Interface Engineering in Type-II CdSe/BeTe Quantum Dots
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Interface Engineering in Type-II CdSe/BeTe Quantum Dots Sergey V. Ivanov1, Tatiana V. Shubina1, Sergey V. Sorokin1, Alexey A. Toropov1, Reginald N. Kyutt1, Alla A. Sitnikova1, Magnus Willander2, Andreas Waag3 and Gotfried Landwehr4 1 Ioffe Physico-Technical Institute of RAS, St.Petersburg 194021, RUSSIA 2 University of Technology and Göteborg University, S-412 96 Göteborg, SWEDEN 3 Abteilung Halbleiterphysik, Universität Ulm, 89081 Ulm, GERMANY 4 Physikalisches Institut der Universität Würzburg, D-97074 Würzburg, GERMANY ABSTRACT Stressor-controlled epitaxy has been proposed as an efficient method of CdSe quantum dot fabrication. The studies are performed on a type-II CdSe/BeTe system, where CdTe and BeSe inteface bonds play a role of intrinsic stressors. Predeposition of ~0.2 ML CdTe stressor (∆a/a= +15%), corresponding to a local maximum of RHEED specular spot intensity, appears to induce variation of stress field across the BeTe surface, caused by alternating regions with CdTe and BeSe bonds. It results in preferential nucleation of regularly arranged CdSe QDs at the BeSe sites with the following vertical chess-ordering in the CdSe/BeTe multilayers. The structures demonstrate bright up to RT PL in the 1.9-2.1 eV range and strong in-plane PL anisotropy related to non-equivalent bottom and top CdSe QD interfaces having estimated from x-ray diffraction total concentrations of CdTe and BeSe bonds of 0.3-0.4 and 0.6-0.7 ML, respectively. INTRODUCTION In spite of the great efforts of numerous research groups to fabricate real self-organized CdSe quantum dots (QDs) having well defined interfaces, uniform lateral sizes below 5 nm, and being optically active up to room temperature, the problem is still far from solution. Therefore, looking for new approaches to controllable fabrication of real II-VI QDs is of great importance. The main idea of the novel technique developed and presented in this paper is an intentional introduction of a super-strained fractional monolayer (FM) of a much stronger lattice-mismatch compound – stressor –deposited just before the deposition of the QD material. Accumulating much larger stress than the QD material, the FM stressor should form on the matrix surface coherent islands with smaller both lateral sizes and inter-island distance, as it follows from continuum elasticity theory [1], thus creating strong local stress fields across the matrix surface, which would govern the QD formation. Recently, a stimulating effect of a BeSe FM “stressor” (∆a/a~-10%) on the self-formation of CdSe QDs in ZnSe has been observed, resulting in QDs arising even in a sub-monolayer CdSe thickness range, as displayed by transmission electron microscopy (TEM), µ-photoluminescence (µ-PL), and x-ray reflectometry [2]. In this paper the study of the stressor effect is performed on MBE grown type-II CdSe/BeTe nanostructures of no-common-atom binaries with nearly the same lattice mismatch (∆a/a~7.8%) as for the CdSe/ZnSe [3]. Although either BeSe (∆a/a~-10% for BeSe/BeTe) or CdTe (∆a/a ~14% for CdTe/BeTe) interface bon
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