Epitaxní materiály a nanostruktury

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    2.7 mu m quantum cascade detector: Above band gap energy intersubband detection
    (AIP Publishing, 2022-02-14) Giparakis, Miriam; Knotig, Hedwig; Detz, Hermann; Beiser, Maximilian; Schrenk, Werner; Schwarz, Benedikt; Strasser, Gottfried; Andrews, Aaron Maxwell
    Quantum cascade detectors (QCDs) are mid-infrared and far-infrared, low-noise, photovoltaic detectors utilizing intersubband transitions. This Letter presents an InAs/AlAs0.16Sb0.84 based QCD lattice matched to an InAs substrate. This material system exhibits properties like a low effective electron mass of the well material of 0.023 m(0), beneficial for higher optical absorption strength, and a high conduction band offset of 2.1 eV, allowing the design of QCDs in the mid-infrared and near-infrared region. The presented QCD has a peak spectral response at 2.7 mu m (0.459 eV), the center of a CO2 absorption band. To enable top side illumination, a grating was implemented. This additionally bypasses absorption by the narrow bandgap 0.345 eV (3.54 mu m) InAs substrate material. The QCD has a peak responsivity at a room temperature of 5.63 mA/W and a peak specific detectivity of 1.14 x 10(8) Jones. (c) 2022 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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    Structure and mid-infrared optical properties of spin-coated polyethylene films developed for integrated photonics applications
    (Optica Publishing Group, 2022-06-01) David, Mauro; Disnan, Davide; Lardschneider, Anna; Wacht, Dominik; Hoang, Hanh T.; Ramer, Georg; Detz, Hermann; Lendl, Bernhard; Schmid, Ulrich; Strasser, Gottfried; Hinkov, Borislav
    Polyethylene is a promising polymer for mid-infrared integrated optics due to its broad transparency and optimal refractive index. However, simple fabrication protocols that preserve its optical characteristics are needed to foster a wide range of applications and unlock its full potential. This work presents investigations of the optical and structural properties of spin-coated linear low-density polyethylene films fabricated under humidity-controlled conditions. The film thickness on polymer concentration dependence shows a non-linear behavior, in agreement with previously reported theoretical models and allowing predictive concentration-dependent thickness deposition with high repeatability. The surface roughness is on the nanometer-scale for all investigated concentrations between 1% and 10%. The crystallinity of the films was studied with the Raman spectroscopy technique. Mid-infrared ellipsometry measurements show a broad transparency range as expected for bulk material. Layer exposure to solvents revealed good stability of the films, indicating that the fabricated layers can outlast further fabrication steps. These investigations confirm the excellent properties of spin-coated thin films fabricated with our novel method, creating new opportunities for the use in photonic integrated circuits Published by Optica Publishing Group under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
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    Deep learning control of THz QCLs
    (Optica Publishing Group, 2021-07-19) Limbacher, Benedikt; Schönhuber, Sebastian; Kainz, Martin A.; Bachelard, Nicolas; Andrews, Aaron Maxwell; Detz, Hermann; Strasser, Gottfried; Darmo, Juraj; Unterrainer, Karl
    Artificial neural networks are capable of fitting highly non-linear and complex systems. Such complicated systems can be found everywhere in nature, including the non-linear interaction between optical modes in laser resonators. In this work, we demonstrate artificial neural networks trained to model these complex interactions in the cavity of a Quantum Cascade Random Laser. The neural networks are able to predict modulation schemes for desired laser spectra in real-time. This radically novel approach makes it possible to adapt spectra to individual requirements without the need for lengthy and costly simulation and fabrication iterations. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License.
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    Photochemical CO2 conversion on pristine and Mg-doped gallium nitride (GaN): a comprehensive DFT study based on a cluster model approach
    (Royal Society of Chemistry, 2021-11-23) Butera, Valeria; Detz, Hermann
    The photochemical reduction of carbon dioxide (CO2) into methanol is very appealing since it requires sunlight as the only energy input. However, the development of highly selective and efficient photocatalysts is still very challenging. It has been reported that CO2 can be spontaneously activated on gallium nitride (GaN). Moreover, the photocatalytic activity for CO2 conversion into methanol can be drastically enhanced by incorporating a small amount of Mg dopant. In this work, density functional theory (DFT) based on a cluster model approach has been applied to further explore the photocatalytic activity of bare GaN towards CO2 adsorption and conversion. We extended the investigation of Mg-doping replacing one Ga atom with Mg on three different sites and evaluated the consequent effects on the band gaps and CO2 adsorption energies. Finally, we explore different routes leading to the production of methanol and evaluate the catalytic activity of bare GaN by applying the energetic span model (ESM) in order to identify the rate-determining states which are fundamental for suggesting modifications that can improve the photocatalytic activity of this promising material.
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    Cyclic Carbonate Formation from Epoxides and CO2 Catalyzed by Sustainable Alkali Halide-Glycol Complexes: A DFT Study to Elucidate Reaction Mechanism and Catalytic Activity
    (AMER CHEMICAL SOC, 2020-07-28) Butera, Valeria; Detz, Hermann
    We provide a comprehensive DFT investigation of the mechanistic details of CO2 fixation into styrene oxide to form styrene carbonate, catalyzed by potassium iodide-tetraethylene glycol complex. A detailed view on the intermediate steps of the overall reaction clarifies the role of hydroxyl substances as co-catalysts for the alkali halide-catalyzed cycloaddition. The increase of iodide nucleophilicity in presence of tetraethylene glycol is examined and rationalized by NBO and Hirshfeld charge analysis, and bond distances. We explore how different alkali metal salts and glycols affect the catalytic performance. Our results provide important hints on the synthesis of cyclic carbonates from CO2 and epoxides promoted by alkali halides and glycol complexes, allowing the development of more efficient catalysts.