InN layers were grown on both-sides-polished (0 0 0 1) freestanding GaN substrates by hydride vapor-phase epitaxy (HVPE) in the growth temperature range from 450 to 650 degrees C with an input partial pressure of NH3 ranging from 3.0 x 10(-2) to 3.8 x 10(-1) atm. An In-polar InN layer was grown on the (0 0 0 1) Ga-polar surface, while a N-polar InN layer was grown on the (0 0 0 (1) over bar) N-polar surface of the freestanding GaN substrate. The InN layers of both polarities grown at 550 degrees C had smooth surfaces, ideal lattice constants of the wurtzite InN structure, and a minimum optical absorption edge energy of about 0.75 eV. Surface morphologies of the InN layers were also dependent on the NH3 input partial pressure. The surface of In-polar InN became smoother under a high NH3 input partial pressure, whereas the N-polar InN required a low NH3 input partial pressure to achieve a smooth surface. (C) 2009 Elsevier B.V. All rights reserved.