High temperature refractive indices of GaN

Undoped GaN (u-GaN) films were grown by low pressure metalorganic vapour phase epitaxy (LP-MOVPE) on sapphire substrates. In situ optical monitoring was applied to the growth process either using a LayTec EpiR-DA TT spectroscopic reflectometer or Filmetrics F30. Refractive indices of u-GaN films at 1060 degrees C were obtained in a spectral range from 370-900 nm. A peak at 412 5 rim in refractive index spectra was observed, which most likely corresponds to the band-gap of hexagonal GaN at a temperature of 1060 degrees C. Refractive indices below this band-gap are fitted well to the first-order Sellmeier formula. As an example of the applications of the refractive indices, the effective film thicknesses of GaN during the resumption from 3 dimensional (3D) to 2 dimensional (2D) growth have been calculated from the spectra recorded by a LayTec system using the optical constants obtained. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.