Size-Dependent Silicon Epitaxy at Mesoscale Dimensions.

New discoveries on collective processesin materials fabricationand performance are emerging in the mesoscopic size regime betweenthe nanoscale, where atomistic effects dominate, and the macroscale,where bulk-like behavior rules. For semiconductor electronics andphotonics, dimensional control of the architecture in this regimeis the limiting factor for device performance. Epitaxial crystal growthis the major tool enabling simultaneous control of the dimensionsand properties of such architectures. Although size-dependent effectshave been studied for many small-scale systems, they have not beenreported for the epitaxial growth of Si crystalline surfaces. Here,we show a strong dependence of epitaxial growth rates on size fornano to microscale radial wires and planar stripes. A model for thisunexpected size-dependent vapor phase epitaxy behavior at small dimensionssuggests that these effects are universal and result from an enhancedsurface desorption of the silane (SiH4) growth precursornear facet edges. Introducing phosphorus or boron dopants during thesilicon epitaxy further decreases the growth rates and, for phosphorus,gives rise to a critical layer thickness for single crystalline epitaxialgrowth. This previously unknown mesoscopic size-dependent growth effectat mesoscopic dimensions points to a new mechanism in vapor phasegrowth and promises greater control of advanced device geometries. [ABSTRACT FROM AUTHOR]