STM study of successive Ge growth on “V”-stripe patterned Si (0 0 1) surfaces at different growth temperatures

The self-assembly process of Ge islands on patterned Si (0 0 1) substrates is investigated using scanning tunneling microscopy. The substrate patterns consist of one-dimensional stripes with “V”-shaped geometry and sidewalls inclined by an angle of 9° to the (0 0 1) surface. Onto these stripes, Ge is deposited in a step-wise manner at different temperatures from 520 °C to 650 °C. At low temperature, the Ge first grows nearly conformally over the patterned surface but at about 3 monolayers a strong surface roughening due to reconstruction of the surface ridges as well as side wall ripple formation occurs. At 600 °C, a similar roughening takes place, but Ge accumulates within the grooves such that at a critical thickness of 4.5 monolayers, 3D islands are formed at the bottom of the grooves. This accumulation process is enhanced at 650 °C growth, so that the island formation starts about 1 monolayers earlier. At 600 and 650 °C, all islands are all aligned at the bottom of the stripes, whereas at 550 °C Ge island form preferentially on top of ridges. The experimental observations are explained by the strong temperature dependence of Ge diffusion over the patterned surface.