Axially graded heteroepitaxy and Raman spectroscopic characterizations of Si1−xGex nanowires

Abstract

We report the axially graded heteroepitaxy of Si1−xGex nanowires, by the kinetic controls of the Au-catalytic decomposition of precursors during chemical vapor syntheses. Transmission electron microscope studies demonstrate that the relative composition of Si and Ge is continuously graded along the uniformly thick nanowires, sharing the same crystal structures with the continuously varying lattices. We also employed a confocal Raman scattering imaging technique, and showed that the local variations in Raman phonon bands, specific to Si and Ge alloying (νSi–Si, νSi–Ge, and νGe–Ge), can be spatially and spectrally resolved along the individual nanowires, within the spatial resolution of ∼500nm.

Anomalous junctions characterized by Raman spectroscopy in SixGe1−x nanowires with axially degraded components

“…The Raman peak shift of phonon band ( Si-Si in nanowire) agrees well with Ref. 15, although only two different points were measured in Si 1Àx Ge x nanowires in Ref. 15.…”

“…15, although only two different points were measured in Si 1Àx Ge x nanowires in Ref. 15. Two other Raman peaks almost did not shift in Ref.…”

“…15. In the CVD growth process, 15 the inlet gas composition (or ratio) between SiH 4 and GeH 4 should be changed continually to grow the Si 1Àx Ge x nanowires with axially degraded components.…”

“…To generate devices with special functions, nanowire junctions, 1,2 axial heterojunction, 3-8 core-shell junction, [9][10][11][12][13][14] and axially graded heteroepitaxy 15 are grown by different ways. The methods include ultrahigh vacuum evaporation technique, 16 molecular beam epitaxy, 17 laser-assisted catalytic growth, 18,19 and chemical vapor deposition (CVD).…”

On‐Nanowire Band‐Graded Si:Ge Photodetectors

“…[ 18 ] GeH 4 fl ow rate is maintained at the relatively lower level than that of SiH 4 in our syntheses to effectively suppress an unwanted tapered NW growth during the Ge-rich segment growth, and guarantees a uniform NW diameter throughout the entire growth sequence. [ 16 , 17 , 26 ] The high resolution transmission electron microscope (TEM) images in Figure 1 c and d taken from the marked spots in Figure 1 b demonstrate that the Si:Ge NW of 40 nm in diameter coherently maintains the [011] directions along the NW axis.…”