Formation and dissolution of InAs quantum dots on GaAs

In situ re#ection high energy electron di!raction (RHEED) has been used to study the time evolution during self-assembled molecular beam epitaxy (MBE) growth of InAs quantum dots on GaAs. Using a special data acquisition technique, two characteristic time constants are determined very precisely: the time t # up to the "rst appearance of InAs dots and the time t & it takes to complete the 2D}3D transition of all islands. Surprisingly, we "nd that t # increases with temperature which disagrees with a thermally activated process. In contrast to this, t & behaves Arrhenius-like and an activation energy of E & K0.39 eV is determined. Furthermore, the sum t # #t & does not depend signi"cantly on temperature and corresponds to an InAs coverage of K2.0 monolayers. A second focus of this paper is the study of dissolution of InAs dots after interruption of the As #ux. From the experiments, an activation energy of 3.2 eV for desorption of In located on top of the wetting layer is determined, whereas direct desorption from the wetting layer corresponds to an activation energy of 3.4 eV. ( 2000 Elsevier Science B.V. All rights reserved.

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