On epilayer tilt in ZnSe/Ge heterostructures prepared by molecular-beam epitaxy

ZnSe/Ge heterostructures prepared by molecular-beam epitaxy were characterized by ‘‘full-rotation’’ double-crystal rocking curve x-ray analyses with particular emphasis placed on the measurement of tilt between the (400) planes of ZnSe and Ge. It was found that the value of the tilt angle between such planes depends on both the epilayer thickness and the orientation of the substrate plane. A simple model is proposed in the paper of tilt formation and its development. Steps on the substrate surface are shown to be responsible for a redistribution of the bond lengths between the atoms of the substrate and the epilayer in the interface region leading to the formation of tilt between the planes in the epilayer and the substrate. Particular types of stress in the epilayer are shown to affect the final value of the tilt. It was also found that the structural and optical properties of ZnSe/Ge layers appear to be optimized for Ge substrate surface orientations around 2° off (100)→[110].