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Advanced Quantum-Nano Materials & Optoelectronics Laboratory
 
 

QR code_Prof. Jihoon Lee

Kwangwoon Univ. KOR ver website

Kwangwoon Univ. Eng ver website

Kwangwoon College of Electronics and Informattion Engineering

Dept. of Electronics and Communications Engineering

 

University of Arkansas


Sam M. Walton College of Business

 

ERC 선도연구센터

BK 21 PLUS

Engineering Research Center, Holo-Digilog Human Media

Ministry of Science, ICT and Future Planning

Ministry Of Education

NIPA

KCC

Ministry of Education, Science and Technology

ITRC logo

ITRC Forum 2011

 

 

- Journal Editor -

3D Research

NRL cover

 

 

- Research Highlight -

 

Journal Cover: Precise Control of Configuration, Size and Density of Self-assembled Au Nanostructures on 4H-SiC (0001) by Systematic Variation of Deposition Amount, Annealing Temperature and Duration

(Journal cover,
CrystEngComm)
Volume 18
Issue 19

(2016)

Journal cover,CrystEngComm Volume 16 Issue 21 (2014)

(Journal cover,
CrystEngComm)
Volume 16
Issue 21

(2014)

 

Physica Status Solidi (a)) Volume 209 issue 6

(Journal cover,
Physica Status Solidi (a))
Volume 209
Issue 6

(2012)

 

Journal cover, Physica Status Solidi (a) Volume 208 Issue 1 (2011)

(Journal cover,
Physica Status Solidi (a))
Volume 208
Issue 1

(2011)

 

( Journal cover, IEEE Transactions on Nanotechnology) Volume 9 Issue 2  (2010)
( Journal cover,
IEEE Transactions on Nanotechnology)
Volume 9
Issue 2

(2010)

 

Wiley's Material Science online portal, Materials Views

(Materials Views, Wiley's Material Science)
"Nano Rings and Nano Pyramids"
(2010)

 


(Journal cover, Physica Status Solidi (a)) Volume 207 Issue 2  (2010)
(Journal cover,
Physica Status Solidi (a))
Volume 207
Issue 2

(2010)

 

(Journal cover, Applied Physics Letters) Volume 89 Issue 20  (2006)
(Journal cover,
Applied Physics Letters)
Volume 89
Issue 20

(2006)

 



(2006 MRS Fall Meeting Scene)
"Self-Assembly of InGaAs Quantum Dot Molecules (QDMs)"
(2006)

 

(Journal cover, Applied Physics Letters) Volume 88 Issue 23  (2006)

(Journal cover,
Applied Physics Letters)
Volume 88
Issue 23

(2006)

 

www.nanowerk.com

(NanoWerk, Spotlight)
"Quantum dot necklaces and other QD chains"
(April 12, 2006)

 

 


- PUBLICATIONS -

Journal Papers


* AUTHORS (in the order of authorship)
** TYPE: A: article, B: full book, CB: chapter of book, E: editor, & R: review, V: Video journal
***
IF: ISI® impact factor
*** Trend of Impact Factor of journals with interest (JCR IF 2015
)

 

TITLE: Self-Assembly of Multiple Stacked Nanorings by Vertically Correlated Droplet Epitaxy
AUTHORS:
J. Wu, Y. Hirono, X. Li, Z. M. Wang, J. H. Lee, M. Benamara, S. Luo, Y. I. Mazur, E. S. Kim, and G. J. Salamo
JOURNAL/BOOK TITLE: Advanced Functional Materials
VOLUME:  24                                FIRST PAGE: 530
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 10.439


Abstract


 

Fabrication of advanced artificial nanomaterials is a long-term pursuit to fulfill the promises of nanomaterials. In the last ten years, Droplet Epitaxy has been emerging as a versatile fabrication method for various complex nanomaterials, but there is a lack of growth protocol to control the growth vertically. Here we report a vertically correlated Droplet Epitaxy growth method. We find that the nanodroplets form preferable on the preexisting nanorings, which enables fabrication of vertically aligned nanostructures by Droplet Epitaxy. Nucleation thermodynamics and growth kinetics have been proposed to explain the vertically correlated Droplet Epitaxy. Heterojunctions can be realized at nanoscale by the presented method. In addition, the nucleation thermodynamics of nanodroplets observed in this article will allow site-controlled fabrication of nanostructures.

 


Graphical Abstract



Self-Assembly of Multiple Stacked Nanorings by Vertically Correlated Droplet Epitaxy

Self-Assembly of Multiple Stacked Nanorings by Vertically Correlated Droplet Epitaxy

Self-Assembly of Multiple Stacked Nanorings by Vertically Correlated Droplet Epitaxy

 

TITLE: Origin of nanohole formation by etching based on droplet epitaxy
AUTHORS:X. Li, J. Wu, Z. M. Wang, B. Liang, J. H. Lee, E. S. Kim, and G. J. Salamo
JOURNAL/BOOK TITLE: Nanoscale
VOLUME: 6                                 FIRST PAGE: 2675
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 6.739   

Abstract



 

The self-organized GaAs nanoholes are fabricated by Ga droplet etching based on droplet epitaxy. A theoretical model is proposed to explain the basic mechanism behind droplet etching. With this model, it is possible to directly simulate the time evolution of nanohole structures. Our analysis shows that the morphology of the holed nanostructures can be controlled through regulating experimental conditions. For instance, high etching rate, high number density of droplets, large size of droplet, or low intensity of As flux can increase the depth of hole. The results based on the proposed model are in good agreement with experimental observations.

 


Graphical Abstract



Origin of nanohole formation by etching based on droplet epitaxy

Origin of nanohole formation by etching based on droplet epitaxy



TITLE: Droplets to Merged Nanostructures: Evolution of Gold Nanostructures by the Variation of Deposition Amount on Si(111)
AUTHORS: M. Y. Li, M. Sui, E. S. Kim
and J. H. Lee
JOURNAL/BOOK TITLE: Crystal Growth & Design
VOLUME: 14                                 FIRST PAGE: 1128
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 4.558 


Abstract


 

We studied the evolution of Au nanostructures in dome-shaped Au droplets that merge into Au nanostructures on Si (111) by systematically controlling the Au deposition amount (DA) under a fixed annealing temperature and annealing duration. Even under identical growth conditions, the configuration, density, and size of Au nanostructures drastically vary depending on the amount of Au deposition in the range of 0.5 - 20 nm. Through systematic analysis of the resulting Au nanostructures in determining the average height, density, and surface area ratio, as well as the Fourier filter transform power spectrum and cross-sectional line-profiles, we clearly demonstrate the evolution process of Au nanostructures and thus the control of the size, density, and configurations. The evolution of Au droplets on Si (111) with the increased DAs initially appears to be progressing based on the Volmer–Weber growth mode for the Au DAs up to 4 nm, but with further increased DAs up to 20 nm, it turns out that the growth occurs in the Frank – van der Merwe growth mode, resulting in a layer-by-layer growth. In addition, by the sharp comparison between pre-annealed samples and resulting Au nanostructures, we quantitatively present the evolution of Au nanostructures. This study can find applications in the nanowire fabrication on Si (111).

 

Graphical Abstract



Evolution of Gold Nanostructures by the Variation of Deposition Amount on Si (111): Droplets to Merged Nanostructures
Evolution of Gold Nanostructures by the Variation of Deposition Amount on Si (111): Droplets to Merged Nanostructures

 

TITLE: Fabrication of self-assembled Au droplets by systematic variation of deposition amount on various type-B GaAs surfaces
AUTHORS: M. Sui, M. Y. Li, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
Nanoscale Research Letters
VOLUME: 9                                 FIRST PAGE:
436
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 2.481


Abstract


 

The fabrication of self-assembled Au droplets is successfully demonstrated on various GaAs (n11)B, where n is 2, 4, 5, 7, 8 and 9, by the systematic variation of Au deposition amount (DA) from 2 to 12 nm. Under an identical growth condition, the self-assembled Au droplets of mini to super-sizes are successfully synthesized via the Volmer-Weber growth mode. Depending on the DA, an apparent evolution trend is clearly observed in terms of the average height (AH), lateral diameter (LD) and average density (AD). For example, as compared with the mini Au droplets with the DA of 2 nm: AH 22.5 nm and LD 86.5 nm, the super-sized Au droplets show significantly increased AH by 316% and LD by 320% with 12 nm DA reaching AH: 71.1 and LD: 276.8 nm on GaAs (211)B. In addition, accompanied with the dimensional expansion, the AD of Au droplets drastically swings on the two orders of magnitudes between 3.2 × 10^10 and 4.2 × 10^8 cm^-2. The results are systematically analyzed in aspects of the AFM and SEM images, EDS spectra, cross-sectional line-profiles, FFT power spectra and root mean squared (RMS) roughness as well as the droplet dimension and density summary respectively.

 

Graphical Abstract



Fabrication of self-assembled Au droplets by systematic variation of deposition amount on various type-B GaAs surfaces

Fabrication of self-assembled Au droplets by systematic variation of deposition amount on various type-B GaAs surfaces

 

 

TITLE: Mini Droplets to Super Droplets: Evolution of Self-Assembled Au droplets on GaAs (111)B and (110)
AUTHORS: M. Sui, M. Y. Li, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE: Journal of Applied Crystallography
VOLUME: 
47                                 FIRST PAGE: 505-510
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 3.95   


Abstract


 

In this article, the effect of deposition amount on self-assembled Au droplets fabricated on GaAs(111)B and (110) is presented. The investigation is systematically performed by the variation of the Au deposition amount from 2 to 20 nm while fixing the other growth parameters such as annealing temperature and duration to clearly observe the effect. Under identical growth conditions, the self-assembled Au droplets show significantly different size and density depending on the amount of Au deposition: i.e. the average height varies by 436% from 21.8 to 95.5 nm and the average diameter swings by 827% from 52 to 430 nm, showing that the size increase is dominated by the lateral expansion. Meanwhile the average density varies by over two orders of magnitude from 1.24 × 108 to 4.48 × 1010 cm-2 on GaAs(111)B. With relatively low Au deposi­tion amounts, below 3 nm, round dome-shaped mini Au droplets with high packing density can be fabricated, while super large Au droplets result with higher deposition amounts, above 10 nm, with a density two orders of magnitude lower. It is also found that the surface index has a minor effect on the fabrication of self-assembled Au droplets with the variation of deposition amount. The results are systematically analyzed and discussed in terms of atomic force microscopy and scanning electron microscopy images, line profiles, power spectrums, r.m.s. surface roughness, and size and density plots.

 

Graphical Abstract



Mini Droplets to Super Droplets: Evolution of Self-Assembled Au droplets on GaAs (111)B and (110)
Mini Droplets to Super Droplets: Evolution of Self-Assembled Au droplets on GaAs (111)B and (110)
Mini Droplets to Super Droplets: Evolution of Self-Assembled Au droplets on GaAs (111)B and (110)
Mini Droplets to Super Droplets: Evolution of Self-Assembled Au droplets on GaAs (111)B and (110)

 

 

TITLE: Annealing Temperature Effect on the Fabrication of Self-assembled Gold Droplets on various Type-B GaAs Surfaces
AUTHORS: M. Sui, M. Y. Li, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
CrystEngComm
VOLUME:  16                                 FIRST PAGE: 4390
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 3.858


Abstract


 

In this paper, the fabrication and detailed evolution process of the self-assembled Au droplets are successful demonstrated on diverse GaAs type-B (n11) substrates, where n is 9, 7, 5, 4, and 2. The evolution process is systematically investigated by the variation of the annealing temperature (Ta) from 250 to 550 °C. Self-assembled Au clusters begin to nucleate at 300 °C as a nucleation stage and wiggly nanostructures with the connected geometry are resulted at 350 °C as a transitional stage. Between 400 and 550 °C, the self-assembled Au droplets are successful fabricated and they show the increased average dimensions along with the decreased density as a function of the Ta while showing the improved size uniformity above 500 °C. Depending on the substrates utilized, the resulting Au droplets show the dependency on the index throughout the Ta range, which is systematically analyzed in relation to the RMS roughness.

 


Graphical Abstract



Annealing Temperature Effect on the Fabrication of Self-assembled Gold Droplets on various Type-B GaAs Surfaces

Annealing Temperature Effect on the Fabrication of Self-assembled Gold Droplets on various Type-B GaAs Surfaces

Annealing Temperature Effect on the Fabrication of Self-assembled Gold Droplets on various Type-B GaAs Surfaces

 

 


TITLE: Inside front cover: Annealing Temperature Effect on the Fabrication of Self-assembled Gold Droplets on various Type-B GaAs Surfaces (CrystEngComm, 2014,16, 4342-4342)
AUTHORS: M. Sui, M. Y. Li, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE: CrystEngComm
VOLUME:  16                                 FIRST PAGE: 4390
YEAR OF PUBLICATION: 2014                              KEY: A                      IF:
3.858
Journal cover
 
TITLE: Effect of deposition amount on the evolution of self-assembled Au droplets on GaAs (111)A and (100)
AUTHORS: M. Y. Li.
, M. Sui, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
Nanoscale Research Letters
VOLUME:                                  FIRST PAGE:
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 2.481


Abstract


 

In this paper, we report the effect of Au thickness on the self-assembled Au droplets on GaAs (111)A and (100). The evolution of Au droplets on GaAs (111)A and (100) with the increased Au thickness progress in the Volmer–Weber growth mode; results in distinctive 3-D islands. Under an identical growth condition, depending on the thickness of Au deposition, the self-assembled Au droplets show different size and density distributions, while the average height is increased by ~ 420% and the diameter is increased by ~ 830%, indicating a preferential lateral expansion. Au droplets show an opposite evolution trend; the increased size along with the decreased density as a function of the Au thickness and over the thickness range tested, the density shifts on the orders of over two magnitude between 4.23×1010 and 1.16×108 cm-2. At relatively thinner thicknesses below 4 nm, the self-assembled Au droplets sensitively respond to the thickness variation, evidenced by the sharper slopes of dimensions and density plots. The results are systematically analyzed and discussed in terms of atomic force microscope (AFM), scanning electron microscope (SEM), energy-dispersive x-ray spectroscopy (EDS), cross-sectional surface line-profiles and Fourier filter transform (FFT) power spectra.

 

Graphical Abstract



Effect of deposition amount on the evolution of self-assembled Au droplets on GaAs (111)A and (100)

Effect of deposition amount on the evolution of self-assembled Au droplets on GaAs (111)A and (100)

 

 

TITLE: Control of size and density of self-assembled Au droplets via systematic deposition amount control on high-index GaAs type-A surfaces
AUTHORS: M. Y. Li, M. Sui, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
Japanese Journal of Applied Physics
VOLUME:  53                                FIRST PAGE: 095502
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 1.057


Abstract


 

Au droplets as a catalyst can be used to determine the size, density, and configuration of nanowires (NWs) during crystallization at the liquid-solid interface, and the growth direction, cross-sectional shape, and even the quality of the NWs can be controlled by adjusting the substrate index utilized. In this study, the control of the size and density of self-assembled Au droplets is systematically demonstrated via the deposition amount (DA) control between 2 and 12 nm on various GaAs type-A substrates: (711)A, (511)A, (411)A, and (311)A. The self-assembled Au droplets are formed owing to the much higher binding energy between Au adatoms than the energy between Au atoms and substrate atoms based on the Volmer–Weber growth mode, and even up to 12 nm DA, the three-dimensional (3D) island phase (droplets) without coalescence is observed. Within the DA range, the self-assembled Au droplets sensitively respond to the DA variation, which results in over 3 times increment in dimensions along with the corresponding change in density on the two orders of magnitude from ~ 108 to ~1010. Depending on the index utilized, the high index effect is not obvious owing to weak binding energy between GaAs substrate and Au adatoms and the wide DA range. The results are systematically analyzed using atomic force microscope (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), cross-sectional line profiles, and Fourier filter transform (FFT) power spectra.

 

Graphical Abstract



Control of size and density of self-assembled Au droplets via systematic deposition amount control on high-index GaAs type-A surfaces

Control of size and density of self-assembled Au droplets via systematic deposition amount control on high-index GaAs type-A surfaces

 

 

TITLE: Nucleation, transition and maturing of the self-assembled Au droplets on various Type-A GaAs substrates
AUTHORS: M. Y. Li., M. Sui, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
Journal of Applied Physics
VOLUME: 116                                 FIRST PAGE: 084301
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 2.185


Abstract


 

In this study, the fabrication of self-assembled Au droplets is successfully demonstrated on various type-A GaAs substrates: (711)A, (511)A, (411)A, and (311)A. The nucleation of the self-assembled tiny Au clusters is observed at 300 oC. As an intermediate stage, corrugated Au nanostructures are clearly observed at 350 oC on various type-A GaAs surfaces, rarely witnessed on other substrates. Based on the Volmer-Weber growth mode, the dome-shaped Au droplets with excellent uniformities are successfully fabricated between 500 and 550 oC. As a function of annealing temperature, the self-assembled Au droplets show the increased dimensions including average height and diameter, compensated by the decreased average density. Depending on the substrate indices utilized, the size and density of Au droplets show clear differences throughout the whole temperature range. The results are symmetrically analyzed by using AFM images, cross-sectional line-profiles, size and density plots, height distribution histograms and FFT power spectra.

 

Graphical Abstract



Nucleation, transition and maturing of the self-assembled Au droplets on various Type-A GaAs substrates

Nucleation, transition and maturing of the self-assembled Au droplets on various Type-A GaAs substrates

Nucleation, transition and maturing of the self-assembled Au droplets on various Type-A GaAs substrates

 

 

TITLE: “From the Nucleation of Wiggling Au Nanostructures To the Dome Shaped Au Droplets on GaAs (111)A, (110), (100) and (111)B
AUTHORS:
M. Y. Li, M. Sui, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
Nanoscale Research Letters
VOLUME: 9                                 FIRST PAGE: 113
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 2.481


Abstract


 

In this paper, the systematic evolution process of self-assembled Au droplets is successfully demonstrated on GaAs (111)A, (110), (100), and (111)B. On various GaAs substrates, self-assembled Au clusters begin to nucleate at around 300 [degree sign]C, and then, they develop into wiggly Au nanostructures at 350 [degree sign]C. Between 400 [degree sign]C and 550 [degree sign]C, the self-assembled dome-shaped Au droplets with fine uniformity are fabricated with various sizes and densities based on the Volmer-Weber growth mode. Depending on the annealing temperature, the size including the average height and lateral diameter and the density of Au droplets show the opposite trend of increased size with correspondingly decreased density as a function of the annealing temperature due to the difference in the diffusion length of adatoms at varied activation energy. Under an identical growth condition, depending on the surface index, the size and density of Au droplets show a clear distinction, observed throughout the temperature range. The results are systematically analyzed and discussed in terms of atomic force microscopy (AFM) images, cross-sectional line profiles, and Fourier filter transform (FFT) power spectra as well as the summary plots of the size and density.

 

Graphical Abstract



From the Nucleation of Wiggling Au Nanostructures To the Dome Shaped Au Droplets on GaAs (111)A, (110), (100) and (111)B

From the Nucleation of Wiggling Au Nanostructures To the Dome Shaped Au Droplets on GaAs (111)A, (110), (100) and (111)B

From the Nucleation of Wiggling Au Nanostructures To the Dome Shaped Au Droplets on GaAs (111)A, (110), (100) and (111)B

 

 

 

TITLE: Coulomb interaction signatures in self-assembled lateral quantum dot molecules
AUTHORS: Xinran. R. Zhou, J. H.Lee, Gregory. J. Salamo, Miquel. Royo, Juan. I. Climente, and Matthew. F. Doty
JOURNAL/BOOK TITLE: Physical Review B
VOLUME: 87                                 FIRST PAGE: 125309
YEAR OF PUBLICATION:
2013                              KEY: A                      IF: 3.691

Abstract



 

We use photoluminescence spectroscopy to investigate the ground state of single self-assembled InGaAs lateral quantum dot molecules. We apply a voltage along the growth direction that allows us to control the total charge occupancy of the quantum dot molecule. Using a combination of computational modeling and experimental analysis, we assign the observed discrete spectral lines to specific charge distributions. We explain the dynamic processes that lead to these charge configurations through electrical injection and optical generation. Our systemic analysis provides evidence of inter-dot tunneling of electrons as predicted in previous theoretical work.

 


Graphical Abstract



Coulomb interaction signatures in self-assembled lateral quantum dot moleculesCoulomb interaction signatures in self-assembled lateral quantum dot molecules

Coulomb interaction signatures in self-assembled lateral quantum dot molecules

 

TITLE: Epitaxially Self-Assemblied Quantum Dot Pairs
AUTHORS: J. Wu, X. Hu, J. H. Lee, E
. S. Kim, Z. M. Wang
JOURNAL/BOOK TITLE: Advanced Optical Materials
VOLUME: 1(3)                                 FIRST PAGE: 201-
214
YEAR OF PUBLICATION:
2013                              KEY: A                       IF: 4.062

Abstract



 

The present paper reviews the recent efforts and achievements regarding the fabrication techniques of self-assembled quantum dot pairs. Quantum dot pairs, the simplest but most-investigated quantum dot molecules, have attracted significant attention due to their potential applications in quantum information technologies. In the last several decades, the development of epitaxial growth has advanced the design and control of how novel quantum dot pairs form at nanoscale. Both vertically and laterally aligned quantum dot pairs can be grown using the molecular beam epitaxy technique. In this review, we provide assess various growth methods of aligned quantum dot pairs fabricated by molecular beam epitaxy. We highlight the recent development of novel growth techniques and discuss the morphological, electrical, and optical properties of quantum dot pairs. Using advanced epitaxial growth techniques to fabricate well-controlled quantum dot pairs opens the door to developing of advanced quantum information technologies and understanding the unveiled physics and properties of artificial quantum molecules.

 


Graphical Abstract



Self-Assembly of Quantum Dot Pairs

Self-Assembly of Quantum Dot Pairs

Self-Assembly of Quantum Dot Pairs

 

TITLE: Effects of Rapid Thermal Annealing on the Optical Properties of Strain-Free Quantum Ring Solar Cells
AUTHORS:
J. Wu, Z. M. Wang, V. G. Dorogan, S. Li, J. H. Lee, Y. I. Mazur, E. S. Kim, and G. J. Salamo
JOURNAL/BOOK TITLE: Nanoscale Research Letters
VOLUME: 8                                 FIRST PAGE: 12
YEAR OF PUBLICATION:
2013                              KEY: A                      IF: 2.52

Abstract



 

Strain-free GaAs/Al0.33Ga0.67As 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.

 


Graphical Abstract



Optical Properties of Strain-Free Quantum Ring Solar Cells
Optical Properties of Strain-Free Quantum Ring Solar Cells
Optical Properties of Strain-Free Quantum Ring Solar Cells

 

 

TITLE: Self-Assembled InGaAs Quantum Dot Clusters with Controlled Spatial and Spectral Properties
AUTHORS: Megan Creasey, Ji-Hoon Lee, Zhi-Ming Wang, Gregory J. Salamo and
Xiaoqin Li
JOURNAL/BOOK TITLE:
Nano Letters
VOLUME: 12                                 FIRST PAGE: 5169–5174
YEAR OF PUBLICATION:
2012                              TYPE: A                      IF: 13.198

Abstract



 

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.

 


Graphical Abstract



Self-Assembled InGaAs Quantum Dot Clusters with Controlled Spatial and Spectral Properties

Self-Assembled InGaAs Quantum Dot Clusters with Controlled Spatial and Spectral Properties

Self-Assembled InGaAs Quantum Dot Clusters with Controlled Spatial and Spectral Properties

TITLE: Annealing temperature effect on self-assembled Au droplets on Si (111)
AUTHORS: M. Sui, M. Y. Li, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE: Nanoscale Research Letters
VOLUME: 8                                 FIRST PAGE: 525
YEAR OF PUBLICATION:
2013                              KEY: A                      IF: 2.52  


Abstract


 

We investigate the effects of annealing temperature on self-assembled Au droplets on Si (111) substrates. To achieve this, we systematically vary the annealing temperatures while fixing other growth environment. The annealing temperature is varied from 50 to 850 °C with 2 nm Au deposition. With increased annealing temperatures for a fixed thickness of deposition, the height and diameter of Au droplets shows a gradual increase while the density gradually decreases. The results are systematically analyzed in aspects of cross-sectional line-profiles, FFT power spectra, height histogram, surface area ratio, and droplet dimension & density analyses respectively.

 


Graphical Abstract



Effects of annealing temperature on self-assembled Au droplets on Si (111)

Effects of annealing temperature on self-assembled Au droplets on Si (111)

 

TITLE: Strain-Free Ring-Shaped Nanostructures by Droplet Epitaxy for Photovoltaic Application
AUTHORS: J.
Wu, Z. M. Wang, V. G. Dorogan, S. Li, Z. Zhou, H. Li, J. H. Lee, E. S. Kim, Y. I. Mazur, and G. J. Salamo
JOURNAL/BOOK TITLE: Applied Physics Letters
VOLUME: 101                                 FIRST PAGE: 043904
YEAR OF PUBLICATION:
2012                              TYPE: A                      IF: 3.844

Abstract



 

Droplet epitaxy is a flexible nanomaterial growth technique and is a potential method to fabricate advanced electronic and optoelectronic devices. Here, we report strain-free GaAs/Al0.33Ga0.67As quantum ring solar cells fabricated by droplet epitaxy technique. Photoluminescence is used to study the electronic structure of the lattice-matched GaAs/Al0.33Ga0.67As quantum ring solar cells. Post-growth thermal annealing is used to improve the optical quality of the solar cell as well as device efficiency. A power conversion efficiency of 1.8% is demonstrated from a prototype quantum ring solar cell. This work opens new opportunities for quantum dot solar cells with strainfree nanostructures.

 


Graphical Abstract



Strain-Free Ring-Shaped Nanostructures

Strain-Free Ring-Shaped Nanostructures

 

TITLE: Observation of Ga Metal Droplet Formation on Photo-lithographically Patterned GaAs (100) Surface by Droplet Epitaxy
AUTHORS: Lei Gao, Y. K. Hirono, M. Y. Li,
J. Wu, S. M. Song, S. M. Koo, E. S. Kim, Zh. M. Wang, J. H. Lee and G. J. Salamo
JOURNAL/BOOK TITLE: IEEE Transactions on Nanotechnology 
VOLUME:  11                                 FIRST PAGE: 985
YEAR OF PUBLICATION:
2012                             TYPE: A                      IF: 2.292

Abstract
 

A sharp contrast on the density and size of Ga metal droplets is observed on various photo-lithographically patterned GaAs (100). As clearly evidenced by high-resolution scanning electron microscope (HR-SEM), Ga metal droplet density and size surprisingly differ on etched and un-etched surfaces under an identical growth condition. The apparent contrast on the density and size of droplets is clearly observed at the interface between etched and un-etched areas. Ga droplets exhibit much higher density and the size is much smaller on etched surface meanwhile the density is an order of magnitude lower and the size is much larger on un-etched surface. Along different directions, [011] & [01-1], due to anisotropic surface diffusion the density is about twice higher along [011] for the same strip pattern.

 


Graphical Abstract



Observation of Ga Metal Droplet FormationObservation of Ga Metal Droplet Formation

 

TITLE: Critical Size of Self-Propelled Motion of Droplets on GaAs (100) Surface
AUTHORS: J. Wu, Z. M. Wang, A. Z. Li, M.
Benamara, J. H. Lee, S. D. Koukourinkova, E. S. Kim, G. J. Salamo
JOURNAL/BOOK TITLE: J
ournal of Applied Physics
VOLUME: 112                                 FIRST PAGE: 043523
YEAR OF PUBLICATION:
2012                              TYPE: A                      IF: 2.168

Abstract



 

The running liquid Ga droplets on GaAs surface (001) are presented and analyzed by scanning electron microscope and atomic force microscope. Self-motion of Ga droplet on GaAs surface is confirmed by microscope measurements. The liquid droplets are found to move with an initial critical diameter and constantly increase size during motion. The critical diameter of moving Ga droplets is observed to be 1.9 µm on GaAs (011) surface at preparation temperature 680 °C. A linear relationship is found between droplet diameter and trail length. These experiment results are qualitatively analyzed to understand the phenomenon of self-running Ga droplets on GaAs surface.

 


Graphical Abstract

Critical Size of Self-Propelled Motion

Critical Size of Self-Propelled Motion

 

TITLE: Increased Light Trapping by Surface Nano-structuring on Si using MWCNT mask etching technique
AUTHORS: M. Y. Hwang, M. Y. Li, H. S. Kim, E. S. Kim, J. H. Lee and S. M. Koo
JOURNAL/BOOK TITLE: Journal of Nanoelectronics and Optoelectronics
VOLUME: 7                                  FIRST PAGE: 311
YEAR OF PUBLICATION: 2012                                   TYPE: A                        IF:
0.90

Abstract



 


We demonstrate an increased light-trapping on Si using surface nano-structuring technique. For comparison, four samples are prepared using conventional photolithography and carbon nanotube etch-mask technique. With a bare-Si set as a reference, the square-patterned Si using conventional photolithography shows an improved average light-trapping by ~12 %. When multi-walled carbon nanotubes (MWCNT) dispersed in isopropyl-alcohol is used as a etch mask, the average light-trapping level is improved by ~22 %. The average light-trapping is increased to ~ 38 % with MWCNT etch-masked Si with HMDS dispersion. The increase in light trapping level is most significant in UV region and becomes less noteworthy as wavelength increases. The increased light-trapping can be due to increased surface roughness and thus area. This result can find applications where the light-trapping is vital such as photovoltaics, photo-diodes and photo-transistors.


 


Graphical Abstract



Increased Light Trapping by Surface Nano-structuring Increased Light Trapping by Surface Nano-structuring


 

TITLE: Formation of Ga droplets on patterned GaAs (100) by molecular beam epitaxy
AUTHORS: M. Y. Li, Y. K. Hirono, S. D. Koukourinkova, M. Sui, S. M. Song, E. S. Kim, J. H. Lee, and G. J. Salamo
JOURNAL/BOOK TITLE:
Nanoscale Research Letters
VOLUME: 7                                 FIRST PAGE: 550(1) 
YEAR OF PUBLICATION:
2012                             TYPE: A                      IF:2.73

Abstract



 

In this paper, the formation of Ga droplets on photo-lithographically patterned GaAs (100) and the control of the size and density of Ga droplets by droplet epitaxy using molecular beam epitaxy are demonstrated. In extension of our previous result from the journal Physical Status Solidi A, volume 209 in 2012, the sharp contrast of the size and density of Ga droplets is clearly observed by high-resolution scanning electron microscope, atomic force microscope, and energy dispersive X-ray spectrometry. Also, additional monolayer (ML) coverage is added to strength the result. The density of droplets is an order of magnitude higher on the trench area (etched area), while the size of droplets is much larger on the strip top area (un-etched area). A systematic variation of ML coverage results in an establishment of the control of size and density of Ga droplets. The cross-sectional line profile analysis and root mean square roughness analysis show that the trench area (etched area) is approximately six times rougher. The atomic surface roughness is suggested to be the main cause of the sharp contrast of the size and density of Ga droplets and is discussed in terms of surface diffusion.

 


Graphical Abstract



Control of Size and Density of Liquid Ga Metal Droplets

Control of Size and Density of Liquid Ga Metal Droplets


 

TITLE: Influence of Ga coverage on the sizes of GaAs quantum dash pairs grown by high temperature droplet epitaxy
AUTHORS: J. Wu, Zh. M. Wang, S. Li,
J. H. Lee, Y. I. Mazur and G. J. Salamo
JOURNAL/BOOK TITLE: Physica
Status Solidi (RRL) - Rapid Research Letters
VOLUME: 6                                 FIRST PAGE: 309
YEAR OF PUBLICATION:
2012                             TYPE: A                      IF:2.218

Abstract



 

We investigate the formation of GaAs quantum dot pairs with different by droplet epitaxy. The GaAs quantum dot pairs of various sizes are fabricated by high temperature droplet epitaxy. Dual-sized quantum dot pairs are observed along [01-1] orientation. Depending on the Ga coverage, the width of the quantum dot pairs can be tuned from ~100 nm to ~300 nm while keeping the height in the range of 4 nm to 10 nm. Very narrow PL spectrum with FWHM=4.3 nm is observed for QDPs with 13 ML Ga coverage.

 


Graphical Abstract



Influence of Ga coverage on the Sizes and Shapes
Influence of Ga coverage on the Sizes and Shapes

 

TITLE: Nanocrystalline GaZnO films for transparent electrode to silicon carbide
AUTHORS: J. H. Lee, J. H. Kim, K. M. Do, B. M. Moon, J. H. Lee and S. M. Koo
JOURNAL/BOOK TITLE: Journal of Nanoelectronics and Optoelectronics
VOLUME: 7                                 FIRST PAGE: 260
YEAR OF PUBLICATION:
2012                                   TYPE: A                      IF:0.90

Abstract



 


Nanocrystalline 2% Ga doped zinc oxide (GaZnO) thin films were epitaxially deposited on n-type 4H-SiC (0001) by a pulsed laser deposition (PLD) at different substrate temperatures of 250, 400, and 550 oC, respectively. Structural and electrical properties of nanocrystalline GaZnO thin film on 4H-SiC were investigated by using X-ray diffraction, atomic force microscopy (AFM), Hall effect measurement, transmission line method (TLM), and Auger electron spectroscopy (AES). The nanocrystalline GaZnO film deposited at 400 oC show the lowest resistivity of 3.3 x 10-4 Ω cm, and highly c-axis oriented crystalline quality with being sharper and higher diffraction angle, which result in. The specific contact resistance (ρc), measured from the Au/Ti/GaZnO/SiC of ~ 0.05 Ω cm2. The relative amount of activated Ga3+ ions was 2.02% in GaZnO film by AES measurement.


 


Graphical Abstract



Nanocrystalline GaZnO films

Nanocrystalline GaZnO films

Nanocrystalline GaZnO films


TITLE: Inside Back Cover: Sharp contrast of the density and size of Ga metal droplets on photolithographically patterned GaAs (100) by droplet epitaxy under an identical growth environment (Phys. Status Solidi A 6/2012)
AUTHORS: M. Y. Li, J. H. Lee, Zh. M. Wang, Y. K. Hirono, J. Wu, S. M. Song, S. M. Koo, E. S. Kim and G. J. Salamo
JOURNAL/BOOK TITLE: Physica Status Solidi (a)
VOLUME: 209                                  FIRST PAGE: 1075
YEAR OF PUBLICATION:
2012                             TYPE: A                      IF: 1.221
Sharp Contrast of the Density and Size of Ga Metal Droplets
 

 

TITLE: Sharp Contrast of the Density and Size of Ga Metal Droplets on Photolithographically Patterned GaAs (100) by Droplet Epitaxy under an Identical Growth Environment
AUTHORS: M. Y. Li, J. H. Lee, Zh. M. Wang, Y. K. Hirono, J. Wu, S. M. Song, S. M. Koo, E. S. Kim and G. J. Salamo
JOURNAL/BOOK TITLE: Physica Status Solidi (a)
VOLUME: 209                                  FIRST PAGE: 1075
YEAR OF PUBLICATION:
2012                             TYPE: A                      IF: 1.221

Abstract



 

A sharp contrast of the density and size of Ga metal droplets (MDs) on strip patterned GaAs (100) is demonstrated through droplet epitaxy (DE) and photolithography technique. As clearly evidenced by scanning electronic microscope (SEM) and atomic force microscope (AFM), MD density between etched (patterned) and un-etched (un-patterned) surfaces can be sharply different up to one order of magnitude under an identical growth condition. Etched surface exhibits much higher density and smaller diameter and height of MDs.

 


Graphical Abstract



Sharp contrast of the density and size of Ga metal dropletsSharp contrast of the density and size of Ga metal droplets

 

TITLE: Fabrication and characterization of ZnO film-based heterojunction diodes on 4H-SiC
AUTHORS: J. H. Kim, K. M. Do, J. W. Kim, J. C. Jung, J. H. Lee, B. M. Moon, and S. M. Koo
JOURNAL/BOOK TITLE: Journal of Nanoelectronics and Optoelectronics
VOLUME: 7                                 FIRST PAGE: 271
YEAR OF PUBLICATION: 2012                                   TYPE: A                      IF:
0.90

Abstract



 


Nanocrystalline n-ZnO/p-4H-SiC heterojunction diodes were successfully fabricated and characterized. The epitaxially grown ZnO films were obtained by using a pulsed laser deposition method. X-ray diffraction (XRD) pole figure analysis showed that the c-oriented ZnO films were grown on 4H-SiC (0001) substrates with in-plane orientation of ZnO [11-20 ]||4H-SiC [11-20 ], which is attributed to the small lattice mismatch of ZnO with 4H-SiC (~5.5%). The ZnO films with nano-sized grains were confirmed by surface morphology analysis. In order to investigate the electrical properties, the Ohmic contact electrodes were formed directly onto the ZnO and 4H-SiC surfaces. Current-voltage characteristics of the heterojunction diodes had a good rectifying behavior with an on/off ratio above 108. The current transport mechanisms in different bias regions were also discussed


 


Graphical Abstract



Fabrication and characterization of ZnO film
Fabrication and characterization of ZnO film

 

TITLE: Spectroscopic signatures of many-body interactions and delocalized states in self-assembled lateral quantum dot molecules
AUTHORS: X. Zhou, S. Sanwlani, W. Liu, J. H. Lee, Zh. M. Wang, G. Salamo, and M. F. Doty
JOURNAL/BOOK TITLE: Physical Review B
VOLUME: 84                                 FIRST PAGE: 205411
YEAR OF PUBLICATION:
2011                              TYPE: A                      IF: 3.772

(Selected by the editors of PRB to be an Editor's Suggestion: Highlighed Articles)


Abstract



 

Lateral quantum dot molecules consist of at least two closely spaced InGaAs quantum dots arranged such that the axis connecting the quantum dots is perpendicular to the growth direction. These quantum dot complexes are called molecules because the small spacing between the quantum dots is expected to lead to the formation of molecular-like delocalized states.We present optical spectroscopy of ensembles and individual lateral quantum dot molecules as a function of electric fields applied along the growth direction. The results allow us to characterize the energy level structure of lateral quantum dot molecules and the spectral signatures of both charging and many-body interactions.We present experimental evidence for the existence of molecular-like delocalized states for electrons in the first excited energy shell.

 


Graphical Abstract



Spectroscopic signatures of many-body interactions

Spectroscopic signatures of many-body interactions

 

TITLE: In(Ga)As/GaAs(001) quantum dot molecules probed by nano-focus high resolution x-ray diffraction with 100nm resolution
AUTHORS: M.Dubslaff, M.Hanke, M.Burghammer, S.SchÄoder, R.Hoppe, C.G.Schroer, Yu.I.Mazur, Zh.M.Wang, J. H. Lee, G.J.Salamo
JOURNAL/BOOK TITLE:
Applied Physics Letters
VOLUME: 98                                  FIRST PAGE: 213105
YEAR OF PUBLICATION: 2011                                    TYPE: A                        IF: 3.554


Abstract



 

In(Ga)As quantum dots, which laterally self-assemble into quantum dot molecules, have been studied by scanning x-ray nanodiffraction, finite element calculations and subsequent kinematical diffraction simulations. X-ray beam sizes of 100 nm enable small scattering volumes comparable to the object size at extremely high local flux densities ~10^4 photons nm^−2 s^−1. By that bulkcontributions to the scattering are effectively reduced. Area maps of various individual quantum dot molecules have been measured, whereas the diffraction patterns therein reveal spatially resolved information about the inter quantum dot position correlation function. © 2011 American Institute of Physics. [doi:10.1063/1.3593960]


 



Graphical Abstract



Appl. Phys. Lett. 98, 213105  (2011)

 

TITLE: Enhanced photo-sensitivity through Increased Light Trapping by Nano-structuring using MWCNT etch mask
AUTHORS: M. Y. Hwang, H. S. Kim, E. S. Kim, J. H. Lee and S. M. Koo
JOURNAL/BOOK TITLE: Nanoscale Research Letters
VOLUME: 6                                 FIRST PAGE: 573
YEAR OF PUBLICATION:
2011                                   TYPE: A                      IF: 2.557

Abstract



 

We demonstrate an enhanced photo-sensitivity through an increased light-trapping using surface nano-structuring technique by inductively coupled plasma (ICP) etching on multi-walled carbon nanotube (MWCNT) etch masked Si with hexamethyl-disilazane (HMDS) dispersion. In order for a systematic comparison, four samples are prepared respectively by conventional photolithography and ICP etching using MWCNT as a etch mask. MWCNT etched Si with HMDS dispersion shows the highest RMS roughness and the lowest reflectance of the four. Two test device structures are fabricated with active regions of bare-Si as a reference and MWCNT etch masked Si with HMDS dispersion. The increased light trapping was most significant at mid-UV, somewhat less at visible and less noticeable at infrared. With an ICP etched Si using CNT HMDS dispersion, photo-sensitivity is very sharply increased. This result can lead to applications in optoelectronics where the enhancement in light trapping is important.

 


Graphical Abstract



Nanoscale Research Letters 2011, 6:573

Nanoscale Research Letters 2011, 6:573


 

TITLE: Low Density Quantum Dot Molecules by Selective Etching using In Droplet as a Mask
AUTHORS: J. H. Lee, Zh. M. Wang, Y. K. Hirono, V. G. Dorogan, Y. I Mazur, E. S. Kim, S. M. Koo, S. H. Park, S. M. Song and G. J. Salamo
JOURNAL/BOOK TITLE: IEEE Transactions on Nanotechnology 
VOLUME: 10                                  FIRST PAGE: 600
YEAR OF PUBLICATION: 2011                                   KEY: A                         IF: 2.154

Abstract



 

We demonstrate low-density quantum dot molecules (QDMs) by selective etching using In droplets as a mask. Selective etching is performed with InGaAs QDMs buried underneath GaAs capping layer, on which In droplets are formed by droplet epitaxy using molecular beam epitaxy. During the chemical etching, the droplets act as a mask and QDMs underneath the droplets that only survive. Photoluminescence measurement from the selectively etched QDMs in mesa structures shows a much reduced intensity, which indicates low-density QDMs. This technique provides a simple and flexible method to attain low-densityQDMs. The density can be easily modified by the control of the size and density of In droplets, which is suitable for single QDM spectroscopy and for their device applications.

 


Graphical Abstract



IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 10, NO. 3, MAY 2011IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 10, NO. 3, MAY 2011


 

TITLE: Anti-Reflective Nano- and Micro-Structures On 4H-SiC for Photodiodes
AUTHORS: M. S. Kang, S. J. Joo, W. Bahng, J. H. Lee, and S. M. Koo
JOURNAL/BOOK TITLE: Nanoscale Research Letters
VOLUME: 6                                 FIRST PAGE: 236
YEAR OF PUBLICATION: 2011                                   TYPE: A                       IF: 2.894

Abstract



 

In this study, nano-scale honeycomb-shaped structures with anti-reflection properties were successfully formed on SiC. The surface of 4H-SiC wafer after a conventional photolithography process was etched by inductively coupled plasma. We demonstrate that the reflection characteristic of the fabricated photodiodes has significantly reduced by 55% compared with the reference devices. As a result, the optical response Iillumination/Idark of the 4H-SiC photodiodes were enhanced up to 178%, which can be ascribed primarily to the improved light trapping in the proposed nano-scale texturing.

 


Graphical Abstract



Nanoscale Research Letters 2011, 6:236

Nanoscale Research Letters 2011, 6:236


 

TITLE: Evolution of self-assembled InGaAs tandem nanostructures consisting a hole and pyramid on type-A high index GaAs substrates by droplet epitaxy
AUTHORS: J. H. Lee, Zh. M. Wang, E. S. Kim, N. Y. Kim, S. H. Park and G. J. Salamo
JOURNAL/BOOK TITLE: IEEE Transactions on Nanotechnology 
VOLUME: 10                                 FIRST PAGE: 395
YEAR OF PUBLICATION: 2011                                    TYPE: A                        IF: 2.154

Abstract



 

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: (311)A (411)A, (511)A and (711)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.

 


Graphical Abstract



IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 10, NO. 3, MAY 2011

IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 10, NO. 3, MAY 2011


TITLE: Inside Back Cover: InxGa1−xAs quantum wire network-like and ordered checker board-like nanostructures on GaAs (311) by low In composition multi-layer stacking (Phys. Status Solidi A 1/2011)
AUTHORS: J. H. Lee, Zh. M. Wang, V. Yazdanpanah, E. S. Kim, S. M. Koo, S. M. Song and G. J. Salamo
JOURNAL/BOOK TITLE: Physica Status Solidi (a)
YEAR OF PUBLICATION: 2011                                   TYPE: A                      IF: 1.21
PSSA 2011 Jan
 

 

TITLE: InxGa1-xAs Quantum Wire Network-like & Ordered Checker Board-like Nanostructures on GaAs (311) by Low In composition Multi-layer Stacking
AUTHORS: J. H. Lee, Zh. M. Wang, V. Yazdanpanah, E. S. Kim, S. M. Koo, S. M. Song and G. J. Salamo
JOURNAL/BOOK TITLE: Physica Status Solidi (a)
VOLUME: 208                                 FIRST PAGE: 47
YEAR OF PUBLICATION: 2011                                    TYPE: A                      IF: 1.221

(Featured on the Journal cover of the volume 208, issue 1 of Physica Status Solidi (a))


Abstract



 

Unique quantum wire (QWR) network-like nanostructures (QWRNNs) and ordered checker board-like nanostructures (OCBNs) were demonstrated on GaAs (311) A and B by applying a low In composition multiple-layer stacking technique. More specifically, the combination of low In composition and multilayer systems, [In0.18Ga0.82As/GaAs]m wherem¼1, 4, 8, 10, 12, and 16 periods, have been investigated on GaAs (311) A and B by molecular beam epitaxy (MBE). Under a same growth condition, QWRNNs were demonstrated on GaAs (311)A whileOCBNswere fabricated on GaAs (311)B as a result of the strain accumulation and transfer through the multiple layers stacked.An appropriate control of the number of layers stacked and spacer thickness can result in an improved ordering and uniformity of QWRNNs and OCBNs.

 


Graphical Abstract



Phys. Status Solidi A 208, No. 1 (2011)


 

TITLE: InGaAs Quantum Dot Molecules during Selective Etching using In Droplet Mask
AUTHORS: J. H. Lee, Zh. M. Wang, Y. K. Hirono, E. S. Kim, S. M. Koo, V. G. Dorogan, Y. I. Mazur, S. M. Song, G. Y. Park and G. J. Salamo
JOURNAL/BOOK TITLE: Journal of physics D: Applied physics
VOLUME: 44                                   FIRST PAGE: 025102
YEAR OF PUBLICATION: 2011                                   TYPE: A                        IF: 2.083

Abstract



 

We investigated the optical transition of InGaAs quantum dot molecules (QDMs) during selective etching of GaAs using In droplets to demonstrate low-density QDMs. During the selective etching, In droplets act as nanoscale masks and only QDMs underneath the droplets survive, by which process low-density QDMs are fabricated. The thickness of selective GaAs etching is systematically varied and a gradual red-shift is observed with the increased etching thickness. The continuing red-shift can be explained by the strain relaxation due to GaAs etching. This technique to achieve low-density QDMs by selective etching using droplets as nanoscale mask is a simple and flexible approach. This study can find applications in single QDM spectroscopy and other spectroscopic techniques.

 


Graphical Abstract



J. Phys. D: Appl. Phys. 44 (2011) 025102 J. Phys. D: Appl. Phys. 44 (2011) 025102


 

TITLE: Instability of various configurations of in nano-crystals on GaAs (100) by droplet epitaxy
AUTHORS: J. H. Lee
JOURNAL/BOOK TITLE: CRYSTENGCOMM
VOLUME: 13                                 FIRST PAGE: 771
YEAR OF PUBLICATION: 2011                                    TYPE: A                       IF: 4.183 

Abstract



 

Remarkably we observe the instability of various configurations of In nano-crystals on GaAs (100). Various configurations of In nanocrystals are formed by a droplet epitaxy (DE) approach using molecular beam epitaxy (MBE). The configurations of In nanocrystals are round, squares and elongated rod shapes. When In crystals are exposed to air, a random pit begins to form. The pit formation was observed to be as deep as over 10 nm underneath the GaAs surface. Regardless of the shapes and configurations, In crystals desorb from the GaAs surface, which results in the development of strip patterns over 10 mm wide and hundreds of mm long.

 


Graphical Abstract



CrystEngComm, 2011, 13, 771?775 | 773

 

TITLE: Crystallographic plane-orientation dependent atomic force microscopy-based local oxidation of silicon carbide
AUTHORS: J. J. Ahn, Y. D. Jo, S. C. Kim, J. H. Lee, and S. M. Koo
JOURNAL/BOOK TITLE: Nanoscale Research Letters
VOLUME: 6                                 FIRST PAGE: 235
YEAR OF PUBLICATION: 2011                                    TYPE: A                       IF: 2.894

Abstract



 

The effect of crystalline plane orientations of Silicon carbide (SiC) (a-, m-, and c-planes) on the local oxidation on 4H-SiC using atomic force microscopy (AFM) was investigated. It has been found that the AFM-based local oxidation (AFM-LO) rate on SiC is closely correlated to the atomic planar density values of different crystalline planes (a-plane, 7.45 cm-2; c-plane, 12.17 cm-2; and m-plane, 6.44 cm-2). Specifically, at room temperature and under about 40% humidity with a scan speed of 0.5 μm/s, the height of oxides on a- and m-planes 4H-SiC is 6.5 and 13 nm, respectively, whereas the height of oxides on the c-plane increased up to 30 nm. In addition, the results of AFM-LO with thermally grown oxides on the different plane orientations in SiC are compared.

 



Graphical Abstract



Nanoscale Research Letters 2011, 6:235

Nanoscale Research Letters 2011, 6:235



TITLE: Journal cover of Volume 9, Issue 2 of IEEE Transactions on Nanotechnology
AUTHORS: J. H. Lee, Zh. M. Wang, Yu. Mazur, V. G. Dorogan, M. E. Ware and G. J. Salamo
JOURNAL/BOOK TITLE: IEEE Transactions on Nanotechnology 
VOLUME: 9                                 FIRST PAGE: 149
YEAR OF PUBLICATION: 2010                                 TYPE: A                      IF: 2.154
Journal cover of the volume 9, issue 2 of IEEE Transactions on Nanotechnology
 


TITLE:Evolution of Various Nanostructures and Preservation of Self-Assembled InAs Quantum Dots during GaAs Capping
AUTHORS:J. H. Lee, Zh. M. Wang, Yu. Mazur, V. G. Dorogan, M. E. Ware and G. J. Salamo
JOURNAL/BOOK TITLE: IEEE Transactions on Nanotechnology 
VOLUME: 9                                 FIRST PAGE: 149
YEAR OF PUBLICATION:
2010                                  TYPE: A                      IF: 2.154

(Featured on the Journal cover of the volume 9, issue 2 of IEEE Transactions on Nanotechnology )

Abstract



 

The fabrication of nanostructures such as quantum rods (QRDs), quantum dot pairs (QDPs), bridged QDPs, and dimpled QDs (DQDs) is achieved by an application of a shallow GaAs layer using solid source molecular beam epitaxy (MBE). More specifically, the shape transition and evolution process as well as the preservation of original dome shape of self-assembled InAs quantum dots (QDs) are studied during the thin capping of GaAs layers in terms of morphology and optical property. As QDs are required to be capped for their applications and optical characterizations, it is critical to understand the mechanism during the capping process. QDs go through a significant shape transition and eventually evolve into various nanostructures at temperatures between 500 ?C and 400 ?C, while the original dome shape can be maintained at temperatures below 360 ?C. The shape evolutions aremainly driven by diffusion process induced by redistribution of surface chemical potential and strain matrix. Photoluminescence (PL) results show a blue-shift with increasing capping temperature for a fixed capping thickness, which adequately matches with morphological evolution.

 



Graphical Abstract



IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 9, NO. 2, MARCH 2010       IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 9, NO. 2, MARCH 2010

 

TITLE: High Temperature-Stable Operation of Nano-Ribbon Field-Effect Transistors
AUTHORS: C. Y. Choi, J. H. Lee, J. H. Koh, J. G. Ha, S. M. Koo, and S. Kim
JOURNAL/BOOK TITLE:Nanoscale Research Letters
VOLUME: 5                                  FIRST PAGE: 1795
YEAR OF PUBLICATION: 2010                                   TYPE: A                      IF:2.894

Abstract



 

We experimentally demonstrated that nanoribbon field-effect transistors can be used for stable hightemperature applications. The on-current level of the nanoribbon FETs decreases at elevated temperatures due to the degradation of the electron mobility. We propose two methods of compensating for the variation of the current level with the temperature in the range of 25–150 C, involving the application of a suitable (1) positive or (2) negative substrate bias. These two methods were compared by two-dimensional numerical simulations. Although both approaches show constant on-state current saturation characteristics over the proposed temperature range, the latter shows an improvement in the off-state control of up to five orders of magnitude (-5.2 x 10^-6).

 


Graphical Abstract



Nanoscale Res Lett (2010) 5:1795?1799      Nanoscale Res Lett (2010) 5:1795?1799

 

TITLE: Strongly Confined Excitons in Self-assembled InGaAs Quantum Dot Clusters Produced by a Hybrid Growth Method
AUTHORS: Megan Creasey, Xiaoqin Li, J. H. Lee, Zh. M. Wang, and G. J. Salamo
JOURNAL/BOOK TITLE: Journal of Applied Physics
VOLUME: 107                           FIRST PAGE: 104302 
YEAR OF PUBLICATION: 2010                                   KEY: A                       IF: 2.201

Abstract



 

We investigate the optical properties of newly developed InGaAs quantum dot clusters (QDCs). The QDCs are produced using a hybrid growth method that combines droplet homoepitaxy and Stranski–Krastanov growth modes. We focus on a particular geometry, where six individual quantum dots (QDs) spontaneously form a structure morphologically similar to a benzene ring. We observe narrow exciton resonances in microphotoluminescence measurements. Temperature and excitation density dependence of the exciton resonances are investigated. Our experiments suggest that excitons are strongly confined in individual QDs instead of residing in all QDs in the cluster. © 2010 American Institute of Physics. [doi:10.1063/1.3369389]

 


Graphical Abstract



J. Appl. Phys. 107, 104302 (2010)


 

TITLE: Various Quantum- and Nano-structures by using III-V Droplet Epitaxy on GaAs Substrates
AUTHORS: J. H. Lee, Zh. M. Wang, E. S. Kim, N. Y. Kim, S. H. Park and G. J. Salamo
JOURNAL/BOOK TITLE:
Nanoscale Research Letters
VOLUME: 5                                 FIRST PAGE: 308
YEAR OF PUBLICATION: 2010                                    TYPE: A                      IF: 2.894

Abstract



 

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 ringshaped nanostructures are formed on GaAs (100). The formation mechanism of various nanostructures can be understood in terms of intermixing, surface diffusion, and surface reconstruction.

 


Graphical Abstract



Nanoscale Res Lett (2010) 5:308?314


TITLE: Back Cover (Phys. Status Solidi A 2/2010)

AUTHORS: J. H. Lee, Zh. M. Wang, E. S. Kim, N. Y. Kim, S. H. Park and G. J. Salamo

JOURNAL/BOOK TITLE: Physica Status Solidi (a)

YEAR OF PUBLICATION: 2010                                  TYPE: A                           IF: 1.21
Self-assembled InGaAs tandem nanostructures consisting a hole and pyramid on GaAs (311)A by droplet epitaxy
 

 

TITLE: Self-assembled InGaAs tandem nanostructures consisting a hole and pyramid on GaAs (311)A by droplet epitaxy
AUTHORS: J. H. Lee, Zh. M. Wang, E. S. Kim, N. Y. Kim, S. H. Park and G. J. Salamo
JOURNAL/BOOK TITLE: Physica Status Solidi (a)
VOLUME: 207                                 FIRST PAGE: 348
YEAR OF PUBLICATION: 2010                                  TYPE: A                      IF: 1.21
(Featured on the Journal cover of the volume
207, issue 2 of Physica Status Solidi (a))

Abstract



 

We report on the fabrication self-assembled tandem (pyramidalholed) InGaAs nanostructures on GaAs (311)A in comparison with the nanostructures on (100) surface. Under an identicalgrowth condition, the fabricated nanostructures are characteristically dissimilar; ring-shaped nanostructures on GaAs (100) and pyramidal-holed nanostructures on (311)A. The underlying formation mechanism of these interesting nanostructures can be understood in terms of intermixing, dissolution of GaAs substrate and surface diffusion driven by a surface reconstruction. The size and density of nanostructures can be controlled by modifying the droplet size, density, and thermal energy applied during the fabrication of droplets and nanostructures. These unique InGaAs nanostructures can offer promising applications in optoelectronics.

 


Graphical Abstract




 

TITLE: Various Configurations of In Nanostructures on GaAs (100) by Droplet Epitaxy
AUTHORS: J. H. Lee, Zh. M. Wang, Y. K. Hirono, E. S. Kim, N. Y. Kim, S. H. Park, C. Wang and G. J. Salamo
JOURNAL/BOOK TITLE: CRYSTENGCOMM
VOLUME: 12                                   FIRST PAGE: 3404
YEAR OF PUBLICATION: 2010                                    TYPE: A                      IF: 4.183 

Abstract



 

In sharp contrast to the general belief in the round shape of In droplets, we report various configurations of In nanostructures. Various configurations of self-assembled In nanostructures are demonstrated by droplet epitaxy on GaAs (100) using molecular beam epitaxy. Square, rectangle, pentagonal geometries and elongated rod-like configurations are realized on GaAs (100). The formation of facets is clearly observed on the top and side of the In nanostructures. Co-existence of both round and square shapes of In nanostructures is captured, which shows the sharp transition between the two.

 


Graphical Abstract



CrystEngComm, 2010, 12, 3404?3408


 

TITLE: On the complex behavior of strain relaxation in (In,Ga)As/GaAs (001) quantum dot molecules
AUTHORS: M. Hanke, M. Dubslaff, M. Schmidbauer, Zh. M. Wang, Yu. I. Mazur, P. M. Lytvyn, J. H. Lee, and G. J. Salamo
JOURNAL/BOOK TITLE: Applied Physics Letters
VOLUME: 95                                   FIRST PAGE: 023103
YEAR OF PUBLICATION: 2009                                   KEY: A                      IF: 3.726

Abstract



 

A detailed growth scenario of surface quantum dot molecules QDM in the system (In,Ga)As/ GaAs(001) has been investigated in terms of shape and elastic strain evolution. QDMs are grown by a combined approach using droplet epitaxy for initial homoepitaxial GaAs mounds, which subsequently serve as nucleation spots for surrounding In,GaAs surface quantum dots. Atomic force micrographs trace a detailed pathway toward the final QDM containing up to six quantum dots with perfect inherent symmetry. Synchrotron-based grazing incidence diffraction together with grazing incidence small angle x-ray scattering reveal a relaxation behavior, which for all growth stages comprises a strained lattice along 1¯10 and partial elastic relaxation along [110]. Numerical finite element calculations on the three-dimensional strain profile support the experimental findings. © 2009 American Institute of Physics. [DOI: 10.1063/1.3176409]

 


Graphical Abstract



Appl. Phys. Lett. 95, 023103 (2009)Appl. Phys. Lett. 95, 023103 (2009)


 

TITLE: Size and density control of In droplets at near room temperatures
AUTHORS: J. H. Lee, Zh. M. Wang, N. Y. Kim and G. J. Salamo
JOURNAL/BOOK TITLE: Nanotechnology 
VOLUME: 20                              FIRST PAGE: 285602
YEAR OF PUBLICATION: 2009                                   TYPE: A                      IF: 3.446

Abstract



 

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 (Tsub) and monolayer (ML) coverage. For a range of density (∼109–1010 cm−2), 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 Tsub. For a fixed Tsub, 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.

 

Graphical Abstract



Nanotechnology 20 (2009) 285602


 

TITLE: Tuning the emission profiles of various self-assembled InxGa1−xAs nanostructures by rapid thermal annealing
AUTHORS: J. H. Lee, Zh. M. Wang, Yu. Mazur, V. G. Dorogan, M. E. Ware and G. J. Salamo
JOURNAL/BOOK TITLE: Journal of Applied Physics
VOLUME: 106                                 FIRST PAGE: 073106 
YEAR OF PUBLICATION: 2009                                   TYPE: A                      IF: 2.201

Abstract



 

Tuning the emission profiles of various novel InxGa1−xAs nanostructures, such as quantum rods, quantum dot pairs (QDPs), bridged QDPs, dimpled quantum dots (QDs), and low-temperature-capped QDs, is demonstrated by postgrowth rapid thermal annealing. Specifically, improved optical properties, such as a much narrower full width at half maximum of 16 meV and a continuous blueshift, are demonstrated. The enhanced optical properties are attributed to the interchange of In and Ga atoms induced by both defect-assisted intermixing and strain-assisted intermixing. These results can find applications as an optical enhancement in nanostructures is critical for the improvements on device functionality. © 2009 American Institute of Physics.
[doi:10.1063/1.3213095]

 


Graphical Abstract



J. Appl. Phys. 106, 073106 (2009)


 

TITLE: The Control on Size and Density of InAs QDs by Droplet Epitaxy
AUTHORS: J. H. Lee, Zh. M. Wang and G. J. Salamo
JOURNAL/BOOK TITLE: IEEE Transactions on Nanotechnology  
VOLUME: 8                                     FIRST PAGE: 431 
YEAR OF PUBLICATION: 2009                                   TYPE: A                      IF: 2.154


Abstract



 

We report on the ability to grow InAs quantum dots (QDs) by droplet epitaxy (DE) using solid-source molecular beam epitaxy (MBE). In particular, the control of the size and density of InAs QDs at near room temperatures are achieved as a function of substrate temperature and crystallization condition. For a typical range of QD density (∼10^9 to 10^10 cm−2 ), the growth window is revealed to be fairly narrow (∼20 ?C). In droplets are extremely sensitive to surface diffusion and arsenic background pressure even at near room temperatures. As a result, a very careful fabrication procedure is required to crystallize In droplets in order to fabricate desired shape of InAs QDs. For this purpose, we developed a double-step crystallization process, in whichAs background recovery and high-temperature crystallization are introduced. In addition, the results by DE are compared with QDs fabricated by Stranski–Krastanow (S-K) growth approach in terms of size and density. The results can find applications in optoelectronics as the fabrication of QDs by DE approach has more flexibility over S-K approach, i.e., more freedom of size and density control.

 


Graphical Abstract



IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 8, NO. 4, JULY 2009      IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 8, NO. 4, JULY 2009


 

TITLE: InAs Quantum Dot Clusters Grown on GaAs Droplet Templates: Surface Morphologies and Optical Properties
AUTHORS: B. L. Liang, V. G. Dorogan, Yu. I. Mazur, N. W. Strom, J. H. Lee, K. A. Sablon, Zh. M. Wang, G. J. Salamo
JOURNAL/BOOK TITLE: Journal of Nanoscience and Nanotechnology
VOLUME: 9                                 FIRST PAGE: 3320
YEAR OF PUBLICATION: 2009                                   KEY: A                      IF: 1.929

Abstract



 

GaAs nano-mounds formed by droplet epitaxy are used as templates for growth of self-assembled InAs quantum dot clusters (QDCs).These QDCs are found to contain an average of thirteen dots per cluster, of which there are two families of different sized quantum dots.Excitation intensitydependent photoluminescence (PL) demonstrates that there is no lateral coupling between the two different size quantum dots.Later al transfer of carriers is observed between different size quantum dots due to thermal activation as seen in their different temperature-dependent optical behaviors.

 


Graphical Abstract



Journal of Nanoscience and Nanotechnology Vol.9, 3320?3324, 2009

 

TITLE: Design of Nanostructure Complexes by droplet epitaxy
AUTHORS: J. H. Lee, Zh. M. Wang, Yu. Mazur, V. G. Dorogan, M. E. Ware and G. J. Salamo
JOURNAL/BOOK TITLE: Crystal growth & design
VOLUME: 9                                  FIRST PAGE: 715
YEAR OF PUBLICATION: 2009                                   TYPE: A                      IF: 4.215

Abstract



 

We demonstrate a number of unseen self-assembled nanostructure complexes fabricated on various GaAs surface indexes by droplet epitaxy. Even under identical growth conditions, the configuration of nanostructure complexes is distinctive on each surface. The morphology evolution of nanostructure complexes is kinetically and energetically analyzed in determining the correlation between shape of nanostructure complexes and atomic surface matrixes with atomic ball-stick models. By systematically varying growth environment, we report many uncanny nanostructure complexes on given surface indexes.

 


Graphical Abstract



Crystal Growth & Design, Vol. 9, No. 2, 2009

 
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