Polarized Raman scattering and localized embedded strain in self-organized Si/Ge nanostructures

Using polarized Raman spectroscopy, we examine different vibrational modes (i.e., Si-Si, Si-Ge, and Ge-Ge) in Si/Ge self-organized nanostructures. Here, we present unambiguous proof that multilayers of Ge nanometer-size, "dome-shaped" islands grown on a <100> Si substrate are nearly fully relaxed and that the built-in strain field is substantially localized in the surrounding Si matrix. In contrast, multilayers with "pyramid-shaped" islands do not show observable relaxation. The large strain in the Si layers of the multilayer dome samples correlates with the greater self-organization in these structures compared to the multilayer pyramid samples. (C) 2003 American Institute of Physics.