Highly flat GexSi1−x/Si heterointerfaces grown by molecular beam epitaxy in two-dimensional growth mode

Abstract

Coherent islanding growth of Ge x Si 1− x on a Si substrate has been observed when the epilayer thickness exceeds the transition thickness h t , far below the critical thickness h c , predicted by People and Bean. Once such three- dimensional growth occurs the surface of the epilayer becomes corrugated. In order to obtain highly flat heterointerfaces in a Ge x Si 1− x /Si superlattice grown on a Si Substrate, the Ge x Si 1− x layer thickness must be controlled below h t . Here we present our results of the transition thickness obtained by observing the transition of RHEED pattern during growth. We find that the transition thickness h t is significantly dependent on the growth temperature, as well as on the Ge content x . In a range from 370 to 670°C, h t decreases with increasing growth temperature. So a lower temperature is favorable. This is confirmed by XTEM pictures, X-ray rocking curves and Raman spectra of Ge x Si 1− x /Si superlattices grown at different temperatures. Such a temperature dependence of the transition thickness reveals that kinetics, rather than thermodynamics, is dominant in the growth process.