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1. Femtosecond pump-probe absorption edge spectroscopy of cubic GaN

Author

Baron, Elias, Goldhahn, Rüdiger, Espinoza, Shirly, Zahradník, Martin, Rebarz, Mateusz, Andreasson, Jakob, Deppe, Michael, As, Donat J., and Feneberg, Martin

Subjects
Condensed Matter - Materials Science
Abstract

Time-dependent femtosecond pump-probe spectroscopic ellipsometry studies on zincblende gallium-nitride (zb-GaN) are performed and analyzed between 2.9-3.7eV. An ultra-fast change of the absorption onset (3.23eV for zb-GaN) is observed by investigating the imaginary part of the dielectric function. The 266nm (4.66eV) pump pulses induce a large free-carrier concentration up to $4\times 10^{20}$cm$^{-3}$, influencing the transition energy between conduction and valence bands due to many-body effects, like band filling and band gap renormalization, up to $\approx$500meV. Additionally, the absorption of the pump-beam creates a free-carrier profile within the 605nm zb-GaN layer. This leads to varying optical properties from sample surface to substrate, which are taken into account by grading analysis for an accurate description of the experimental data. A temporal resolution of 100fs allows in-depth investigations of occurring ultra-fast relaxation and recombination processes. We provide a quantitative description of the free-carrier concentration and absorption onset at the sample surface as a function of relaxation, recombination, and diffusion yielding a characteristic relaxation time of 0.19ps and a recombination time of 26.1ps.

Published
2022

2. Extremely low energy ARPES of quantum well states in cubic-GaN/AlN and GaAs/GaAlAs heterostructures

Author

Hajlaoui, Mahdi, Ponzoni, Stefano, Deppe, Michael, Henksmeier, Tobias, As, Donat Josef, Reuter, Dirk, Zentgraf, Thomas, Schneider, Claus Michael, and Cinchetti, Mirko

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science, Physics - Applied Physics
Abstract

Quantum well (QW) heterostructures have been extensively used for the realization of a wide range of optical and electronic devices. Exploiting their potential for further improvement and development requires a fundamental understanding of their electronic structure. So far, the most commonly used experimental techniques for this purpose have been all-optical spectroscopy methods that, however, are generally averaged in momentum space. Additional information can be gained by angle-resolved photoelectron spectroscopy (ARPES), which measures the electronic structure with momentum resolution. Here we report on the use of extremely low energy ARPES (photon energy $\sim$ 7 eV) to increase its depth sensitivity and access buried QW states, located at 3 nm and 6 nm below the surface of cubic-GaN/AlN and GaAs/AlGaAs heterostructures, respectively. We find that the QW states in cubic-GaN/AlN can indeed be observed, but not their energy dispersion because of the high surface roughness. The GaAs/AlGaAs QW states, on the other hand, are buried too deep to be detected by extremely low energy ARPES. Since the sample surface is much flatter, the ARPES spectra of the GaAs/AlGaAs show distinct features in momentum space, which can be reconducted to the band structure of the topmost surface layer of the QW structure. Our results provide important information about the samples' properties required to perform extremely low energy ARPES experiments on electronic states buried in semiconductor heterostructures.

Published
2021

3. Widespread white matter microstructural abnormalities in bipolar disorder: evidence from mega- and meta-analyses across 3033 individuals

Author

Favre, Pauline, Pauling, Melissa, Stout, Jacques, Hozer, Franz, Sarrazin, Samuel, Abé, Christoph, Alda, Martin, Alloza, Clara, Alonso-Lana, Silvia, Andreassen, Ole A, Baune, Bernhard T, Benedetti, Francesco, Busatto, Geraldo F, Canales-Rodríguez, Erick J, Caseras, Xavier, Chaim-Avancini, Tiffany Moukbel, Ching, Christopher RK, Dannlowski, Udo, Deppe, Michael, Eyler, Lisa T, Fatjo-Vilas, Mar, Foley, Sonya F, Grotegerd, Dominik, Hajek, Tomas, Haukvik, Unn K, Howells, Fleur M, Jahanshad, Neda, Kugel, Harald, Lagerberg, Trine V, Lawrie, Stephen M, Linke, Julia O, McIntosh, Andrew, Melloni, Elisa MT, Mitchell, Philip B, Polosan, Mircea, Pomarol-Clotet, Edith, Repple, Jonathan, Roberts, Gloria, Roos, Annerine, Rosa, Pedro GP, Salvador, Raymond, Sarró, Salvador, Schofield, Peter R, Serpa, Mauricio H, Sim, Kang, Stein, Dan J, Sussmann, Jess E, Temmingh, Henk S, Thompson, Paul M, Verdolini, Norma, Vieta, Eduard, Wessa, Michele, Whalley, Heather C, Zanetti, Marcus V, Leboyer, Marion, Mangin, Jean-François, Henry, Chantal, Duchesnay, Edouard, and Houenou, Josselin

Subjects
Biological Psychology, Biomedical and Clinical Sciences, Psychology, Brain Disorders, Serious Mental Illness, Neurosciences, Bipolar Disorder, Biomedical Imaging, Mental Health, Clinical Research, Mental health, Adult, Brain, Corpus Callosum, Diffusion Tensor Imaging, Female, Humans, Male, Neural Pathways, White Matter, ENIGMA Bipolar Disorder Working Group, Medical and Health Sciences, Psychology and Cognitive Sciences, Psychiatry, Biological psychology
Abstract

Fronto-limbic white matter (WM) abnormalities are assumed to lie at the heart of the pathophysiology of bipolar disorder (BD); however, diffusion tensor imaging (DTI) studies have reported heterogeneous results and it is not clear how the clinical heterogeneity is related to the observed differences. This study aimed to identify WM abnormalities that differentiate patients with BD from healthy controls (HC) in the largest DTI dataset of patients with BD to date, collected via the ENIGMA network. We gathered individual tensor-derived regional metrics from 26 cohorts leading to a sample size of N = 3033 (1482 BD and 1551 HC). Mean fractional anisotropy (FA) from 43 regions of interest (ROI) and average whole-brain FA were entered into univariate mega- and meta-analyses to differentiate patients with BD from HC. Mega-analysis revealed significantly lower FA in patients with BD compared with HC in 29 regions, with the highest effect sizes observed within the corpus callosum (R2 = 0.041, Pcorr

Published
2019

4. Correction: Widespread white matter microstructural abnormalities in bipolar disorder: evidence from mega- and meta-analyses across 3033 individuals

Author

Favre, Pauline, Pauling, Melissa, Stout, Jacques, Hozer, Franz, Sarrazin, Samuel, Abé, Christoph, Alda, Martin, Alloza, Clara, Alonso-Lana, Silvia, Andreassen, Ole A, Baune, Bernhard T, Benedetti, Francesco, Busatto, Geraldo F, Canales-Rodríguez, Erick J, Caseras, Xavier, Chaim-Avancini, Tiffany Moukbel, Ching, Christopher RK, Dannlowski, Udo, Deppe, Michael, Eyler, Lisa T, Fatjo-Vilas, Mar, Foley, Sonya F, Grotegerd, Dominik, Hajek, Tomas, Haukvik, Unn K, Howells, Fleur M, Jahanshad, Neda, Kugel, Harald, Lagerberg, Trine V, Lawrie, Stephen M, Linke, Julia O, McIntosh, Andrew, Melloni, Elisa MT, Mitchell, Philip B, Polosan, Mircea, Pomarol-Clotet, Edith, Repple, Jonathan, Roberts, Gloria, Roos, Annerine, Rosa, Pedro GP, Salvador, Raymond, Sarró, Salvador, Schofield, Peter R, Serpa, Mauricio H, Sim, Kang, Stein, Dan J, Sussmann, Jess E, Temmingh, Henk S, Thompson, Paul M, Verdolini, Norma, Vieta, Eduard, Wessa, Michele, Whalley, Heather C, Zanetti, Marcus V, Leboyer, Marion, Mangin, Jean-François, Henry, Chantal, Duchesnay, Edouard, and Houenou, Josselin

Subjects
Biological Psychology, Biomedical and Clinical Sciences, Neurosciences, Psychology, ENIGMA Bipolar Disorder Working Group, Medical and Health Sciences, Psychology and Cognitive Sciences, Psychiatry, Biological psychology
Abstract

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Published
2019

5. Time-resolved pump–probe spectroscopic ellipsometry of cubic GaN II: Absorption edge shift with gain and temperature effects.

Author

Baron, Elias, Goldhahn, Rüdiger, Espinoza, Shirly, Zahradník, Martin, Rebarz, Mateusz, Andreasson, Jakob, Deppe, Michael, As, Donat J., and Feneberg, Martin

Subjects
TEMPERATURE effect, GALLIUM nitride, ELLIPSOMETRY, CONDUCTION bands, DIELECTRIC function, ION recombination
Abstract

We recently published a study concerning femtosecond pump–probe absorption edge spectroscopy of cubic GaN (fundamental bandgap: 3.23 eV), resulting in the transient dielectric function. In the present study, we continue our investigations of those pump–probe measurements by determining the time-dependent transition energy at the Fermi-vector between the conduction and valence bands. The generation of electron–hole pairs by the 266 nm pump-beam (4.66 eV) shifts the absorption edge by ≈ 500 meV within 1 ps due to many-body effects like band-filling and bandgap renormalization. Modeling this ultra-fast change is achieved by converting the transition energies into free-carrier concentrations, assuming the electron contributions to be dominant. We consider the relaxation, recombination, and diffusion of those free-carriers as well as either an additional gain-recombination or temperature effects. This allows for describing the transition energies on short time scales. Both models yield similar values for the characteristic relaxation time (≈ 0.21 ps), recombination time (≈ 25 ps), and diffusion coefficient (≈ 1 cm 2 /s). [ABSTRACT FROM AUTHOR]

Published
2023
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6. Time-resolved pump–probe spectroscopic ellipsometry of cubic GaN. I. Determination of the dielectric function.

Author

Baron, Elias, Goldhahn, Rüdiger, Espinoza, Shirly, Zahradník, Martin, Rebarz, Mateusz, Andreasson, Jakob, Deppe, Michael, As, Donat J., and Feneberg, Martin

Subjects
DIELECTRIC function, ELLIPSOMETRY, CONDUCTION bands, VALENCE bands, GALLIUM nitride, OXYGEN carriers, CARRIER density
Abstract

An ultra-fast change of the absorption onset for zincblende gallium-nitride (zb-GaN) (fundamental bandgap: 3.23 eV) is observed by investigating the imaginary part of the dielectric function using time-dependent femtosecond pump–probe spectroscopic ellipsometry between 2.9 and 3.7 eV. The 266 nm (4.66 eV) pump pulses induce a large electron–hole pair concentration up to 4 × 10 20 cm − 3 , which shift the transition energy between conduction and valence bands due to many-body effects up to ≈ 500 meV. Here, the absorption onset increases due to band filling while the bandgap renormalization at the same time decreases the bandgap. Additionally, the absorption of the pump-beam creates a free-carrier profile within the 605 nm zb-GaN layer with high free-carrier concentrations at the surface, and low concentrations at the interface to the substrate. This leads to varying optical properties from the sample surface (high transition energy) to substrate (low transition energy), which are taken into account by grading analysis for an accurate description of the experimental data. For this, a model describing the time- and position-dependent free-carrier concentration is formulated by considering the relaxation, recombination, and diffusion of those carriers. We provide a quantitative analysis of optical experimental data (ellipsometric angles Ψ and Δ) as well as a plot for the time-dependent change of the imaginary part of the dielectric function. [ABSTRACT FROM AUTHOR]

Published
2023
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7. Interleukin-6 Receptor Blockade in Treatment-Refractory MOG-IgG–Associated Disease and Neuromyelitis Optica Spectrum Disorders

Author

Ringelstein, Marius, Ayzenberg, Ilya, Lindenblatt, Gero, Fischer, Katinka, Gahlen, Anna, Novi, Giovanni, Hayward-Könnecke, Helen, Schippling, Sven, Rommer, Paulus S., Kornek, Barbara, Zrzavy, Tobias, Biotti, Damien, Ciron, Jonathan, Audoin, Bertrand, Berthele, Achim, Giglhuber, Katrin, Zephir, Helene, Kümpfel, Tania, Berger, Robert, Röther, Joachim, Häußler, Vivien, Stellmann, Jan-Patrick, Whittam, Daniel, Jacob, Anu, Kraemer, Markus, Gueguen, Antoine, Deschamps, Romain, Bayas, Antonios, Hümmert, Martin W., Trebst, Corinna, Haarmann, Axel, Jarius, Sven, Wildemann, Brigitte, Grothe, Matthias, Siebert, Nadja, Ruprecht, Klemens, Paul, Friedemann, Collongues, Nicolas, Marignier, Romain, Levy, Michael, Karenfort, Michael, Deppe, Michael, Albrecht, Philipp, Hellwig, Kerstin, Gold, Ralf, Hartung, Hans-Peter, Meuth, Sven G., Kleiter, Ingo, and Aktas, Orhan

Published
2022
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8. Longitudinal optic neuritis-unrelated visual evoked potential changes in NMO spectrum disorders

Author

Ringelstein, Marius, Harmel, Jens, Zimmermann, Hanna, Brandt, Alexander U., Paul, Friedemann, Haarmann, Axel, Buttmann, Mathias, Hümmert, Martin W., Trebst, Corinna, Schroeder, Christoph, Ayzenberg, Ilya, Kleiter, Ingo, Hellwig, Kerstin, Havla, Joachim, Kümpfel, Tania, Jarius, Sven, Wildemann, Brigitte, Rommer, Paulus, Weber, Martin S., Pellkofer, Hannah, Röpke, Luise, Geis, Christian, Retzlaff, Nele, Zettl, Uwe, Deppe, Michael, Klotz, Luisa, Young, Kim, Stellmann, Jan-Patrick, Kaste, Matthias, Kermer, Pawel, Marouf, Wael, Lauda, Florian, Tumani, Hayrettin, Graf, Jonas, Klistorner, Alexander, Hartung, Hans-Peter, Aktas, Orhan, and Albrecht, Philipp

Published
2020
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12. Neurochondrin is a neuronal target antigen in autoimmune cerebellar degeneration

Author

Miske, Ramona, Gross, Catharina C., Scharf, Madeleine, Golombeck, Kristin S., Hartwig, Marvin, Bhatia, Urvashi, Schulte-Mecklenbeck, Andreas, Bönte, Kathrin, Strippel, Christine, Schöls, Ludger, Synofzik, Matthis, Lohmann, Hubertus, Dettmann, Inga Madeleine, Deppe, Michael, Mindorf, Swantje, Warnecke, Tobias, Denno, Yvonne, Teegen, Bianca, Probst, Christian, Brakopp, Stefanie, Wandinger, Klaus-Peter, Wiendl, Heinz, Stöcker, Winfried, Meuth, Sven G., Komorowski, Lars, and Melzer, Nico

Published
2017
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21. Individual white matter fractional anisotropy analysis on patients with MRI negative partial epilepsy

Author

Duning, Thomas, Kellinghaus, Christoph, Mohammadi, Siawoosh, Schiffbauer, Hagen, Keller, Simon, Ringelstein, E. Bernd, Knecht, Stefan, and Deppe, Michael

Subjects
Anisotropy -- Analysis, Anisotropy -- Demographic aspects, Anisotropy -- Research, Magnetic resonance imaging -- Usage, Magnetic resonance imaging -- Research, Partial epilepsy -- Diagnosis, Partial epilepsy -- Research, Health, Psychology and mental health
Published
2010

24. Germanium doping of aluminum-containing cubic group III-nitride heterostructures

Author

Deppe, Michael

Abstract

Die Gruppe III-Nitride sind ein wichtiges Halbleitermaterialsystem mit vielen Anwendungen in der Optoelektronik und in der Leistungselektronik. Insbesondere für optoelektronische Anwendungen ist die metastabile Zinkblende-Phase eine vielversprechende Alternative zu der üblicherweise verwendeten Wurtzit-Phase, da hier Polarisationsfelder, die die Rekombinationseffizienz beeinträchtigen, nicht vorhanden sind. Die Herstellung der meisten Bauelemente erfordert eine präzise Kontrolle der p- und n-Typ-Dotierung. Für die n-Typ-Dotierung wird üblicherweise Si verwendet, das jedoch bei hohen Dotierungskonzentrationen für eine Zugverspannung sorgt und dadurch die Kristallqualität verschlechtert. Kürzlich wurde berichtet, dass Ge eine geeignete Alternative zu Si für die n-Typ-Dotierung von Nitriden in der Wurtzitstruktur ist. Hohe Donatorkonzentrationen konnten erreicht werden, ohne die strukturelle Qualität der Schichten zu beeinträchtigen. In dieser Arbeit wird Ge als Donator für GaN und Al[]Ga[1]N bis zu = 0,6 in der Zinkblende-Struktur untersucht. Es wurden Ge- und Si dotierte GaN-Schichten mit Dotierkonzentrationen über mehrere Größenordnungen hergestellt und hinsichtlich ihrer optischen, strukturellen und elektrischen Eigenschaften untersucht. Die maximal erreichbaren freien Elektronenkonzentrationen liegen bei 3.710^20 cm^3 bzw. 4.310^20 cm^3 für die Ge- und Si-Dotierung. The group III-nitrides are an important semiconductor material system with many applications in optoelectronics and power devices. Especially for optoelectronic applications, the metastable zinc blende phase is a promising alternative to the commonly employed wurtzite phase, as polarization fields which impair the recombination efficiency are absent here. The fabrication of most devices requires precise control of p- and n-type doping. For n-type doping mostly Si is used, which however introduces tensile strain at high doping concentrations and deteriorates the crystal quality. Recently, Ge was found to be a well-suited alternative to Si for n-type doping of wurtzite nitrides, which allows for high donor concentrations without impairing the structural quality. In this work Ge is investigated as a donor in zinc blende GaN and Al[]Ga[1]N up to = 0.6. Ge- and Si-doped GaN layers with doping levels spanning over several orders of magnitude were fabricated and investigated regarding their optical, structural, and electrical properties. The maximum achievable free electron concentrations are 3.710^20 cm^3 and 4.310^20 cm^3 for Ge- and Si-doping, respectively. von Michael Deppe Tag der Verteidigung: 03.09.2020 Universität Paderborn, Dissertation, 2020

Published
2020
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36. Author response: Longitudinal optic neuritis-unrelated visual evoked potential changes in NMO spectrum disorders

Author

Ringelstein, Marius, primary, Harmel, Jens, additional, Zimmermann, Hanna, additional, Brandt, Alexander U., additional, Paul, Friedemann, additional, Haarmann, Axel, additional, Buttmann, Mathias, additional, Hümmert, Martin W., additional, Trebst, Corinna, additional, Schroeder, Christoph, additional, Ayzenberg, Ilya, additional, Kleiter, Ingo, additional, Hellwig, Kerstin, additional, Havla, Joachim, additional, Kümpfel, Tania, additional, Jarius, Sven, additional, Wildemann, Brigitte, additional, Rommer, Paulus, additional, Weber, Martin, additional, Pellkofer, Hannah, additional, Röpke, Luise, additional, Geis, Christian, additional, Retzlaff, Nele, additional, Zettl, Uwe, additional, Deppe, Michael, additional, Klotz, Luisa, additional, Young, Kim, additional, Stellmann, Jan-Patrick, additional, Kaste, Matthias, additional, Kermer, Pawel, additional, Marouf, Wael, additional, Lauda, Florian, additional, Tumani, Hayrettin, additional, Graf, Jonas, additional, Klistorner, Sasha, additional, Hartung, Hans-Peter, additional, Aktas, Orhan, additional, and Albrecht, Philipp, additional

Published
2020
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44. Photoluminescence line shape analysis of highly n‐type doped zincblende GaN

Author

Baron, Elias, Goldhahn, Rüdiger, Deppe, Michael, As, Donat J., and Feneberg, Martin

Subjects
Zincblende GaN, Burstein–Moss shift, Photoluminescence
Abstract

An investigation of different n-type doped zincblende gallium nitride thin films measured by photoluminescence from 7 K to room temperature is presented. The spectra change with increasing free-carrier concentration due to many-body effects such as the Burstein–Moss shift and band-gap renormalization. The samples are grown by molecular beam epitaxy on a 3C-SiC/Si (001) substrate, and a free-carrier concentration above 1020 cm 3 is achieved by introducing germanium as a donor. The analysis of the measured spectra by a line-shape fit yields different transition processes for different doping concentrations and temperatures, such as a band–band transition and a band–acceptor transition. The conduction band dispersion of Kane’s model is perfectly suited to explain the experimental data quantitatively.

Published
2019
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