We haw studied the mechanism of pulsed NH3 growth in metalorganic chemical vapor deposition by investigating the influence of interruption duration of NH3, growth temperature, pressure and NH3 flow rate on the growth behavior of GaN selective area growth (SAG). The essential mechanism of pulsed NH3 is to create a short-term metal-rich growth condition, thus facilitating the growth of {1 0 (1) over bar 1} facets. Optimized pulse duration, growth temperature, pressure and NH3 flow rate balance the amount of Ga atoms on the surface and create an appropriate metal-rich condition, resulting in an enhanced lateral growth rate by dramatically increasing the growth rate of {1 0 (1) over bar 1} facet. We have achieved hexagonal GaN plates with flat c-plane top surfaces and {1 0 (1) over bar 0} vertical sidewalls on substrates with a fill factor of about 0.1%. The understanding of pulsed NH3 growth technique will significantly promote the preparation of crystals by SAG or epitaxial lateral overgrowth, especially on substrates with a very low fill factor. (C) 2015 Elsevier B.V. All rights reserved.