Strain-relaxed SiGe/Si heteroepitaxial structures of low threading-dislocation density

A new method of stepwise equilibration for molecular beam epitaxy (MBE) gro wth of relaxed, low dislocation-density Si1-xGex alloy layers on a (001)-Si substrate is presented. The stepwise buffer is prepared in a layer-by-laye r manner. The growth of each layer includes two main stages, a low temperat ure stage and an average-temperature stage, which allows to separate the pr ocesses of nucleation and multiplication of misfit dislocations and thr pro pagation of the threading dislocations. An in situ equilibration annealing at considerably high temperature is implemented before the next growth step to remove the threading dislocations from the layer. The dislocation morph ology in these stepwise graded Si1-xGex buffers is investigated by transmis sion electron and atomic force microscopy. The ability to grow fully strain relaxed, almost dislocation-free, virtual substrates of different composit ions is demonstrated. (C) 2000 Published by Elsevier Science S.A. All right s reserved.