Role of As in the Anisotropic Positioning of Self-Assembled InAs Quantum Dots
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Role of As in the Anisotropic Positioning of Self-Assembled InAs Quantum Dots Fabrizio Arciprete1, Ernesto Placidi1,2, Rita Magri3, Massimo Fanfoni1, Adalberto Balzarotti1, and Fulvia Patella1 1 Dipartimento di Fisica, Università di Roma “Tor Vergata”, Via della Ricerca Scientifica 1, I00133 Roma, Italy, 2 CNR-ISM, Via Fosso del Cavaliere 100, I-00133 Roma, 3 Dipartimento di Fisica, Università di Modena e Reggio Emilia, and Centro S3 CNR-Istituto Nanoscienze, Via Campi 213/A, 4100 Modena, Italy. ABSTRACT Progress in tailoring the size, shape and positioning of Quantum Dots on the substrate is crucial for their potential applications in new optoelectronic devices for nano-photonics as well as in quantum information and computation. Using Molecular Beam Epitaxy in pulsed deposition mode we demonstrate that the nucleation of InAs Quantum Dots can be selectively guided on the GaAs(001) surface by a suitable choice of the kinetic parameters for the growth of both the GaAs buffer layer and the InAs Quantum Dots. By developing a two-species rate-equation kinetic model we show that the positioning of the Quantum Dots on only one side of mounds of the GaAs buffer can be traced back to the very small As flux gradient between the two mound slopes ) caused by the proper tilting of the incoming As flux. Such gradient ( originates, at the relatively high growth-temperature, a net cation flow from one slope of the mound to the other that is responsible for the selective growth. INTRODUCTION During the last decade, the growth of highly strained semiconductor heterostructures has been studied extensively, especially those systems which exhibit a Stranski-Krastanov (SK) growth mode. The SK growth mode, in fact, represents an appealing approach for obtaining defect-free self-assembled Quantum Dots (QDs) [1, 2]. Recently, the attractive prospects of QDs have been demonstrated in the case of sophisticated applications in new generation devices such as single-photon emitters for nano-photonics and quantum computing for which a control of the islands' lateral position is essential. Such control can be obtained, for example, by standard lithography [3-5] or by multilayer stacking [6-8]. The former, although selective and flexible, introduces defects that may severely decrease the optical properties of QDs while the latter is limited by the poor control of the islands' position. Alternatively, a significant and appealing challenge would be to control the islands' position by a careful tailoring of the growth process. Here we demonstrate that the position of InAs islands grown on GaAs can be effectively controlled by means of a suitable choice of the kinetic parameters for the growth of both the GaAs buffer layer and the InAs islands. We show that, at relatively high growth temperatures, QDs nucleation along oriented step bunching (mounds) can be selectively obtained as a function of the As4 flux direction, so resulting in an almost completely anisotropic surface distribution of QDs on the mound structures of the GaAs buffer. These results h
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