AFM and RHEED study of Ge islanding on Si(111) and Si(100)

Strain relaxation and clustering of Ge thin films grown on Si(111) and Si(100) by molecular beam epitaxy (MBE) have been studied in situ with reflection high energy electron diffraction (RHEED) and analyzed by atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS). At low temperature, growth is dominated by island nucleation and by strain relief through island formation. The cluster size distribution (measured by AFM) just after the 2D–3D growth mode transition is broader than that for ‘late-stage’ growth (when diffusion gradients dominate cluster growth) and is well fit by a model in which the surface diffusion of adatoms is described by a random walk. At high temperature, growth is dominated by dislocation formation and the aspect ratio of the islands changes. The barrier to dislocation formation is reduced at step bunches; thus, islands nucleate preferentially at the step bunches and grow along them. By understanding Ge island nucleation and evolution, we hope to grow a population of uniformly-sized nanocrystals exhibiting quantum confinement effects.