Chemical Nano-tomography of Self-assembled Ge-Si:Si(001) Islands from Quantitative High Resolution Transmission Electron
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1184-HH01-09
Chemical Nano-tomography of Self-assembled Ge-Si:Si(001) Islands from Quantitative High Resolution Transmission Electron Microscopy Luciano A. Montoro1, Marina S. Leite1, Daniel Biggemann1, Fellipe G. Peternella1, K. Joost Batenburg3, Gilberto Medeiros-Ribeiro1,2 and Antonio J. Ramirez1 1
Brazilian Synchrotron Light Laboratory, P.O. Box 6192, Campinas SP 13084-971, Brazil Hewlett-Packard Laboratories, P.O. Box 10350, Palo Alto, California 94303-0867, USA 3 University of Antwerp, Universiteitsplein 1, B-2610, Wilrijk, Belgium 2
ABSTRACT The knowledge of composition and strain with high spatial resolution is highly important for the understanding of the chemical and electronic properties of alloyed nanostructures. Several applications require a precise knowledge of both composition and strain, which can only be extracted by self-consistent methodologies. Here, we demonstrate the use of a quantitative high resolution transmission electron microscopy (QHRTEM) technique to obtain two-dimensional (2D) projected chemical maps of epitaxially grown Ge-Si:Si(001) islands, with high spatial resolution, at different crystallographic orientations. By a combination of these data with an iterative simulation, it was possible infer the three-dimensional (3D) chemical arrangement on the strained Ge-Si:Si(001) islands, showing a four-fold chemical distribution which follows the nanocrystal shape/symmetry. This methodology can be applied for a large variety of strained crystalline systems, such as nanowires, epitaxial islands, quantum dots and wells, and partially relaxed heterostructures.
INTRODUCTION The growth of 3D semiconductor islands in heteroepitaxial systems and the study of their physical properties have been a very active area of research, principally because of their optical and electronic properties. An accurate control of the shape, size, composition and elastic strain of the islands is a crucial step for the application of these nanostructures in the quantum devices. Fluctuations on the composition inside of these nanostructures are a key factor that determine their structural properties and, as a consequence, the associated physical properties [1]. The GeSi islands grown on Si(001) have emerged as prototypical model system for the study of selfassembled semiconductors nanocrystals. This assumption stems from the fact that only two elements are involved, which are completely miscible in one another, and for exploring the conventional Si technology. The properties of Si-Ge:Si(001) have been studied extensively using a number of techniques, including atomic force microscopy combined with selective chemical etching [2], X-ray absorption fine structure [3], transmission electron microscopy (TEM) [4,5] and grazing incidence anomalous X-ray diffraction [6,7]. All support the existence of vertical and radial composition variations, with most of the Si at the base of the island and the Ge concentration increasing monotonically from the base to the top. Scanning Transmission Electron Microscopy (STEM) has also b
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