Beneficial defects: exploiting the intrinsic polishing-induced wafer roughness for the catalyst-free growth of Ge in-pla
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NANO EXPRESS
Open Access
Beneficial defects: exploiting the intrinsic polishing-induced wafer roughness for the catalyst-free growth of Ge in-plane nanowires Luca Persichetti1*, Anna Sgarlata2, Stefano Mori2,3, Marco Notarianni4, Valeria Cherubini2, Massimo Fanfoni2, Nunzio Motta4 and Adalberto Balzarotti2
Abstract We outline a metal-free fabrication route of in-plane Ge nanowires on Ge(001) substrates. By positively exploiting the polishing-induced defects of standard-quality commercial Ge(001) wafers, micrometer-length wires are grown by physical vapor deposition in ultra-high-vacuum environment. The shape of the wires can be tailored by the epitaxial strain induced by subsequent Si deposition, determining a progressive transformation of the wires in SiGe faceted quantum dots. This shape transition is described by finite element simulations of continuous elasticity and gives hints on the equilibrium shape of nanocrystals in the presence of tensile epitaxial strain. PACS: 81.07.Gf; 68.35.bg; 68.35.bj; 62.23.Eg Keywords: Nanowires; Epitaxy; Silicon; Germanium; Quantum dots
Background In the last few years, germanium (Ge)-based nanoelectronics is living a second youth. This renewed interest stems from recent advances in high-κ dielectrics technology compatible with Ge and has been prompted by the advantageous electrical properties of Ge compared to Silicon (Si) [1,2]. On the roadmap of continuous scaling of transistors with higher operation speed, Ge is ranked among the most promising alternate materials for integration into the Si platform, due to the high mobility and saturation velocity leading to effective device performance combined with reduced power consumption [3]. Ultrascaled Ge-based electronics nonetheless is still in its infancy, and extensive fundamental research on Ge nanofabrication is required so that these appealing semiconductor properties could compensate for the high material costs. Novel quantum-related properties due to scaled dimensionality have stimulated the quest for fabricating one-dimensional nanostructures like nanowires (NWs) which have demonstrated great potential for applications * Correspondence: [email protected] 1 Department of Materials, ETH Zurich, Hönggerbergring 64, Zürich 8093, Switzerland Full list of author information is available at the end of the article
in a variety of fields such as high-temperature thermoelectrics [4], super-efficient lithium ion batteries [5], and new-generation photovoltaics [6]. In this context, Ge NWs are particularly promising, owing to the smaller bandgap and the larger exciton Bohr radius of Ge, which provide quantum confinement effects at larger nanowire sizes compared to Si [7]. One major hurdle for technological application of NWs is to develop a growth method combining synthesis and assembly in a single step, hopefully also being compatible with traditional planar device architecture. Ge NWs are usually grown by vapor-liquid-solid (VLS) mechanism [8-10]. In this process, the metal seed, which is required as catalyst, is left
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