BIMODAL HEIGHT DISTRIBUTION OF SELF-ASSEMBLED GERMANIUM ISLANDS GROWNON SI0.84GE0.16 PSEUDO-SUBSTRATES

We have investigated the size distribution of germanium islands deposi ted onto a Si0.84Ge0.16 buffer layer, by atomic force microscopy. The size distribution was found to be bimodal at 630-740 degrees C and con sisted of one group of smaller 'pyramidal' islands with a broad distri bution of diameters and heights and another group of larger 'spherical ' islands with a narrow distribution of diameters and heights. Both th e size of the islands and the critical size for the change-over betwee n the two growth modes are strongly temperature-dependent and decrease with decreasing temperature. To explain the origin of this bimodality , we have conducted experiments where the amount of material and the t emperature were varied. We suggest that the bimodal size distribution and the temperature-dependent change-over between the two growth modes can be explained by an interplay between energetics and kinetics. (C) 1998 Elsevier Science S.A. All rights reserved.