Viktoriia E. Babicheva, Georgia State University
Sasan Fathpour, University of Central Florida
Juejun Hu, Massachusetts Institute of Technology
Volker J. Sorger, The George Washington University, School of Engineering and Applied Science
GG3: Light Emitting Devices I
Volker J. Sorger
Viktoriia E. Babicheva
Monday PM, November 30, 2015
Hynes, Level 1, Room 103
2:30 AM - *GG3.01
Microscale Light Emitting Diodes and Lasers for Multifunctional Display Systems and On-Chip Optoelectronics
John A. Rogers 1
1Univ of Illinois Urbana United StatesShow Abstract
This talk summarizes advances in the development of microscale, high-performance light emitting diodes and lasers together with methods for their rapid, deterministic assembly on foreign substrates, ranging from silicon wafers to glass plates and plastic sheets. Applications in hybrid integration of III-V devices on Si platforms for next generation photonic integrated circuits will be highlighted.
3:00 AM - GG3.02
Nanoporous Metal Thin Films: Multifunctional Platforms for Influencing the Performance of Organic Light-Emitting Devices
Zeqing Shen 1 Deirdre O'Carroll 2 1 3
1Rutgers University Piscataway United States2Rutgers University Piscataway United States3Rutgers University Piscataway United StatesShow Abstract
To expand their applications in commercial products, methods to increase organic optoelectronic device efficiency are attracting a lot of attention. Many studies focusing on tuning the molecular morphology, photophysics and electrical properties of organic materials to improve internal quantum efficiency of the devices or improving the light extraction/trapping ability of the device structure have been conducted to improve device efficiencies . In our study, we investigate nanoporous metallic thin films as multifunctional platforms for influencing molecular organization, photophysics and light-management in organic conjugated polymer semiconductor thin films for optoelectronic applications.
Nanoporous Ag (NPAg) thin films (>1.5 cm2) with different pore sizes and porosities are fabricated using the thermally-assisted dewetting method . Grazing-incidence wide-angle X-ray scattering data show that conjugated polymer chain organization can be affected by NPAg in different ways. For example, NPAg can increase the fraction of edge-on oriented poly(3-hexylthiophene) (P3HT) chains and decrease the intermolecular π-π stacking distance relative to P3HT on planar Ag. For smaller pore widths and larger porosity, the changes are more pronounced. However, for polyfluorene-based polymers (poly(9,9-dioctylfluorene), PFO and poly(9,9-dioctylfluorene-alt-benzothiadiazole, F8BT) only NPAg with larger pore size is found to alter chain orientation. These observed changes in molecular organization with pore size and porosity could allow the electrical properties of organic active layers in thin-film optoelectronic devices to be tuned .
Moreover, significant photoluminescence (PL) enhancements were achieved for PFO (up to 22), F8BT (up to 18) and P3HT (up to 26) on NPAg films relative to that on glass. Four mechanisms are propose to contribute to the large PL enhancement: 1) redistribution of emission by Ag; 2) redirection of emission by nanopores; 3) local electromagnetic field effects; and 4) polymer chain morphology changes caused by NPAg. Both redistribution and redirection of emission by Ag and the nanopores are believed to be the most important emission enhancement factors in polymers with high intrinsic quantum efficiencies (IQE) (i.e., PFO and F8BT). While redistribution of emission by Ag and local electromagnetic field effects were believed to be the most important factors in polymers with low IQE (i.e., P3HT) . Angle-resolved PL measurements are under way to study the redirection ability of nanopores together with single-pore spectroscopy and time-resolved absorption and emission measurements to investigate local electromagnetic field effects of NPAg.
 C. E. Petoukhoff, Z. Shen, M. Jain, A. Chang, D. M. O&’Carroll, J. Photon. Energy. 2015, 5, 057002
 Z. Shen, D. M. O&’Carroll, Adv. Funct. Mater. 2015, 25, 3302
 M. Aryal, K. Trivedi, W. Hu. ACS Nano. 2009, 3, 3085
3:15 AM - GG3.03
Dynamic Control of Erbium Spontaneous Emission at Sub-Lifetime Speeds Using VO2 Phase-Change
Sebastien Cueff 1 3 Dongfang Li 1 You Zhou 2 Franklin Wong 2 Jonathan A Kurvits 1 Shriram Ramanathan 2 Rashid Zia 1
1Brown University Providence United States2Harvard University Cambridge United States3Institut des Nanotechnologies de Lyon Lyon FranceShow Abstract
The high quantum yield of phosporescent emitters makes them widely used in devices such as amplifiers, displays, lasers, and LEDs. However, these quantum emitters are usually considered impractical for high speed applications because of their intrinsically long lifetimes.
We will present a new framework to transform “slow” phosphorescent emitters into high-speed integrated nanoscale light sources, without affecting their high quantum efficiency. Rather than modulating the excited state electronic population of the emitter, we dynamically control the local optical environment and directly modulate the emission rate into different modes. For that purpose, we leverage the ultrafast insulator-to-metal transition (IMT) of vanadium dioxide as well as the multipolar nature of erbium ions to demonstrate a nanoscale device with direct all-optical modulation of spontaneous emission 3 orders of magnitude faster than the lifetime limit (and with the potential for many more orders of magnitude improvement).
This principle provides a simple way to circumvent the intrinsic lifetime limit of Erbium ions and modulate their emission at high speeds. Such devices would have direct applications at the interface of communication, display, and lighting technologies as well as in biological and chemical sensing.
3:30 AM - GG3.04
Flexible and Multi-Colored Organic/Inorganic Hybrid Perovskite Light-Emitting Diodes
Tae-Woo Lee 1 Young-Hoon Kim 1 Himchan Cho 1 Jin Hyuck Heo 2 Tae-Sik Kim 1 NoSoung Myoung 3 Chang-Lyoul Lee 3 Jin-Woo Byun 1 Sang Hyuk Im 2
1POSTECH Gyungbuk Korea (the Republic of)2Kyung Hee University Suwon Korea (the Republic of)3Gwangju Institute of Science amp; Technology Gwangju Korea (the Republic of)Show Abstract
Organic/inorganic hybrid perovskites (OIPs) have been intensively studied as a promising next-generation emitters alternating conventional organic and inorganic quantum dot (QD) emitters due to high color-purity light (full width at half maximum (FWHM) ~ 20 nm) arising from exciton confinement between organic and inorganic 2-dimensional alternating layers, and their comparable ionization potential (IP) and electron affinity levels with those of typical organic materials. Despite the OIP&’s high color-purity and comparable electronic energy levels with organic semiconductors, bright electroluminescence (EL) of OIPs has been limited due to their severe intrinsic problems such as significant thermal ionization and delocalization at room temperature.
To achieve the bright EL and high efficiency in organic/inorganic hybrid perovskite light-emitting diodes (PrLEDs), large hole injection barrier from low work-function (WF) of PEDOT:PSS (~5.2 eV) to deep ionization potential (IP) of OIPs (~5.9 eV) and severe exciton quenching at the interface between PEDOT:PSS and OIP layer should be overcome. To solve those problems, we used multifunctional self-organized buffer hole injection layer (Buf-HIL) composed of PEDOT:PSS and perfluorinated polymeric acid (PFI). The WF of the self-organized gradient Buf-HIL increased gradually from the bottom surface (ca. 5.2 eV) to the top surface (ca. 5.95 eV) due to self-organization of the PFI. This gradually increasing WF can facilitate hole injection into the OIPs by reducing the hole-injection energy barrier more efficiently than can PEDOT:PSS. Furthermore, the self-organized PFI which is enriched on the top surface of the Buf-HIL can prevent exciton quenching that occurs at the interface between HIL and EML. Finally, we successfully demonstrated organic/inorganic hybrid PrLEDs with a sharp green emission (FWHM ~ 20 nm), high luminance (417 cd/m2), current efficiency (0.577 cd/A) and external quantum efficiency (0.125 %) by using CH3NH3PbBr3 as an emitting layer and Buf-HIL. Furthermore, we fabricated flexible PrLEDs on the plastic substrate for the first time. We also demonstrated multicolored PrLEDs (400 nm < lambda; < 780 nm) by substituting halogen ions (CH3NH3PbClxBryI3-x-y) and organic ammonium cation (CnH2n+1NH3PbBr3).
GG4: Quantum Dots
Volker J. Sorger
Viktoriia E. Babicheva
Monday PM, November 30, 2015
Hynes, Level 1, Room 103
4:15 AM - GG4.01
Polariton Emission from Colloidal Quantum Dots Strongly Coupled to Plasmonic Films
Sriharsha Venkata Jayanti 1 2 Kevin McPeak 1 David K. Kim 1 Paul R. Erickson 3 Sven Burger 4 5 Jian Cui 1 Ferry Prins 1 Stephan Kress 1 Aurelio Rossinelli 1 Kristopher McNeill 3 David J. Norris 1
1ETH Zurich Zurich Switzerland2University of Minnesota Minneapolis United States3ETH Zurich Zurich Switzerland4Zuse Institute Berlin Berlin Germany5JCMwave GmbH Berlin GermanyShow Abstract
Colloidal quantum dots are color-tunable, robust and bright dipole emitters that can couple to surface plasmons, electromagnetic waves bound to a metal&’s surface. When strongly coupled, light and matter states hybridize to form polariton states, which can lead to important technological advances in quantum information processing and thresholdless lasers. Despite their promise, most studies have only observed weak coupling between colloidal quantum dots and surface plasmons. Here, we demonstrate strong coupling between CdSe/CdS/ZnS core-shell quantum dots and high quality plasmonic structures, manifesting as an avoided crossing in the surface plasmon dispersion plot. With the guidance of electromagnetic simulations, large-scale silver hole arrays and quantum dots are precisely tuned to overlap both energetically and spatially to maximize light-matter interactions. When optically excited, we observe polariton emission from these states at room temperature, and obtain a Rabi splitting of 80 meV. Furthermore, by measuring power-dependent emission spectra, an equally high vacuum Rabi splitting value is extrapolated. Spectrally-resolved lifetimes reveal that the lower polariton state and uncoupled quantum dots exhibit equivalent decay times, consistent with surface plasmons strongly coupled to emitters. These results show that colloidal quantum dots are a viable and versatile optically active material for the study of strong light-matter coupling and its applications.
4:30 AM - GG4.02
Design of Efficient Light-Absorption Layers with Earth-Abundant Materials: A Tight-Binding Study on Inter-Band Transition Rate of Si:P Quantum Dots
KyuNam Cho 2 Chang-Sung Jeong 2 Hoon Ryu 1
1Korea Institute of Science and Technology Information Daejeon Korea (the Republic of)2Korea University Seoul Korea (the Republic of)Show Abstract
Photovoltaic (PV) devices have been extensively studied for applications in solar cells. However, the grid-parity of solar powers is not yet achieved due to the expensive cost of electricity compared to the cost with fossil fuels . Designs of highly efficient light absorption layers with earth-abundant materials, is thus critical as they can reduce the cost of PV cells by increasing the power-per-unit-area of solar panels. In consequence, optical properties of various materials and structures have been the central topic for research in nanoelectronics. III-V semiconductors have been known as excellent materials for light absorption layers. In particular, InAs/GaAs quantum dots (QDs) have been great interest to researchers as they exhibit high efficiency in light absorption, and have tunable optical gaps . But the expensive material cost becomes the limiting factor for the grid-parity. Earth-abundant materials such as Iron disulphide and Tin monosulphide have been studied due to their appropriate optical gaps , but the strong surface-recombination limits the device performance.
The combination of scanning tunneling microscope lithography and molecular beam epitaxy enabled a precise control of dopant placements in silicon (Si), a representative earth-abundant material. Various phosphorus (P) monolayer devices embedded in Si (Si:P) thus have been realized with the atomically precise incorporation of dopants, including planar electrodes, ultra-thin interconnects and donor-based QDs for advanced logic applications [5-7]. In this work, we expand the application scope of Si:P devices to optoelectronics with a focus on Si:P QDs. Electronic structures are calculated with the sp3d5s* tight-binding model that has shown its validity in describing Si:P devices [5-7]. We report promising properties of Si:P QDs as light absorption layers, particularly against self-assembled InAs/GaAs QDs: (I) The optical gap of single-dopant QDs is good for absorbing the natural light at ~1100um wavelengths, and is widely tunable by changing the number of P atoms in the dopant cluster. (II) The inter-band optical transition rate is much more insensitive to directions of polarization, which represents the strong potential of Si:P QDs in efficient absorption of the natural light injected from arbitrary directions. Establishing a theoretical framework of optical properties of Si:P QDs that have been rarely explored for realistically sized devices with a full atomistic model, this work presents a detailed analysis useful for potential designs of light absorption layers with Si:P QDs.
 M. Bazillan et al., Renewable Energy 53, 329 (2013)
 D. Forbes et al., Proceedings of SPIE (2014)
 P. Lazic et al., Journal of Physics: Condensed Matters 25, 465801 (2013)
 P. Sinsermsuksakul et al., Applied Physics Letters 102, 053901 (2013)
 H. Ryu et al., Nanoscale 8, 053901 (2013)
 H. Ryu et al., Small 11, 374 (2014)
 H. Ryu et al., Nano Letters 15, 450 (2015)
4:45 AM - GG4.03
Solution-Processed Vertical-Cavity Surface-Emitting All-Colloidal Quantum Dot Lasers
Burak Guzelturk 1 Yusuf Kelestemur 1 Kivanc Gungor 1 Aydan Yeltik 1 Mehmet Zafer Akgul 1 Wang Yue 2 Rui Chen 2 Cuong Dang 2 Handong Sun 2 Hilmi Volkan Demir 1 2
1Bilkent University Ankara Turkey2Nanyang Technological University Singapore SingaporeShow Abstract
Colloidal quantum dots (QDs) are highly attractive materials for full-color and solution-processed lasers. However, optical gain in these QDs has been severely limited due to nonradiative Auger recombination. To date, large-sized heterostructured nanocrystals including giant-QDs  and dot-in-rod type nanocrystals  have been shown to suppress Auger recombination. However, strongly reduced electron-hole overlap in such nanocrystals results in decreased oscillator strength and lower optical gain coefficients.
In this work, we proposed and developed core/shell CdSe/CdS QDs that simultaneously combine large oscillator strengths and increased optical gain coefficients and demonstrated high performance lasing using these tailor-made QDs incorporated into a colloidal optical cavity to achieve the first fully solution-processed vertical-cavity surface-emitting all-colloidal lasers (VCSEL) . To this end, we synthesized core/shell QDs having relatively a small size (with a total diameter of 8 nm) exhibiting polytypic crystal structure. The shell growth was performed at 310°C, which facilitated the formation of an alloyed soft-interface between the core and the shell as verified by careful XPS analysis . Through excitation intensity-dependent time-resolved fluorescence spectroscopy, we found that these alloyed core/shell QDs exhibit significantly suppressed Auger lifetime of 1.48 ns, which is similar to that of the giant-QDs and nanorods .
As a major advancement, here we achieved ultralow threshold and extremely stable optical gain using these engineered QDs. Single-photon absorption pumped amplified spontaneous emission (ASE) was achieved with an ultralow threshold of 29 µJ/cm2, and two-photon absorption pumped ASE threshold was measured to be 5 mJ/cm2, both of which set the records in their class for the colloidal QDs . This exceptionally efficient optical gain enabled us to realize the first all-colloidal lasers. For this, we developed an optical cavity using distributed Bragg reflectors (DBRs) obtained via alternative spin coating of the colloidal SiO2 and TiO2 nanoparticles. This all-colloidal laser showed remarkable two-photon absorption pumped lasing threshold as low as 730 µJ/cm2 . To the best of our knowledge, this is the best among all solution-processed semiconductors including organic molecules, conjugated polymers, nanorods, etc., reported to date .
These VCSELs demonstrated using tailor-made core/shell QDs coupled in a colloidal cavity in this work represent the first acc