GE ISLANDS ON SI(111) AT COVERAGES NEAR THE TRANSITION FROM 2-DIMENSIONAL TO 3-DIMENSIONAL GROWTH

We use scanning reflection electron microscopy (SREM) to study three-d imensional Ge island formation on the Si(lll) surface at coverages nea r the transition from two-dimensional to three-dimensional growth unde r Ge Buses between 0.001 and 0.02 BL/s and at temperatures between 380 and 690 degrees C. The SREM images clearly show that the formation of flat three-dimensional islands with large lateral dimensions is domin ant at higher temperatures. An average critical island size of about n ine atoms was obtained from the Bus dependence of island density. The existence of such large size critical islands is supported by the inte rmediate formation of the second Ge bilayer before island nucleation, which then decomposes, and by the rapid saturation of island density. From the temperature dependence of island density the activation energ y for a Ge atom to detach from the islands to form an adatom was estim ated to be similar to 1.1 eV. (C) 1998 Elsevier Science B.V. All right s reserved.