Structural analysis of imperfect GeSi superlattices grown on Ge(001) substrates

Abstract

By combining the complementary techniques of x-ray diffraction and transmission electron microscopy we have been able to accurately determine the structure of imperfect GeSi superlattices (SL’s). The samples were epitaxially grown on Ge(001) substrates using Si2H6 and GeH4 source gases. In this report, details of the x-ray experiment and analysis are emphasized. In particular, a model is presented for calculating the diffracted intensity from a SL containing gradients in composition and thickness. Applying this model to the data it is found that between the first and last layers of each SL there exists a roughly 10% increase in the growth rate, without a corresponding change in the alloy composition. This is attributed to a slow increase in the substrate temperature, Tsub, of just a few degrees. A sample grown with a corresponding gradual decrease in the control temperature, TC, was found to be much more uniform.