Optimization of Si–C reaction temperature and Ge thickness in C-mediated Ge dot formation

Abstract

To form Ge dots on a Si substrate, the effect of thermal reaction temperature of sub-monolayer C with Si (100) was investigated and the deposited Ge thickness was optimized. The samples were prepared by solid-source molecular beam epitaxy with an electron-beam gun for C sublimation and a Knudsen cell for Ge evaporation. C of 0.25 ML was deposited on Si (100) at a substrate temperature of 200°C, followed by a high-temperature treatment at the reaction temperature (TR) of 650–1000°C to create Si–C bonds. Ge equivalent to 2 to 5nm thick was subsequently deposited at 550°C. Small and dense dots were obtained for TR=750°C but the dot density decreased and the dot diameter varied widely in the case of lower and higher TR. A dot density of about 2×1010cm−2 was achieved for Ge deposition equivalent to 3 to 5nm thick and a standard deviation of dot diameter was the lowest of 10nm for 5nm thick Ge. These results mean that C-mediated Ge dot formation was strongly influenced not only by the c(4×4) reconstruction condition through the Si–C reaction but also the relationship between the Ge deposition thickness and the exposed Si (100)-(2×1) surface area.