Nitridation of Sapphire as a Precursor to GaN Growth: Structure and Chemistry

Abstract

Nitridation of sapphire substrates is used as precursor to the growth of GaN films to provide a wetting layer which is closer in terms of structure and chemistry to the overlayer. Nitridation has been carried out by metalorganic chemical vapour deposition at 530ο, 800o and 1100oC in an environment of NH3 and H2. The structure and chemistry of the nitrided layer grown at these different temperatures has been studied by x-ray photoelectron spectroscopy, electron diffraction, high resolution electron microscopy and electron energy loss spectroscopy. The low temperature nitridation process results in a nitrided layer in which oxygen has been partially replaced by nitrogen to form a cubic spinel- AlxOyNz structure. Nitridation at 800o and 1100oC results in complete substitution of oxygen atoms by nitrogen to form a cubic rock salt AlN structure. These structures are stable on thermal anneal at 1000oC prior to epitaxial GaN growth.