Influence of crystallinity of as-deposited Ge film on formation of quantum dot in carbon-mediated solid-phase epitaxy

The influence of crystallinity of as-deposited Ge films on Ge quantum dot (QD) formation via carbon (C) mediated solid-phase epitaxy (SPE) was investigated. The samples were fabricated.by solid-source molecular beam epitaxy (MBE). Ge/C/Si structure was formed by sequential deposition of C and Ge at deposition temperature (TD) of 150-400 degrees C, and it was heat-treated in the MBE chamber at 650 degrees C. In the case of amorphous or a mixture of amorphous and nano-crystalline Ge film grown for TD 5250 degrees C, density of QDs increased with increasing T-D due to the increase of C-Ge bonds in Ge layer. Ge QDs with diameter of 9.2 2.1 nm were formed in the highest density of 8.3x10(11) cm(-2) for T-D =250 degrees C. On the contrary, in the case of polycrystalline Ge film for T-D 2300 degrees C, density of QDs decreased slightly. This is because C incorporation into Ge layer during SPE was suppressed due to the as-crystallized columnar grains. These results suggest that as deposited Ge film in a mixture of amorphous and nano-crystalline state is suitable to form small and dense Ge QDs via C-mediated SPE.