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.