Ge segregation mechanism during Si/Ge multilayer growth

The Ge segregation mechanism during Si/Ge multilayer growth has been invest igated using medium-energy ion scattering (MEIS) and computer simulation wi th the stochastic Monte Carlo technique. We found that Ge atoms segregated not only in the topmost layer but also in the second and third layers. The segregation probability is found to be quadratic in the Ge concentration at the surface. The exchange between the second and the third layer also occu rs readily during growth, even although these layers are buried and therefo re are not expected to reduce the surface free energy. We found that the ac tivation energy for the site exchange process at the subsurface is lower th an the previously believed value, and flip-flop exchange at the subsurface plays a more important role in the Ge segregation process. (C) 1999 Elsevie r Science S.A. All rights reserved.