RHEED and SIMS studies of germanium segregation during growth of SiGe/Si heterostructures; a two-site exchange model with growth rate dependence

Segregation of Ge during the formation of SiGe/Si heterojunctions in thin f ilm epitaxial growth is perhaps the largest obstacle to the formation of th e desirable atomically sharp interfaces in device structures. This process has been studied experimentally using reflection high-energy electron diffr action (RHEED), secondary ion mass spectrometry (SIMS) and numerically usin g a two-site exchange model. In this paper, the current two-site exchange m odel is modified to incorporate the growth process explicitly in the rate e quation. This allows the extraction of analytical solutions in the dilute r egime and provides a better insight into the influence of temperature and o ther parameters on the eventual composition profiles across the Si/SiGe het erojunction. Using numerical methods, the rate equation is solved for pract ical conditions and compared with experimental measurements by RHEED and SI MS. The dependence of composition profiles on the growth rate is demonstrat ed by the model and good agreements with experimental data without modifyin g the Gibbs energy of segregation (C) 2000 Elsevier Science B.V. All rights reserved.