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- ItemHigh-Resolution Inkjet Printing of Quantum Dot Light-Emitting Microdiode Arrays(Weinheim : Wiley-VCH Verlag, 2020) Yang, P.; Zhang, L.; Kang, D.J.; Strahl, R.; Kraus, T.The direct printing of microscale quantum dot light-emitting diodes (QLEDs) is a cost-effective alternative to the placement of pre-formed LEDs. The quality of printed QLEDs currently is limited by nonuniformities in droplet formation, wetting, and drying during inkjet printing. Here, optimal ink formulation which can suppress nonuniformities at the pixel and array levels is demonstrated. A solvent mixture is used to tune the ejected droplet size, ensure wetting, and provoke Marangoni flows that prevent coffee stain rings. Arrays of green QLED devices are printed at a resolution of 500 pixels in.−1 with a maximum luminance of ≈3000 cd m−2 and a peak current efficiency of 2.8 cd A−1. The resulting array quality is sufficient to print displays at state-of-the-art resolutions.
- ItemLasing by Template-Assisted Self-Assembled Quantum Dots(Weinheim : Wiley-VCH, 2023) Aftenieva, Olha; Sudzius, Markas; Prudnikau, Anatol; Adnan, Mohammad; Sarkar, Swagato; Lesnyak, Vladimir; Leo, Karl; Fery, Andreas; König, Tobias A.F.Miniaturized laser sources with low threshold power are required for integrated photonic devices. Photostable core/shell nanocrystals are well suited as gain material and their laser properties can be exploited by direct patterning as distributed feedback (DFB) lasers. Here, the 2nd-order DFB resonators tuned to the photoluminescence wavelength of the QDs are used. Soft lithography based on template-assisted colloidal self-assembly enables pattern resolution in the subwavelength range. Combined with the directional Langmuir–Blodgett arrangement, control of the waveguide layer thickness is further achieved. It is shown that a lasing threshold of 5.5 mJ cm−2 is reached by a direct printing method, which can be further reduced by a factor of ten (0.6 mJ cm−2) at an optimal waveguide thickness. Moreover, it is discussed how one can adjust the DFB geometries to any working wavelength. This colloidal approach offers prospects for applications in bioimaging, biomedical sensing, anti-counterfeiting, or displays.
- ItemPhotoluminescence investigation of strictly ordered Ge dots grown on pit-patterned Si substrates(Bristol : IOP Publ., 2015) Brehm, Moritz; Grydlik, Martyna; Tayagaki, Takeshi; Langer, Gregor; Schäffler, Friedrich; Schmidt, Oliver G.We investigate the optical properties of ordered Ge quantum dots (QDs) by means of micro-photoluminescence spectroscopy (PL). These were grown on pit-patterned Si(001) substrates with a wide range of pit-periods and thus inter QD-distances (425–3400 nm). By exploiting almost arbitrary inter-QD distances achievable in this way we are able to choose the number of QDs that contribute to the PL emission in a range between 70 and less than three QDs. This well-defined system allows us to clarify, by PL-investigation, several points which are important for the understanding of the formation and optical properties of ordered QDs. We directly trace and quantify the amount of Ge transferred from the surrounding wetting layer (WL) to the QDs in the pits. Moreover, by exploiting different pit-shapes, we reveal the role of strain-induced activation energy barriers that have to be overcome for charge carriers generated outside the dots. These need to diffuse between the energy minimum of the WL in and between the pits, and the one in the QDs. In addition, we demonstrate that the WL in the pits is already severely intermixed with Si before upright QDs nucleate, which further enhances intermixing of ordered QDs as compared to QDs grown on planar substrates. Furthermore, we quantitatively determine the amount of Ge transferred by surface diffusion through the border region between planar and patterned substrate. This is important for the growth of ordered islands on patterned fields of finite size. We highlight that the Ge WL-facets in the pits act as PL emission centres, similar to upright QDs.
- ItemCorrelative Fluorescence- and Electron Microscopy of Whole Breast Cancer Cells Reveals Different Distribution of ErbB2 Dependent on Underlying Actin(Lausanne : Frontiers Media, 2020) Dahmke, I.N.; Trampert, P.; Weinberg, F.; Mostajeran, Z.; Lautenschläger, F.; de Jonge, N.Epidermal growth factor receptor 2 (ErbB2) is found overexpressed in several cancers, such as gastric, and breast cancer, and is, therefore, an important therapeutic target. ErbB2 plays a central role in cancer cell invasiveness, and is associated with cytoskeletal reorganization. In order to study the spatial correlation of single ErbB2 proteins and actin filaments, we applied correlative fluorescence microscopy (FM), and scanning transmission electron microscopy (STEM) to image specifically labeled SKBR3 breast cancer cells. The breast cancer cells were grown on microchips, transformed to express an actin-green fluorescent protein (GFP) fusion protein, and labeled with quantum dot (QD) nanoparticles attached to specific anti-ErbB2 Affibodies. FM was performed to identify cellular regions with spatially correlated actin and ErbB2 expression. For STEM of the intact plasma membrane of whole cells, the cells were fixed and covered with graphene. Spatial distribution patterns of ErbB2 in the actin rich ruffled membrane regions were examined, and compared to adjacent actin-low regions of the same cell, revealing an association of putative signaling active ErbB2 homodimers with actin-rich regions. ErbB2 homodimers were found absent from actin-low membrane regions, as well as after treatment of cells with Cytochalasin D, which breaks up larger actin filaments. In both latter data sets, a significant inter-label distance of 36 nm was identified, possibly indicating an indirect attachment to helical actin filaments via the formation of heterodimers of ErbB2 with epidermal growth factor receptor (EGFR). The possible attachment to actin filaments was further explored by identifying linear QD-chains in actin-rich regions, which also showed an inter-label distance of 36 nm.
- ItemInterdot Lead Halide Excess Management in PbS Quantum Dot Solar Cells(Weinheim : Wiley-VCH, 2022) Albaladejo‐Siguan, Miguel; Becker‐Koch, David; Baird, Elizabeth C.; Hofstetter, Yvonne J.; Carwithen, Ben P.; Kirch, Anton; Reineke, Sebastian; Bakulin, Artem A.; Paulus, Fabian; Vaynzof, YanaLight-harvesting devices made from lead sulfide quantum dot (QD) absorbers are one of the many promising technologies of third-generation photovoltaics. Their simple, solution-based fabrication, together with a highly tunable and broad light absorption makes their application in newly developed solar cells, particularly promising. In order to yield devices with reduced voltage and current losses, PbS QDs need to have strategically passivated surfaces, most commonly achieved through lead iodide and bromide passivation. The interdot spacing is then predominantly filled with residual amorphous lead halide species that remain from the ligand exchange, thus hindering efficient charge transport and reducing device stability. Herein, it is demonstrated that a post-treatment by iodide-based 2-phenylethlyammonium salts and intermediate 2D perovskite formation can be used to manage the lead halide excess in the PbS QD active layer. This treatment results in improved device performance and increased shelf-life stability, demonstrating the importance of interdot spacing management in PbS QD photovoltaics.
- ItemBis(stearoyl) Sulfide: A Stable, Odor-Free Sulfur Precursor for High-Efficiency Metal Sulfide Quantum Dot Photovoltaics(Weinheim : Wiley-VCH, 2023) Albaladejo‐Siguan, Miguel; Prudnikau, Anatol; Senina, Alina; Baird, Elizabeth C.; Hofstetter, Yvonne J.; Brunner, Julius; Shi, Juanzi; Vaynzof, Yana; Paulus, FabianThe synthesis of metal sulfide nanocrystals is a crucial step in the fabrication of quantum dot (QD) photovoltaics. Control over the QD size during synthesis allows for precise tuning of their optical and electronic properties, making them an appealing choice for electronic applications. This flexibility has led to the implementation of QDs in both highly-efficient single junction solar cells and other optoelectronic devices including photodetectors and transistors. Most commonly, metal sulfide QDs are synthesized using the hot-injection method utilizing a toxic, and air- and moisture-sensitive sulfur source: bis(trimethylsilyl) sulfide ((TMS)2S). Here, bis(stearoyl) sulfide (St2S) is presented as a new type of air-stable sulfur precursor for the synthesis of sulfide-based QDs, which yields uniform, pure, and stable nanocrystals. Photovoltaic devices based on these QDs are equally efficient as those fabricated by (TMS)2S but exhibit enhanced operational stability. These results highlight that St2S can be widely adopted for the synthesis of metal sulfide QDs for a range of optoelectronic applications.
- ItemBroadening of mode-locking pulses in quantum-dot semiconductor lasers : simulation, analysis and experiments(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2010) Radziunas, Mindaugas; Vladimirov, Andrei G.; Viktorov, Evgeny A.; Fiol, Gerrit; Schmeckebier, Holger; Bimberg, DieterWe consider a mode-locked quantum-dot edge-emitting semiconductor laser consisting of a reverse biased saturable absorber and a forward biased amplifying section. To describe the dynamics of this laser we use the traveling wave model taking into account carrier exchange processes between a reservoir and the quantum dots. A comprehensive parameter study is presented and an analysis of mode-locking pulse broadening with an increase of injection current is performed. The results of our theoretical analysis are supported by experimental data demonstrating a strong pulse asymmetry in a monolithic two section quantum dot mode-locked laser
- ItemHybrid quantum-classical modeling of quantum dot devices(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2017) Kantner, Markus; Mittnenzweig, Markus; Koprucki, ThomasThe design of electrically driven quantum dot devices for quantum optical applications asks for modeling approaches combining classical device physics with quantum mechanics. We connect the well-established fields of semi-classical semiconductor transport theory and the theory of open quantum systems to meet this requirement. By coupling the van Roosbroeck system with a quantum master equation in Lindblad form, we obtain a new hybrid quantum-classical modeling approach, which enables a comprehensive description of quantum dot devices on multiple scales: It allows the calculation of quantum optical figures of merit and the spatially resolved simulation of the current flow in realistic semiconductor device geometries in a unified way. We construct the interface between both theories in such a way, that the resulting hybrid system obeys the fundamental axioms of (non-)equilibrium thermodynamics. We show that our approach guarantees the conservation of charge, consistency with the thermodynamic equilibrium and the second law of thermodynamics. The feasibility of the approach is demonstrated by numerical simulations of an electrically driven single-photon source based on a single quantum dot in the stationary and transient operation regime.
- ItemSurface effects of vapour-liquid-solid driven Bi surface droplets formed during molecular-beam-epitaxy of GaAsBi([London] : Macmillan Publishers Limited, part of Springer Nature, 2016) Steele, J.A.; Lewis, R.A.; Horvat, J.; Nancarrow, M.J.B.; Henini, M.; Fan, D.; Mazur, Y.I.; Schmidbauer, M.; Ware, M.E.; Yu, S.-Q.; Salamo, G.J.Herein we investigate a (001)-oriented GaAs1−xBix/GaAs structure possessing Bi surface droplets capable of catalysing the formation of nanostructures during Bi-rich growth, through the vapour-liquid-solid mechanism. Specifically, self-aligned “nanotracks” are found to exist trailing the Bi droplets on the sample surface. Through cross-sectional high-resolution transmission electron microscopy the nanotracks are revealed to in fact be elevated above surface by the formation of a subsurface planar nanowire, a structure initiated mid-way through the molecular-beam-epitaxy growth and embedded into the epilayer, via epitaxial overgrowth. Electron microscopy studies also yield the morphological, structural and chemical properties of the nanostructures. Through a combination of Bi determination methods the compositional profile of the film is shown to be graded and inhomogeneous. Furthermore, the coherent and pure zincblende phase property of the film is detailed. Optical characterisation of features on the sample surface is carried out using polarised micro-Raman and micro-photoluminescence spectroscopies. The important light producing properties of the surface nanostructures are investigated through pump intensity-dependent micro-PL measurements, whereby relatively large local inhomogeneities are revealed to exist on the epitaxial surface for important optical parameters. We conclude that such surface effects must be considered when designing and fabricating optical devices based on GaAsBi alloys.
- ItemDynamics of Broadband Lasing Cascade from a Single Dot-in-well InGaAs Microdisk([London] : Macmillan Publishers Limited, part of Springer Nature, 2019) Talalaev, Vadim; Kryzhanovskaya, Natalia; Tomm, Jens W.; Rutckaia, Viktoriia; Schilling, Joerg; Zhukov, AlexeyThe development of a fast semiconductor laser is required for the realization of next-generation telecommunication applications. Since lasers operating on quantum dot ground state transitions exhibit only limited gain due to the saturation effect, we investigate lasing from excited states and compare its corresponding static and dynamic behavior to the one from the ground state. InAs quantum dots (QDs) grown in dot-in-well (DWELL) structures allowed to obtain light emission from ground and three excited states in a spectral range of 1.0–1.3 μm. This emission was coupled to whispering gallery modes (WGMs) of a 6 μm microdisk resonator and studied at room temperature by steady-state and time-resolved micro-photoluminescence. We demonstrate a cascade development of lasing arising from the ladder of quantum dot states, and compare the lasing behavior of ground and excited state emission. While the lasing threshold is being increased from the ground state to the highest excited state, the dynamic behavior is improved: turn-on times and lifetimes of WGMs become shorter paving the way towards high frequency direct driven microlasers. © 2019, The Author(s).