We have investigated the growth mechanisms of InN on c-plane sapphire substrates with experiments by pulsed laser deposition (PLD) and the first-principles calculation. The first-principles total energy calculations of a sapphire slab with an adatom explain the experimental results such that in-plane alignment between the nitrides and sapphire is [10-10]nitride//[11-20]sapphire. The in-plane alignment mechanism for this case is same as that for GaN and AlN on c-plane sapphire surface. (C) 2004 Elsevier B.V. All rights reserved.