Germanium an SiC(0001):: Surface structure and nanocrystals

Germanium nanocrystals as potential candidates for a future optoelectronics in group-IV semiconductors have been grown on SiC(0001). A monoatomic wetting layer is formed hi a Stranski-Krastanov growth mode. The surface structure of this wetting layer studied by STM and LEED depends on the SIC surface preparation. 3x3 and 4x4 Ge superstructures are observed by growing on the silicon-rich SiC(0001)-3x3 surface. Surface structures with mainly two-fold periodicity as well as 6x6 are observed after Ge deposition on silicon-deficient SiC(0001)-(root 3x root3)-R30 degrees or (6 root 3x6 root3) surfaces, Two-dimensional Ge islands of lateral dimensions between 2 and 4 nm and a density of 3 * 10(12) cm(-2) are initially formed on the wetting layer to reduce strain. Further deposition results in the growth of nanocrystals of lateral dimensions between 40nm and 150nm and heights between 5 and 30nm. A maximum density of 10(10) cm(-2) and minimum size of these nanocrystals has been obtained for low deposition temperature of 470 degreesC and high rate of 1.5nm/min. The epitaxial orientation of the nanocrystals has been determined as (111) and (220) by TEM and XRD.