Control of tensile strain and interdiffusion in Ge/Si(001) epilayers grown by molecular-beam epitaxy
Résumé
Tensile-strained and n-doped Ge has emerged as a potential candidate for the realization of
optoelectronic devices that are compatible with the mainstream silicon technology. Tensilestrained
Ge/Si epilayers can be obtained by using the difference of thermal expansion coefficients
between Ge and Si. We have combined various surface, structural, and compositional
characterizations to investigate the growth mode and the strain state in Ge/Si epilayers grown by
molecular-beam epitaxy. The Ge growth was carried out using a two-step approach: a low temperature
growth to produce relaxed and smooth buffer layers, which is followed by a hightemperature
growth to get high quality Ge layers. The existence of a substrate temperature window
from 260 to 300 C is evidenced, which allows to completely suppress the Ge/Si Stranski-
Krastanov growth. As a consequence of the high temperature growth, a tensile strain lying in the
range of 0.22%–0.24% is obtained. Concerning the effect of thermal annealing, it is shown that
cyclic annealing may allow increasing the tensile strain up to 0.30%. Finally, we propose an
approach to use carbon adsorption to suppress Si/Ge interdiffusion, which represents one of the
main obstacles to overcome in order to realize pure Ge-based optoelectronic devices.