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Micro-Raman spectroscopy and imaging of epitaxial SiGe nanowires grown on Si(001)

AuthorsAlonso Carmona, M. Isabel ; Bailo, E.; Garriga Bacardi, Miquel ; Molero, A.; Vaccaro, Pablo Óscar ; Goñi, Alejandro R. ; Ruiz, A.; Alonso, María
Issue Date2015
CitationRehearsal meeting & Workshop with the Scientific Advisory Board (2015)
AbstractSilicon-Germanium (SiGe) epitaxial nanostructures are suitable materials for integration into the silicon platform. Nanowires (NWs) are one of their most interesting morphologies both from fundamental as well as practical point of view. Their development can lead to specialized functionalities for different fields of application such as nanoelectronics, thermoelectrics, photovoltaics, energy storage, information and communication technologies. Epitaxially grown SiGe NWs on Si (001)-oriented wafers are particularly interesting for device integration to preserve the compatibility with standard microfabrication technology. We have studied the formation of SiGe epitaxial in-plane NWs by Molecular Beam Epitaxy (MBE) on Si (001) substrates by using AuSi seeds obtained by annealing Au layers deposited on clean Si surfaces. We find conditions in which an homogeneous growth of in-plane NWs not mixed with other nanostructure geometries is achieved. The NWs grow along the [110] directions and their lateral dimensions depend on the seed nanoparticle sizes, as is typical for a vapor-liquid-solid (VLS) process. In this contribution, we show confocal Raman microspectroscopy and imaging results of these samples, where individual NWs can be studied within the spatial resolution of the system. Quantitative evaluation of the spectroscopic information reveals intriguing composition and residual strain distributions that help us to understand the growth processes. In particular, the results indicate that the Si1-xGe x composition seems to be mainly determined by the liquid-solid thermodynamic equilibrium given by the AuSiGe phase diagram. In the used conditions of flux and substrate temperature, it is possible to grow different compositions x from the Ge-rich end to a Si-rich value of x ~ 0.3. The NWs evolution is dominated by the surface diffusion kinetics of the Ge adatoms. The strain distributions, with both tensile and compressive residual values, are also consequence of the Ge kinetic behavior. In addition, the Raman intensity of the substrate provides a probe to investigate the optical absorption of the NWs. 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.
DescriptionPoster presented at the Rehearsal meeting & Workshop with the Scientific Advisory Board, held in Barcelona (Spain) on October 2-3th, 2015.
Appears in Collections:(ICMM) Comunicaciones congresos
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