Strong preferential (100) orientation is observed for the first time in the CdTe thin films directly grown on Si(100) substrates without any buffer layers. This result is attributed to the fact that the epilayer is grown directly on the hydrogen-terminated Si substrate without any preheating treatment. The crystal qualities of CdTe(100)/Si(100) and CdTe(111)/Si(111) epilayers obtained at the same growth conditions were compared. Atomic force microscopy observations reveal different surface morphology at the early stages of the crystal growth for CdTe(111)/Si(111) and CdTe(100)/Si(100) epilayers, implying that they are governed by different growth mechanisms. The nucleation of CdTe(100)/Si(100) starts with 3D islands having a dome shape. It is demonstrated that the height and diameter distributions narrow and the aspect ratio decreases with decreasing the growth time. The crystallinity of CdTe(100)/Si(100) epilayers is inferior to that of CdTe(111)/Si(111) due to a double-domain structure. (c) 2004 Elsevier B.V. All rights reserved.