Formation of Ge quantum dots on Si substrate using consecutive deposition of Ge/C and in situ post annealing

Effects of intermediate carbon between amorphous Ge and Si surface on formation of Ge dots recrystallized through post-annealing were studied. The samples were prepared by solid-source molecular beam epitaxy system with electron beam gun for C sublimation and K-cell for Ge evaporation. C and Ge were deposited sequentially at 200 °C and Ge/C/Si was subsequently annealed in MBE chamber. Ge dots were formed at annealing temperature (T_A) of 400 °C for Ge(1 nm)/C(0.25 ML)/Si. The dot size increased with T_A, and both Ge(2 2 0) peak intensity measured by in-plane XRD and dot density were the highest at T_A of 700 °C. A strong correlation between dot density and surface roughness indicated recrystallization of Ge occurred during the dot formation promoted by Si-C bonds. Concerning the effect of C coverage, there was an optimum at 0.25 ML which gave good crystallinity of Ge dots. Coalesced dots with bad crystallinity were observed for less or more C coverage. This was considered that dot formation combined with S-K growth mode due to large bare Si surface occurred at small C coverage and excess C incorporated into Ge dots at large C coverage. In terms of Ge thickness, there was also an optimum at 1 nm to provide sufficient Ge atoms without excess.