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Quantum Structures (quantum + structure)

Distribution by Scientific Domains
Physics and Astronomy85%

Selected Abstracts

Imaging of quantum array structures with coherent and partially coherent diffraction

JOURNAL OF SYNCHROTRON RADIATION, Issue 6 2003
I. A. Vartanyants
Recent achievements in experimental and computational methods open the possibility of measuring and inverting the diffraction pattern from a finite object of submicrometer size. In this paper the possibilities of such experiments for two-dimensional arrays of quantum dots are discussed. The diffraction pattern corresponding to coherent and partial coherent illumination of a sample was generated. Test calculations based on the iterative algorithms were applied to reconstruct the shape of the individual islands in such a quantum structure directly from its diffraction pattern. It is demonstrated that, in the case of coherent illumination, the correct shape and orientation of an individual island can be obtained. In the case of partially coherent illumination, the correct shape of the particle can be obtained only when the coherence of the incoming beam is reduced to match the size of the island. [source]

Nitride-based quantum structures and devices on modified GaN substrates

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2009
Piotr Perlin
Abstract We have studied the properties of InGaN layers and quantum wells grown on gallium nitride substrates with intentional surface misorientation with respect to its crystalline c -axis. Misorientation varied in the range from 0 up to 2 degree. The indium content was changed by using the different growth temperature (between 750 °C and 820 °C) during metalorganic vapor phase epitaxy. With increasing misorientation angle the average indium content decreased significantly. This effect was accompanied by the strong increase of the emission line bandwidth suggesting more pronounced indium segregation. The results of cathodoluminescence measurements show that these effects correspond to different number of atomic steps/terraces existing on the surface of gallium nitride substrate. Very interesting result is also demonstrated concerning p-type GaN layers. With increasing misorientation, the free hole density drastically increases above 1018 cm,3. This improvement in p-type doping is not related to the increased Mg concentration but to the reduction in the compensating donor density. Using this advantage we demonstrate nitride light emitters with improved electrical properties. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

TEM investigations of (In,Ga)N/GaN quantum structures

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2008
P. Manolaki
Abstract The paper reports on the influence of the growth temperature on the structural and chemical properties of (In,Ga)N quantum wells (QWs) on GaN. Two different samples A and B were fabricated. The QWs of the sample A were grown at a constant temperature of 600 °C. For the QWs of the sample B the temperature was 530 °C, while for the GaN barrier it was raised to 600 °C. The chemical and structural properties were studied by electron diffraction contrast imaging using the 0001 and 0002 reflection, respectively. Sample A exhibits homogeneous (In,Ga)N QWs. For sample B some undulated strain contrast of the QWs is visible hinting to the formation of quantum dots (QDs). The self-organisation of (In,Ga)N QDs in sample B is also evidenced by composition sensitive STEM-HAADF imaging, where the individual (In,Ga)N layers exhibit inhomogeneous intensity as well as varied thickness. Moreover, energy dispersive X-ray spectroscopy yielded enrichment of indium at QD sites. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Exciton-spin relaxation in weakly confining quantum dots due to spin,orbit interaction

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2006
E. Tsitsishvili
Abstract In weakly confining quantum structures such as interfacial islands or quantum disks the exciton-spin relaxation is governed by two independent electron and hole spin flip processes between the optically active and dark states. A microscopic theory for these transitions is presented which is based on second order spin,orbit and carrier,phonon interaction processes. We found that the sequential relaxation between bright and dark states leads to much faster exciton-spin relaxation than for strongly confining ("small") quantum dots where the dominant process stems from electron,hole exchange interaction plus hole deformation potential coupling. In addition, the fast exciton spin relaxation implies that the (exciton-bound) electron spin flip time is also much shorter than for a single electron. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Phase effects in HgTe quantum structures

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2007
M. König
Abstract HgTe quantum well structures with high electron mobilities have been used to fabricate quantum interference devices. Aharonov-Bohm oscillations have been studied in the low and high magnetic field regime. In the latter case a decrease of the effective ring radius is observed. Additionally, as a consequence of the strong Rashba spin-orbit coupling within this material, it was possible to observe conductance oscillations which are due to the so-called Aharonov-Casher effect. These quantum interference effects are effectively controlled by the applied magnetic and electric field. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Preface: phys. stat. sol. (c) 1/10

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2004
Eun-Kyung Suh
The Fifth International Symposium on Blue Laser and Light Emitting Diodes (ISBLLED-2004) was held in Gyeongju, Korea from 15,19 March 2004. Gyeongju, the ancient capital of the thousand-year Silla kingdom (57 B.C. to 935 A.D.) provided additional pleasure to the participants as an exceptional open-air museum with antique treasures scattered all around the city. During the last decade we have witnessed remarkable developments in wide-gap semiconductors and light emitting devices in the spectral range from the visible to deep UV. The purpose of the Symposium was to provide a forum for intensive discussion on the issues and main progress especially in optoelectronic devices, material growth and characterization, and quantum structures of wide bandgap semiconductors. A total of 243 papers including 220 contributed and 23 invited ones were presented and discussed by 487 participants from 17 countries world-wide. Among them, 154 manuscripts were submitted and reviewed by the usual evaluation process of physica status solidi. Some were rejected or withdrawn, and finally 139 papers are published in the special issues of physica status solidi (a), (b), and (c). We gratefully acknowledge the referees for their careful review. The papers are grouped into 7 categories. The subheadings and the number of papers in each are as follows: Optoelectronic devices, 43; Growth and characterization, 45; Nano and quantum structures, 21; Contacts, 8; Zinc oxide, 9; Indium nitride and indium rich InGaN, 6; Others, 7. The special session of the Symposium, "The LED Highlight", designed partially to meet the challenging targets of the technology, i.e., energy savings and clean environment preservation, drew much attention and is edited as a special coloured section in this issue. The next symposium is scheduled for Montpellier, France, in 2006. We wish the organizers of that symposium the best of luck and hope to see all of the ISBLLED-2004 participants again at ISBLLED-2006. ISBLLED-2004 was sponsored by The Research Society for the Wide-gap Semiconductors, Korean Physical Society, Office of Naval Research, Korea Science and Engineering Foundation, Korea Research Foundation, Korea Association for Photonics Industry Development, Asian Office of Aerospace Research and Development, and Korea Photonics Technology Institute. We would like to thank Ms. E. S. Hwang for her devotion to the preparation and the Proceedings of the symposium including the manuscript handling for publication. [source]

GaN-free transparent structure for ultraviolet light emitting diodes

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2004
T. Nishida
Abstract AlGaN-based light emitting diodes (LEDs) are expected to be the next generation of ultraviolet light (UV) sources. With the aim of achieving AlGaN-based UV-LEDs comparable to those of conventional blue and red LEDs, we have investigated the regular epitaxial growth, the fabrication of uniform and abrupt heterointerfaces, the optical characteristics of AlGaN-based nitride quantum structures, the validity of the band engineering, the p-n junction designs, radiative recombination and light extraction. Efficient and transparent UV-LEDs grown on a high-quality AlN-template layer on a sapphire substrate are free from binary GaN, and have great potential for lighting equipment and other applications. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]