Influences of hydrogen input partial pressure in the carrier gas (F degrees = P degrees(H2)/(P degrees(H2) + P degrees(N2))) on the crystalline quality and polarities of InN on GaAs (1 1 1)A surfaces were investigated by metalorganic vapor phase epitaxy (MOVPE). It was found that the polarity of the InN was affected by the hydrogen gas in the system regardless of the polarity of GaAs starting substrate. The polarity of InN layer grown with the hydrogen partial pressure of F degrees = 0.004 was a mixture of In-polarity and N-polarity, while that grown with F degrees = 0 was In-polarity. Degradation of the crystalline quality of InN grown with F degrees = 0.004 occurred due to the polarity inversion during the growth. The reason why the polarity of InN was influenced by the hydrogen carrier gas could be explained by the preferential growth of N-polarity InN in the H-2 contained ambient and/or the limiting reaction of InN decomposition. (C) 2007 Elsevier B.V. All rights reserved.