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Self-Assembled InGaAs Quantum Dot Clusters with Controlled Spatial and Spectral Properties
Creasey, Megan,Lee, Ji-Hoon,Wang, Zhiming,Salamo, Gregory J.,Li, Xiaoqin American Chemical Society 2012 Nano letters Vol.12 No.10
<P>Planar quantum dot clusters (QDCs) consisting of six InGaAs quantum dots (QDs) formed around a GaAs nanomound are the most sophisticated self-assembled QDCs grown by molecular beam epitaxy thus far. We present the first photoluminescence measurements on individual hexa-QDCs with high spatial, spectral, and temporal resolution. In the best QDCs, the excitons confined in individual QDs are remarkably close in energy, exhibiting only a 10 meV spread. In addition, a biexponential decay profile and small variation in decay rates for different QDs was observed. The homogeneous energetics and dynamics suggest that the sizes, shapes, and composition of the QDs within these clusters are highly uniform.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2012/nalefd.2012.12.issue-10/nl3021736/production/images/medium/nl-2012-021736_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl3021736'>ACS Electronic Supporting Info</A></P>
Various Quantum- and Nano-Structures by III–V Droplet Epitaxy on GaAs Substrates
Lee, JH,Wang, Zh M,Kim, ES,Kim, NY,Park, SH,Salamo, GJ Springer 2010 NANOSCALE RESEARCH LETTERS Vol.5 No.2
<P>We report on various self-assembled In(Ga)As nanostructures by droplet epitaxy on GaAs substrates using molecular beam epitaxy. Depending on the growth condition and index of surfaces, various nanostructures can be fabricated: quantum dots (QDs), ring-like and holed-triangular nanostructures. At near room temperatures, by limiting surface diffusion of adatoms, the size of In droplets suitable for quantum confinement can be fabricated and thus InAs QDs are demonstrated on GaAs (100) surface. On the other hand, at relatively higher substrate temperatures, by enhancing the surface migrations of In adatoms, super lower density of InGaAs ring-shaped nanostructures can be fabricated on GaAs (100). Under an identical growth condition, holed-triangular InGaAs nanostructures can be fabricated on GaAs type-A surfaces, while ring-shaped nanostructures are formed on GaAs (100). The formation mechanism of various nanostructures can be understood in terms of intermixing, surface diffusion, and surface reconstruction.</P>
Size and density control of In droplets at near room temperatures
Lee, J H,Wang, Zh M,Kim, N Y,Salamo, G J IOP Pub 2009 Nanotechnology Vol.20 No.28
<P>We report on the ability to control the size and density of In droplets on GaAs(100) substrates at near room temperatures using solid source molecular beam epitaxy. We specifically demonstrate the height, diameter and density control of In droplets as functions of substrate temperature (<I>T</I><SUB>sub</SUB>) and monolayer (ML) coverage. For a range of density (∼10<SUP>9</SUP>–10<SUP>10</SUP> cm<SUP>−2</SUP>), the growth window is revealed to be between 20 and 70 °C. For a fixed ML coverage, the size and density of droplets can be controlled by controlling the <I>T</I><SUB>sub</SUB>. For a fixed <I>T</I><SUB>sub</SUB>, by controlling the ML coverage, droplet size and density can be controlled. Even at near room temperatures (20–70 °C), In atoms are extremely sensitive to surface diffusion and this enables the control of the size and density of droplets. This study provides an aid to understanding the formation of In droplets at near room temperatures and can find applications in the formation of quantum structures and/or nanostructures based on droplet epitaxy.</P>
Origin of nanohole formation by etching based on droplet epitaxy
Li, X.,Wu, J.,Wang, Z.,Liang, B.,Lee, J.,Kim, E. S.,Salamo, G. Royal Society of Chemistry 2014 Nanoscale Vol.6 No.5
Creating and manipulating materials at the nanoscale with controllable size, shape and nucleation site is an important task to meet the urgent demands for quantum structures with designed properties. In the last ten years, droplet epitaxy has been emerging as a versatile fabrication method for various complex nanostructures, such as quantum dots, quantum rings, double-rings, and so on. However, there is a lack of understanding of the deep nanohole formation based on droplet epitaxy at a high substrate temperature. Here we fabricate self-organized GaAs nanoholes by Ga droplet etching at high temperature based on droplet epitaxy, and they present good optoelectronic properties and have promising applications in fabrication of nanodevices due to their unique topology. A theoretical model is correspondingly proposed to explain the basic mechanism and simulate the time evolution of the nanohole structures. Our analysis shows that the morphology of the nanohole nanostructures can be well controlled through regulating experimental conditions.
Jihoon Lee,Wang, Z M,Eun-Soo Kim,Nam-Young Kim,Seung-Hyun Park,Salamo, G J IEEE 2011 IEEE TRANSACTIONS ON NANOTECHNOLOGY Vol.10 No.3
<P>The evolution of self-assembled InGaAs tandem nanostructures consisting a hole and pyramid is demonstrated using droplet epitaxy on various type-A high-index GaAs surfaces: (3 1 1)A (4 1 1)A, (5 1 1)A and (7 1 1)A. Under an identical fabrication condition depending on the index of surfaces, the resulting density and size of nanostructures are characteristic. The variation of density and size of nanostructures is explained with the relationship of the density of monolayer steps. An empirical model that describes the mechanism of self-assembled tandem nanostructures consisting a hole and pyramid is suggested as the concurrent occurrence of intermixing between droplets and substrate, dissolution of substrate and anisotropic surface diffusion.</P>
Effects of rapid thermal annealing on the optical properties of strain-free quantum ring solar cells
Wu, Jiang,Wang, Zhiming M,Dorogan, Vitaliy G,Li, Shibin,Lee, Jihoon,Mazur, Yuriy I,Kim, Eun Soo,Salamo, Gregory J Springer 2013 Nanoscale research letters Vol.8 No.1
<P>Strain-free GaAs/Al<SUB>0.33</SUB>Ga<SUB>0.67</SUB>As quantum rings are fabricated by droplet epitaxy. Both photoresponse and photoluminescence spectra confirm optical transitions in quantum rings, suggesting that droplet epitaxial nanomaterials are applicable to intermediate band solar cells. The effects of post-growth annealing on the quantum ring solar cells are investigated, and the optical properties of the solar cells with and without thermal treatment are characterized by photoluminescence technique. Rapid thermal annealing treatment has resulted in the significant improvement of material quality, which can be served as a standard process for quantum structure solar cells grown by droplet epitaxy.</P>