Investigations on the role of Ni-catalyst for the VLS growth of quasi-aligned GaN nanowires by chemical vapor deposition

We report the fabrication of quasi-aligned GaN nanowires (NWs) on Si(111) substrate by chemical vapor deposition using Ni as a catalyst. The structural and composition analysis of Ni-catalyst on the apex of the GaN NWs were investigated using high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. The catalyst contains only Ni–Ga alloy with the composition of ~66:33 having Ni₃Ga phase. GaN NWs exhibit wurtzite structure without any amorphous sheath layer or cubic inclusions, where the catalyst contains the mixture of both the crystalline and amorphous phases. During growth, the nitrogen radicals are expected to migrate on the surface of the catalytic droplet to incorporate into the growing lattice via the solid–liquid interface due to poor solubility of N in Ni, which forbids the alloying of nitrogen with Ni. Temperature-dependent photoluminescence reveals that the intensity of donor-bound exciton (D⁰X) peak consistently increases with a blue shift as the temperature decreases. The D⁰X peak is centered at 3.467 eV for 10 K. Interestingly, yellow band, the characteristic nature of defects-induced luminescence, is absent in Ni-catalytic-assisted growth of GaN NWs.