We have grown numerous samples under Hg-deficient conditions, in order to study the formation of void defects. The surface morphology of all samples grown was characterized using optical and SEM microscopy. At the same time, the substrates were, studied prior to nucleation using in situ spectroscopic ellipsometry (SE). We find a correlation between the ellipsometric signal prior to nucleation and the final morphology of the layers grown. We studied the Hg layer present at the surface before nucleation by RHEED, XPS and SE. A better model is proposed, which reflects the physical characteristics of the substrate surface. (C) 2603 Elsevier B.V. All rights reserved.