We review our attempts to grow a new type of single crystal Si epitaxially
on Si(111). The new single crystal Si is a superlattice of layers that have
twinned and untwinned orientations with respect to the substrate, and is c
alled a twinning superlattice. The Si twinning superlattices are grown usin
g the fact that Si layers grown epitaxially on Si(111) root3 x root3-B have
a twinned orientation with respect to the substrate. We investigate condit
ions for growing twinned epitaxial layers, and clarify that growth of twinn
ed layers requires high surface B concentration and low densities of surfac
e structural defects, such as steps and domain boundaries of the root3 x ro
ot3 reconstruction. We also investigate the thermal stability of the twinne
d layers, and clarify that the temperature at which the twinned layers are
transformed into untwinned layers strongly depends on the thickness. Additi
onally, we establish a technique for measuring crystallographic orientation
s in surface regions in situ during growth. Based on these results, we fina
lly succeed in growing the Si twinning superlattice by repeated growth of S
i with a unit thickness and post-growth annealing. (C) 2001 Elsevier Scienc
e B.V. All rights reserved.