We have studied the initial stages of island formation and coarsening for epitaxial Ge on vicinal Si (100) using in-situ deposition and nanometer resolution biassed secondary electron imaging (b-SEI) in a UHV-STEM. Ge is deposited using MBE techniques on nominally flat Si(100) substrates as well as those misoriented 1° and 5° toward <110>. The temporal evolution of the islanded microstructure can be studied by analysis of computer generated island size distributions. Good statistics can be obtained for islands with radii between 2nm and lOOnm using high resolution b-SE imaging and a large magnification range. Both MBE and Solid phase MBE (SP-MBE) processes have been studied.
We explain the evolution of the islanded microstructure in terms of competition for Ge adatoms among the various available sinks. For the MBE case, control of diffusion distances by varying the substrate temperature has allowed us to identify effects related to coherently strained and highly dislocated Ge islands as well as contaminant particles. In all cases, coherently strained Ge islands appear to be the weakest sinks and contaminant particles the strongest. Metastable growth of the intermediate layer during interrupted depositions at 375°C may be a direct consequence of an energy cost for incorporating adatoms into coherently strained islands. For depositions at higher temperatures, strong adatom sinks influence nucleation densities and size distributions of Ge islands by reducing the effective supersaturation. Island size distributions analyzed for the case of room temperature deposition in the early stages of coarsening also show evidence of effects due to coherently strained islands. These size distributions evolve from an initial distribution to one with increasing number of large islands while the distribution of the smaller islands (< 10nm radius) remains constant.