Tunable Ge content and thickness in hemispherical-shell shaped SiGe recess channels created by proximal Ge nanospheres

We report the novel tunability of Ge content, thickness, and even curvature/shape in self-aligned, hemispherical-shell shaped SiGe recess channels created in Si substrates by Ge nanospheres that are proximally located to these nanoshells. The hemispherical recess SiGe nanoshells arise from the migration of Ge interstitials through the intervening oxide layer between the Ge nanospheres and the Si substrate, and their Ge content, thickness, and curvatures exhibit a monotonic dependence on the depth of penetration of the Ge nanospheres into the Si substrate. Following a unique "explosion" phenomenon in which the Ge nanosphere breaks up into multiple nanocrystallites, both the Ge content and thickness of the SiGe nanoshells are significantly decreased by reverse migration of Ge interstitials from the SiGe nanoshells to the Ge nanocrystallites.