Micro-Raman imaging of in-plane SiGe alloy nanowires epitaxially grown on Si(001)

Abstract

Silicon-Germanium (SiGe) epitaxial nanostructures are well suited materials for integration into the silicon platform. Among them, nanowires (NWs) are increasingly attracting attention both from a fundamental point of view as well as from the multiple specialized applications that their development may empower in nanoelectronics, thermoelectrics, photovoltaics, energy storage, information and communication technologies. Epitaxially grown SiGe NWs on Si are particularly interesting for device integration and horizontal, in-plane geometries, the optimum choice for manufacturing using planarmicrofabrication technology. In this work, we employ confocal Raman microspectroscopy and imaging to study in-plane gold-seeded SiGe alloy nanowires grown by molecular beam epitaxy (MBE) on Si (001)-oriented wafers which are the usual substrates of standard complementary-metal-oxide-semiconductor (CMOS) technology. The spatial resolution of the Raman images allows us to study individual nanowires. We observe differences in Raman scattering intensity when the light polarization is parallel or perpendicular to the nanowire axis. These variations are correlated to the anisotropic absorption in thin nanowires. Quantitative analysis of the Raman spectra yields the composition and strain variations in the sample, in particular within each nanowire in which we resolve vertical gradients from the base to the top surfaces. These Raman results provide unique insights into the growth processes.