Low temperature (500-800 degrees C) homoepitaxy of not intentionally doped GaN structures on GaN(0001)/Si (111) seed has been investigated by Vapor-Liquid-Solid (VLS) approach. The growth sequence consists in the metalorganic chemical vapor deposition of a network of submicrometric liquid Ga droplets, followed by their nitridation under flowing ammonia diluted either in H-2 or Ar. When nitridation is performed under Ar carrier gas, GaN growth is very difficult to control due to too high N supersaturation within the droplets, despite very low NH3 flows. Nucleation and growth at the droplets periphery are always favored and, in most cases, high growth rates induce a crust-like growth, forming hollow GaN gangues. The use of H-2 as carrier gas is detrimental to GaN (seed and grown material) stability, for nitridation temperatures >= 700 degrees C. But, compared to Ar atmosphere, a pronounced decrease of N supersaturation is demonstrated, allowing a better control of the growth mode. This is probably a consequence of a lower thermal decomposition efficiency of NH3 at the droplets surface. Optimal growth conditions are found at relatively low temperature (600 degrees C) and NH3 flow (20 sccm) for which a network of well-separated and faceted epitaxial GaN dots or rings is obtained. The growth mechanisms allowing these results are discussed. (C) 2017 Elsevier B.V. All rights reserved.