“…The deposition of GaN is conduced typically at temperatures of 1000 °C, usually adopting ammonia and trimethylgallium (TMGa) as reactants with a V−III ratio (NH 3 /TMGa) higher than 1000, and hydrogen as the carrier gas. , Major problems encountered during the growth of high-quality films are represented both by the absence of a homoepitaxial substrate, so that films are usually deposited on sapphire, which has a lattice mismatch of 14% with GaN, and by the presence of severe parasitic gas-phase reactions. These undesired reactions lead to the formation of GaN gas-phase adducts and thus determine the nucleation of particles formed by several gallium, nitrogen, carbon, and hydrogen atoms. − Once generated, GaN powders can adsorb on the reactor walls or the growth surface, thus affecting the film quality, though this process is contrasted by thermal diffusion, which hinders the diffusion of heavy particles toward hot surfaces if a sufficient thermal gradient is present. The formation of gas-phase particles is an important technological problem because it is associated with the following: loss of precursors, which will not be available for deposition; fouling of the reactor, which must therefore be cleaned periodically; formation of stable intermediate species of relatively low molecular weight, thus only slightly affected by thermal diffusion, which might adsorb on the surface in positions that might not be epitaxial and thus give rise to the formation of defects, such as stacking faults …”