X-RAY PHOTOELECTRON-SPECTROSCOPY ANALYSIS OF THE GROWTH-KINETICS OF GE ON SI(001)

The growth kinetics of Ge on Si(001) is determined from the X-ray photoelectron measurements of the Si 2p core level intensity and the Ge 2p3/2 core level intensity as a function of the Ge overlayer thickness. The growth kinetics of the Ge overlayer follow a Stranski-Krastanov growth mode. The critical thickness is almost-equal-to 2.2 ML (where ML means monolayers). The change in the growth kinetics, from a layer-by-layer mode to an island nucleation-and-growth mode is spontaneous. The distribution and the partial relaxation of the misfit strain of this pseudomorphic system are measured by the change in the full width at half-maximum of the Si 2p and Ge 2p3/2 core levels. The strain is found to be confined to the Ge overlayer. Partial relaxation of the misfit strain precedes the transition from the layer-by-layer mode to the island nucleation-and-growth mode. Scanning electron micrographs confirm that the critical thickness occurs in the interval 1.8 ML of Ge to 2.8 ML of Ge. A second transition occurs at almost-equal-to 6.9 ML of Ge and corresponds to the nucleation and growth of large three-dimensional islands.