GaN layers are selectively grown using ammonia-based metal-organic molecular beam epitaxy (NH(3)-based MOMBE), and the selectivity of the growth is studied by changing the growth temperature. The selectivity of the growth for the mask pattern with a width of 5 pm and a period of 10 mu m obtained for a growth temperature between 650 and 1000 degrees C is superior. This temperature range is much wider than that for conventional MBE. It is attributable to the chemical reaction that occurs in NH(3)-based MOMBE, where the precursors decompose only on the GaN surface. The growth rate between temperatures of 750 and 950 degrees C is found to be higher than that of the entire surface without a mask This result suggests that the adatoms on the mask migrate into the selective growth region, which helps to improve selectivity. The analysis of selective growth with a mask width of 232 mu m revealed that selectivity of the growth is deteriorated. In other words, the effect of migration of Ga adatoms from the mask to the opening is relatively small and the adsorbed atoms tend to form polycrystals on the mask. Consequently, it is found that along with desorption and adsorption of the adatoms, migration of the adatoms is also a very important factor that determines the selectivity of the growth. (C) 2010 Elsevier B.V. All rights reserved.