Deposition of high-density Ge quantum dots on ultra-thin SiO2/Si(1 1 1) film surface

High-density Ge quantum dots (QDs) have been grown on Si(1 1 1) surface covered by a ultra-thin SiO2 film whose thickness, determined by synchrotron radiation photoelectron spectroscopy (SRPES), is about one monolayer (ML). The influences of substrate temperature and Ge thickness have been demonstrated by in situ reflection high-energy electron diffraction (RHEED) and ex situ atomic force spectroscopy (AFM). The experimental results show that at 500 °C, Ge adatoms can create nucleus by reacting with the oxide film and then produce uniform and dense Ge QDs. The QDs in form of “frustum of tetrahedron” can be formed at 650 °C, which case is similar with the growth on Si(1 1 1) surface. According to the growth results under different Ge thicknesses, 0.5-nm-thick (1.60 ML) Ge is necessary for the production of QDs, which indicates quantitatively that Ge QDs’ growth on ultra-thin SiO2 surface does not follow the Stranski–Krastanov (S–K) mode. After depositing 1.1-nm-thick Ge, Ostwald ripening process occurs.