Dependence of Al layer growth mode on Cr underlayer thickness in molecular-beam epitaxy of (001) Al/Cr superlattices

摘要

It has been found that (001) Al layers grow on Cr layers in the Stranski-Krastanov (SK) mode T. Kingetsu, Y. Kamada, and M. Yamamoto, J. Appl. Phys. 87, 159 (2000). In the present study, the dependence of the growth behavior of (001) Al/Cr superlattices on the thickness of Cr layers in molecular-beam epitaxy was investigated, using in situ reflection high-energy electron diffraction and ex situ x-ray diffraction analyses. The (001) epitaxial growth proceeds with an orientational relationship of Al(001)010‖Cr(001)110, in the cases where the Cr layer thickness is three monolayers or larger. The critical thickness of the SK growth, the maximum thickness of the two-dimensional growth at the early stage, depends on the thickness of the Cr underlayers. The critical thickness is two monolayers when the Cr underlayer thickness is four monolayers or greater, while the critical thickness increases to three monolayers when the Cr underlayer thickness is reduced to three monolayers. Postdeposition evolution of Al three-dimensional islands also depends on the Cr underlayer thickness, although the thickness where the three-dimensional islands start to occur is about three monolayers in both cases. In the cases where the Cr layer thickness is two monolayers or smaller, epitaxial growth of the superlattices is found to be unstable.