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Nemcsics A.,Research Institute for Technical Physics and Materials Science | Nemcsics A.,H+ Technology | Toth L.,Research Institute for Technical Physics and Materials Science | Dobos L.,Research Institute for Technical Physics and Materials Science | Stemmann A.,Institute For Angewandte Physik Und Zentrum For Mikrostrukturforschung
Microelectronics Reliability | Year: 2011

In this work, droplet epitaxially grown GaAs quantum dots on AlGaAs surface are studied. The quantum dots are investigated in situ with RHEED and ex situ with TEM method. The TEM picture shows that the quantum dot is perfectly crystalline and fits very well to the crystal structure of the substrate. Furthermore, the side of the quantum dot shows stepped facet shape. Here, we show, how the stepped side shape forms from the droplet during crystallization. The RHEED picture shows broadened chevron-tail, which can be explained by the shape of the quantum dot. © 2011 Elsevier Ltd. All rights reserved. Source


Nemcsics A.,H+ Technology | Nemcsics A.,Research Institute for Technical Physics and Materials Science | Tth L.,Research Institute for Technical Physics and Materials Science | Dobos L.,Research Institute for Technical Physics and Materials Science | And 5 more authors.
Superlattices and Microstructures | Year: 2010

Self-assembled strain-free quantum dot (QD) structures were grown on AlGaAs surface by the droplet epitaxal method. The QDs were developed from pure Ga droplets under As pressure. The QDs were investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Both techniques show that the QDs are very uniform in size and their distribution on the surface is also homogeneous. The high resolution cross-sectional TEM investigation shows perfect lattice matching between the QD and the substrate, and also the faceting of the side walls of QD can be identified exactly by lattice planes. Analytical TEM (elemental mapping by EELS) unambiguously identifies the presence of Al in the QD. © 2010 Elsevier Ltd. All rights reserved. Source


Nemcsics A.,Research Institute for Technical Physics and Materials Science | Nemcsics A.,H+ Technology | Heyn C.,Institute For Angewandte Physik Und Zentrum For Mikrostrukturforschung | Toth L.,Research Institute for Technical Physics and Materials Science | And 3 more authors.
Journal of Crystal Growth | Year: 2011

We investigate strain-free GaAs quantum dots (QDs) fabricated by filling of nanoholes in semiconductor surfaces. The nanoholes are created in a self-organized fashion by local droplet etching with Al droplets as etchants. High resolution transmission electron microscopy (TEM) demonstrates that the quantum dots are free of extended defects. Elemental mapping using local electron energy loss spectroscopy (EELS) shows that the walls surrounding the nanohole openings consist of AlAs. This result confirms that the walls are optically inactive. © 2011 Elsevier B.V. All Rights Reserved. Source


Nemcsics A.,Obuda University | Nemcsics A.,Hungarian Academy of Sciences | Balazs J.,Hungarian Academy of Sciences | Podor B.,Obuda University | And 3 more authors.
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2011

Recently, the growth of self-assembled quantum structures has been intensively investigated for basics physics and device application. In our work, self-assembled strain-free GaAs quantum dots and quantum rings were investigated by the photoluminescence technique. The GaAs nanostructures are fabricated on AlGaAs (001) surface by droplet epitaxy method. Temperature dependent photoluminescence spectra were measured in the range of room temperature and 4 K. We give an explanation on the broadening of the photoluminescence peaks for different quantum structures. The calculated electronic structure is compared with the photoluminescence data. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Heyn C.,Institute For Angewandte Physik Und Zentrum For Mikrostrukturforschung | Schnull S.,Institute For Angewandte Physik Und Zentrum For Mikrostrukturforschung | Jesson D.E.,University of Cardiff | Hansen W.,Institute For Angewandte Physik Und Zentrum For Mikrostrukturforschung
Nanoscale Research Letters | Year: 2014

We describe a method to control the shape of nanoholes in GaAs (001) which combines the technique of local droplet etching using Ga droplets with long-time thermal annealing. The cone-like shape of inverted nanoholes formed by droplet etching is transformed during long-time annealing into widened holes with flat bottoms and reduced depth. This is qualitatively understood using a simplified model of mass transport incorporating surface diffusion and evaporation. The hole diameter can be thermally controlled by varying the annealing time or annealing temperature which provides a method for tuning template morphology for subsequent nanostructure nucleation. We also demonstrate the integration of the combined droplet/thermal etching process with heteroepitaxy by the thermal control of hole depth in AlGaAs layers. © 2014 Heyn et al.; licensee Springer. Source

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