Metalorganic vapor phase epitaxy of indium nitride (InN) on sapphire was studied and optimized in situ by spectroscopic ellipsometry. Layers with smooth surface morphology were obtained on low-temperature nucleation layers on nitrided sapphire substrates using trimethylindium and ammonia at high V/III ratios above 30 000. Ellipsometry reveals a growth regime for InN below, 550degreesC and best crystalline quality at 500degreesC. Improvement of the crystalline quality is achieved at lower growth temperatures. This tendency is confirmed by X-ray diffraction while still some residual mosaicity of the layers can be observed. The appearance of pronounced El and A, Raman modes, obeying the selection rules of hexagonal InN, confirms the good structural quality of the samples grown. (C) 2002 Elsevier Science B.V. All rights reserved.