SCANNING-TUNNELING-MICROSCOPY STUDY OF GE/GAAS(110) .1. INITIAL NUCLEATION AND GROWTH

Scanning tunneling microscopy (STM) has been used to study the initial nucleation and growth of Ge on GaAs(110) at 420-degrees-C. Multilayer islands of crystalline Ge with heights of four or more layers were formed upon deposition of 0.2 and 0.4 monolayer. We show that the energetics are responsible for the absence of thinner islands and that the energetics account for the Ge island shape. Analysis of the spatial distribution of the islands on the surface demonstrates that there is a depletion zone around each island, the size of which is a measure of the kinetics available during growth. Depletion zones are directly evident in STM images when surface steps are present because they act as preferred nucleation sites. At the same time, island formation at these same steps is not energetically favored, as demonstrated by the movement of Ge islands away from the steps when the surface is annealed at 550-degrees-C.