematic of the double-band GaN/In_0.20Ga_0.8N nanowire heterostructure illustrating different layers incorporated during growth for efficient photon absorption and water-splitting reaction. Five segments of InGaN were incorporated along the growth axis of GaN nanowires. The concept of double-band photocatalyst is illustrated in the inset. (b) Room temperature μ-PL spectrum from as-grown p-GaN/p-In_0.20Ga_0.8N nanowire heterostructure. (c) STEM-HAADF image of a single p-GaN/p-In_0.20Ga_0.8N nanowire reveals the existence of In_0.20Ga_0.8N segments in GaN nanowire. The inset shows EDXS elemental mapping on the selected region of the p-GaN/p-In_0.20Ga_0.8N nanowire, showing the distribution of In, Ga and N. Scale bar, 50 nm. (d) H₂ and O₂ evolution rates in overall water splitting with AM1.5G filter, and with different long-pass filters. Visible light activity is clearly demonstrated. The inset shows a schematic of core/shell Rh/Cr₂O₃ nanoparticle decorated double-band p-GaN/p-In_0.20Ga_0.8N nanowire photocatalyst on Si substrate. The error bar is defined by the s.d. (e) A snapshot of H₂ and O₂ gas bubble formation from neutral water under full arc illumination with AM1.5G optical filter on a p-GaN/p-In_0.20Ga_0.8N sample (Supplementary Movie 1). A ∼3 cm² sample (active GaN/In_0.2Ga_0.8N catalyst weight ∼0.48 mg) was glued on a microscopic glass and immersed in neutral pH water for overall water splitting. Scale bar, 2 cm. (f) SEM image of the p-GaN/p-In_0.20Ga_0.8N nanowire after ∼6 h of water splitting, demonstrating the stability of nanowires and Rh/Cr₂O₃ co-catalyst. Scale bar, 1 μm.