Formation and dissolution of InAs quantum dots on GaAs

In situ reflection high energy electron diffraction (RHEED) has been used t o study the time evolution during self-assembled molecular beam epitaxy (MB E) growth of InAs quantum dots on GaAs. Using a special data acquisition te chnique, two characteristic time constants are determined very precisely: t he time t(c) up to the first appearance of InAs dots and the time t(f) it t akes to complete the 2D-3D transition of all islands. Surprisingly, we find that t(c) increases with temperature which disagrees with a thermally acti vated process. In contrast to this, t(f) behaves Arrhenius-like and an acti vation energy of E-f similar or equal to 0.39 eV is determined. Furthermore , the sum t(c) + t(f) does not depend significantly on temperature and corr esponds to an InAs coverage of similar or equal to 2.0 monolayers. A second focus of this paper is the study of dissolution of InAs dots after interru ption of the As flux. From the experiments, an activation energy of 3.2 eV for desorption of In located on top of the wetting layer is determined, whe reas direct desorption from the wetting layer corresponds to an activation energy of 3.4 eV. (C) 2000 Elsevier Science B.V. All rights reserved.