Chemical vapour deposition of polycrystalline AlN films from AlCl3-NH3 mixtures:: II -: surface morphology and mechanisms of preferential orientation at low-pressure

Polycrystalline AIN films were prepared from AlCl3/NH3 mixtures by chemical vapour deposition (CVD) under low-pressure conditions. Various surface morphologies and preferred orientations were observed, depending on the operating parameters selected. The ammonia flow rate was found to be particularly important in determining the preferred orientation of the deposited layers. The crystal habits were found to be dominated by slow-growing pyramidal and pedion facets. A mechanism based on evolutionary selection was proposed to account for the preferred orientations produced in the layers, but it was also suggested that the orientation of the tiny crystals formed during the early stages of growth is not completely random. Finally, the numerical model developed in our previous article was used to derive a correlation between the fraction of surface covered by ammonia and the final preferred orientation of the deposited layers. (C) 2002 Elsevier Science B.V. All rights reserved.