Ge dots formation using Si(100)-c(4×4) surface reconstruction

•Effect of carbon coverage, Ge thickness and growth temperature on Ge dots formation was investigated.•Small and dense dots were formed at the carbon coverage of 0.25 ML.•Dot density of about 1.8×1010 cm−2 was achieved for Ge thickness and temperature of 4 nm and 400 ˚C, respectively.•Standard deviation of dot diameter was the lowest of 12 nm at Ge=4 nm.

An effect of Si(100)-c(4×4) surface reconstruction by using sub-monolayer carbon reaction was investigated to form Ge dots on a Si (100) substrate. Samples were prepared by a solid-source molecular beam epitaxy system with an electron beam gun for carbon (C) sublimation and a Knudsen cell for Ge evaporation. C of 0.1 to 0.5 ML was deposited on Si (100) at the substrate temperature of 200 ˚C, followed by a high-temperature treatment at 1000 ˚C to react C with Si. Ge equivalent to 3 nm thick was subsequently deposited at 450 ˚C. The densest dots were obtained for C coverage of 0.25 ML because the Si surface was stabilized by C for c(4×4) reconstruction without leaving excessive C. To investigate effects of Ge deposition thickness and temperature on Ge dot morphology, Ge equivalent to 3 to 5 nm thick was deposited at 400 and 450 ˚C in the case of 0.25-ML C. The most uniform and densest Ge dots were formed at the Ge deposition thickness and temperature of 4 nm and 400 ˚C, respectively. These results indicate that the Ge deposition should be optimized along the condition of the surface reconstruction via the C–Si reaction.