(In,Ga)As Quantum Dot Array Formation by Self-Organized Anisotropic Strain Engineering of an (In,Ga)As/GaAs Quantum Wire
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(In,Ga)As Quantum Dot Array Formation by Self-Organized Anisotropic Strain Engineering of an (In,Ga)As/GaAs Quantum Wire Template: Shallow-Pattern Effects T. Mano, R. Nötzel, G. J. Hamhuis, T. J. Eijkemans, E. Smalbrugge, and J. H. Wolter eiTT/COBRA Inter-University Research Institute, Eindhoven University of Technology P. O. Box 513, 5600MB Eindhoven, the Netherlands ABSTRACT One-dimensional (In,Ga)As quantum dot (QD) arrays are formed on planar singular and shallow-patterned (mesa gratings) GaAs (100) substrates by self-organized anisotropic strain engineering of an (In,Ga)As/GaAs quantum wire (QWR) superlattice (SL) template in molecular beam epitaxy. On planar singular substrates, highly uniform one-dimensional single QD arrays, which are extended over 10 µm length, are realized with efficient photoluminescence. The shallow mesa gratings along [0-11] and [011] induce two different types of steps which differently affect the surface migration processes crucial for QWR template development, i.e., strain driven In adatom migration along [011] and surface reconstruction induced adatom migration along [0-11]. While type-A steps along [0-11] have no significant effect on the adatom migration along [011] and [0-11], type-B steps along [011] hinder the surface reconstruction induced migration along [0-11] to prevent formation of QWR and ordered QD arrays. INTRODUCTION Lateral ordering of self-assembled quantum dots (QDs) is one of the most crucial issues towards device applications. Commonly artificial patterning techniques are used for the position control of QDs [1-4]. These techniques, however, often degrade the structural and optical properties of the QDs. We have recently introduced a new concept for the lateral ordering of QDs based on self-organized anisotropic strain engineering of an (In,Ga)As quantum wire (QWR) superlattice (SL) template [5-9]. Multiple and single one-dimensional InAs or (In,Ga)As QD arrays are realized on planar singular GaAs (100) substrates due to the laterally modulated strain field generated by the underlying QWR templates [6-9]. In this paper, we report on the formation of (In,Ga)As QD arrays by the self-organized anisotropic strain engineering on shallow-patterned GaAs (100) substrates in addition to planar singular ones. On the planar singular substrates, the formation of well-defined QD arrays is optimized. On the shallow-patterned substrates, the influence of surface steps on QD array formation is studied. This establishes the relationship of self-organized anisotropic strain engineering with step engineering on shallow-patterned substrates, providing deeper understanding and opening new routes for further development of this method for QD ordering. EXPERIMENTAL DETAILS The samples were grown by conventional solid-source molecular beam epitaxy (MBE) on both planar singular and shallow-patterned GaAs (100) substrates. The patterned substrates were prepared by optical lithography and wet chemical etching in the H2SO4: H2O2: H2O solution [10]. The periodic mesa gratings with 30
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