Supporting Information: The mechanism of Ni-assisted GaN nanowire growth Carina B. Maliakkal, Nirupam Hatui, Rudheer D. Bapat, Bhagyashree A. Chalke, A. Azizur Rahman, and Arnab Bhattacharya Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Mumbai 400005, India A. Estimating actual growth temperature Temperature ( o C) 790 760 770 780 3000 3500 4000 4500 Time (s) Time (s) 2000 3000 4000 5000 800 500 600 700 400 Si Si on sapphire Si Si on sapphire FIG. S1: Temperature measured by emissivity corrected in-situ pyrometry on Si pieces directly in the susceptor pocket and on top of a sapphire wafer. The temperature difference across a 330 μm sapphire wafer is thus found to be ∼ 30 ◦ C. The graphite susceptor used in the showerhead MOCVD reactor has three pockets of 2” diameter. But the sapphire substrates used for NW growth are just ∼ 1 cm × 1 cm in size. In order to avoid the deposition of GaN in the susceptor pockets and to avoid nickel contamination of the system, 2” diameter, 330 μm thick, “dummy” c-sapphire wafers were placed in all the pockets. The Ni(NO 3 ) 2 .6H 2 O-coated growth samples were placed on top of these c-sapphire wafers. So, the growth temperature is going to be much lesser than the thermocouple setpoint. 1