Diffusion in Si_xGe_1−x/Si Nanowire Heterostructures

Abstract

Si0.48Ge0.52/Si tip/nanowire heterostructures were grown by pulsed laser vaporization (PLV) at a growth temperature of 1100 degrees C. Ge diffusion in [111]-growth Si nanowires was studied for different post-synthesis annealing temperatures from 200 degrees C to 800 degrees C. Ge composition profiles were quantified by energy-dispersive X-ray spectroscopy in a transmission electron microscope. The compositional profiles were modeled by a limited-source diffusion model to extract temperature-dependent diffusion coefficients. The Ge diffusion coefficients followed an Arrhenius relationship with an activation energy of 0.622 +/- 0.050 eV. This rather low activation energy barrier is similar to the previously reported activation energy barrier of 0.67 eV for Ge surface diffusion on Si, suggesting that surface diffusion may dominate in nanowires at this length scale.

Equilibrium strain-energy analysis of coherently strained core–shell nanowires

“…While we model the /10 0S growth axis in this paper, it should be noted that the Si x Ge 1Àx nanowire growth directions are predominantly /111S, /110S, and /11 2S when grown via vapor-liquid-solid techniques [22][23][24][25][26], although /10 0S Si nanowire arrays can be fabricated by bottom-down lithography and etching approaches [27]. Since Si and Ge are elastically anisotropic, having a Zener ratio of 1.56 and 1.67, respectively, the stress and strain states will be dependent on the growth axis; however, the qualitative conclusions of the elasticity calculations will be similar.…”

Diameter Dependence of Ge-doped Si Nanowires Fabricated via Vapor-Liquid-Solid Growth

“…SiH 4 and GeH 4 are used as precursor gases in an H 2 carrier gas on oxidized Si wafers coated with thin (~2 nm) Au films. SiH 4 and GeH 4 are used as precursor gases in an H 2 carrier gas on oxidized Si wafers coated with thin (~2 nm) Au films.…”