Chapter 9 Spectroscopic Characterization of Gallium Nitride Nanowires Umesh Rizal and Bibhu Prasad Swain Introduction Nanometer-scale structures represent an emerging and rapidly expanding area of research due to photon, phonon, and electron confinement. The large surface to volume ratio, constrain at the molecular level and change in the phonon density of states have great impact on the process related properties of material. In this regard, GaN-NWs with wide direct band gaps of 3.4 eV, considered as novel material for fabrication of blue/green light emitting diodes, developing nanoscale emitters, detec- tors, biological/chemical sensors, laser diodes, and high-temperature devices [1]. The selection of catalyst is important parameter in the growth process of GaN-NWs. The catalyst influences the nucleation at the initial stage. The following important factors decides the formation of GaN-NWs (a) eutectic temperature of metal and GaN alloys, (b) surface energy of catalysts during dissociation, (c) adatom vapor pressure inside the reactor, (d) adatom vapor pressure inside catalyst particles. Lee et al. have synthe- sized GaN nanorings, nanoribbons and smooth nanowires on MgO substrate using Ag catalyst and observed that the diameter of GaN-NWs varies from 10–20 nm and length extended up to 500 μm[2]. Maliakkal et al. successfully synthesized Ni catalyzed GaN-NWs of diameter 20–130 nm and length extended up to 6 μm using MOCVD [3]. Kuykendall et al. synthesized vertical GaN-NWs of diameter 15–200 nm using Fe catalyst [4]. Chen et al. deposited GaN-NWs via conventional APCVD process using In catalyst and found that the diameter of NWs varies from 10 U. Rizal (B ) Department of Chemistry, Sikkim Government College, Upper Kamrang, Namchi South Sikkim, Sikkim 737126, India e-mail: umeshrizal680@gmail.com B. P. Swain (B ) Department of Physics, National Institute of Technology Manipur, Langol, Imphal, Manipur 795004, India e-mail: bpswain@nitmanipur.ac.in; bibhuprasad.swain@gmail.com © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 B. P. Swain (ed.), Nanostructured Materials and their Applications, Materials Horizons: From Nature to Nanomaterials, https://doi.org/10.1007/978-981-15-8307-0_9 173