GeSi films with reduced dislocation density grown by molecular-beam epitaxy on compliant substrates based on porous silicon

To grow high-quality heteroepitaxial layers, we propose a compliant silicon substrate consisting of a thin epitaxial silicon film on a high-density po rous layer as a membrane and an expansive low-density porous layer as a mec hanical damper which shields the overlying layers from the massive wafer. G eSi films over the critical thickness have been grown by molecular-beam epi taxy on these substrates. Transmission electron microscopy analysis shows t hat Ge0.2Si0.8 films have no dislocations owing to just elastic strain rela xation whereas plastic flow in the pseudomorphic films that are being grown on conventional Si substrates occurs with generation of dislocations in a regular manner. The experimental data on porous silicon structure are prese nted in some detail and are briefly discussed in connection with substrate compliance. (C) 1999 American Institute of Physics. [S0003-6951(99)05052-4] .