Integration of nanocrystal quantum dots with crystalline semiconductor substrates: Structure, Stability, and Optical res
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Integration of nanocrystal quantum dots with crystalline semiconductor substrates: Structure, Stability, and Optical response Atul Konkar, Siyuan Lu, Anupam Madhukar Nanostructure Materials & Devices Laboratory University of Southern California, Los Angeles, CA 90089-0241 Steven. M. Hughes and A. Paul Alivisatos Department of Chemistry University of California, Berkeley, CA 94720 ABSTRACT Integration of epitaxical and colloidal semiconductor nanostructures into hybrid structures can potentially open unprecedented functionalities and applications. We present here some results of a study of the structural and optical nature of adsorbed InAs nanocrystal quantum dots (NCQDs) on GaAs(001) substrates containing buried nanostructures, providing the first evidence of excitation transfer from NCQDs to the substrate. Results are also presented for the overgrowth of GaAs on the InAs NCQDs, addressing the all important issue of approach to removal of the chemical contamination left behind by the solvent during adsorption of the NCQDS. It is shown that high structural and optical quality buried integrated structures are feasible, thus opening a new field of investigation. INTRODUCTION Vapor phase epitaxically grown semiconductor quantum structures, such as quantum wells and quantum dots, have emerged as the basis of a large part of the active devices in modern optoelectronic information sensing and communication systems [1]. The last decade has seen an emphasis on III-V quantum dots, particularly on the so-called self-assembled quantum dots (SAQDs) based upon the spontaneous 3-dimensional (3D) coherent island formation in strained epitaxy [2]. In parallel, colloidal chemistry based semiconductor nanocrystals have also emerged as another class of quantum nanostructures, particularly suitable for applications in solution environments such as biological labeling [3], as well as in noncrystalline (e.g. polymer) matrix environments [4]. Each of these classes of quantum structures offers some unique and complementary functionalities. However, if monolithically integrated as schematically indicated in figure 1, together these two classes of quantum structures can open unprecedented quantum dot architectures, functionalities, and applications. Motivated by such considerations, we embarked upon such an examination utilizing, as a vehicle, the integration of the InAs/GaAs based epitaxical quantum wells and dots that are at the heart of the near infrared regime optoelectronics technology and InAs/ZnSe based colloidal nanocrystal quantum dots (NCQDs). In this paper we report some of our findings on the structure of the as-deposited InAs NCQDs on GaAs(001), their optical response, and the structural and optical behavior of these nanocrystals upon molecular beam epitaxical overgrowth of GaAs capping layers. A fundamental challenge in overgrowth is discovering procedures that allow recovery from the chemical contamination resulting from the process of deposition of the NCQDs from their solution environment. Usual procedures of thermal
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