Abstract
In recent years, epitaxial growth of self-assembled quantum dots has offered a way to incorporate new properties into existing solid state devices. Although the droplet heteroepitaxy method is relatively complex, it is quite relaxed with respect to the material combinations that can be used. This offers great flexibility in the systems that can be achieved. In this paper we review the structure and composition of a number of quantum dot systems grown by the droplet heteroepitaxy method, emphasizing the insights that these experiments provide with respect to the growth process. Detailed structural and composition information has been obtained using surface X-ray diffraction analyzed by the COBRA phase retrieval method. A number of interesting phenomena have been observed: penetration of the dots into the substrate (“nano-drilling”) is often encountered; interdiffusion and intermixing already start when the group III droplets are deposited, and structure and composition may be very different from the one initially intended.
Highlights
Semiconductor quantum dots (QDs) have drawn a considerable amount of scientific interest since they provide a means to realize “artificial atoms”—zero-dimensional objects in which the charge carriers are confined in all three dimensions
In this paper we review the results of surface X-ray diffraction (XRD) measurements of several III-V QD systems grown by the droplet heteroepitaxy (DHE) method [24,25]
The samples were grown in a metalorganic vapor phase epitaxy (MOVPE) reactor
Summary
Semiconductor quantum dots (QDs) have drawn a considerable amount of scientific interest since they provide a means to realize “artificial atoms”—zero-dimensional objects in which the charge carriers are confined in all three dimensions This feature gives rise to potential practical applications of quantum mechanical concepts in the fields of opto-electronics [1,2], quantum information [3,4] and energy harvesting [5,6,7]. The ability of X-rays to penetrate into the dots and the substrate makes it possible to investigate both surface and buried structures This property of X-rays in turn makes the scattered signal relatively small, requiring grazing incidence-angle geometry measurements and the use of bright synchrotron radiation sources. To obtain the real space electron density it is necessary to use either complex modeling and fitting or direct methods
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