Pre-structuring of silicon substrates to investigate MBE-growth of SiGe layers

We have used e-beam lithography and reactive ion etching (RIE) to pattern (100) Si substrates prior to overgrowth with SiGe alloys by molecular beam epitaxy (MBE). The structuring process was designed to give lines with well defined width and orientation as well as a defect free Si crystal surface. Using atomic force microscopy, it was shown that the relaxation of SiGe buffer layers strongly depends on the width and the orientation of the mesa lines. A significant reduction in the dislocation density compared to the unpatterned areas of the samples can be obtained. The photoluminescence spectra of the SiGe buffers and Si quantum wells (QWs) grown on top of buffer layers confirm the non-isotropic relaxation process in the line shaped mesas. This method reveals novel possibilities for the manufacture of Si-based electronic devices.