Self-assembled germanium nanocrystals on SiC{0001}

The self-organized growth of Ge islands on various hexagonal SiC{0001} surfaces is discussed. The formation of two (2-D) or three-dimensional (3-D) Ge islands depend on the polarity of the SiC substrate (silicon or carbon face), the SiC surface stoichiometry and reconstruction, the growth rate and temperature. Furthermore, the nucleation conditions can be modified by an oxidation of the Si-adlayer present on Si-rich SiC surfaces. On the Si face of SiC(0001)-(√3×√3)R30°, 2-D Ge islands of lateral dimensions between 2 and 4 nm and a density of more than 1012 cm−2 are initially formed on a 0.3 nm thick Ge wetting layer. Similar to Si substrates, a further growth leads to the formation of equilibrium 3-D Ge nanocrystals of typically more than 20 nm in size and a density of about 1010 cm−2. A Ge deposition on the C face of SiC, as well as on the oxidized Si adlayer of a Si face of SiC results in small 3-D Ge islands of only a few nanometers in size and a number density between 1011 and 1012 cm−2.