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23 results on '"Zeisel, Roland"'

1. Interferometric Single-Shot Parity Measurement in an InAs-Al Hybrid Device

Author

Aghaee, Morteza, Ramirez, Alejandro Alcaraz, Alam, Zulfi, Ali, Rizwan, Andrzejczuk, Mariusz, Antipov, Andrey, Astafev, Mikhail, Barzegar, Amin, Bauer, Bela, Becker, Jonathan, Bhaskar, Umesh Kumar, Bocharov, Alex, Boddapati, Srini, Bohn, David, Bommer, Jouri, Bourdet, Leo, Bousquet, Arnaud, Boutin, Samuel, Casparis, Lucas, Chapman, Benjamin James, Chatoor, Sohail, Christensen, Anna Wulff, Chua, Cassandra, Codd, Patrick, Cole, William, Cooper, Paul, Corsetti, Fabiano, Cui, Ajuan, Dalpasso, Paolo, Dehollain, Juan Pablo, de Lange, Gijs, de Moor, Michiel, Ekefjärd, Andreas, Dandachi, Tareq El, Saldaña, Juan Carlos Estrada, Fallahi, Saeed, Galletti, Luca, Gardner, Geoff, Govender, Deshan, Griggio, Flavio, Grigoryan, Ruben, Grijalva, Sebastian, Gronin, Sergei, Gukelberger, Jan, Hamdast, Marzie, Hamze, Firas, Hansen, Esben Bork, Heedt, Sebastian, Heidarnia, Zahra, Zamorano, Jesús Herranz, Ho, Samantha, Holgaard, Laurens, Hornibrook, John, Indrapiromkul, Jinnapat, Ingerslev, Henrik, Ivancevic, Lovro, Jensen, Thomas, Jhoja, Jaspreet, Jones, Jeffrey, Kalashnikov, Konstantin V., Kallaher, Ray, Kalra, Rachpon, Karimi, Farhad, Karzig, Torsten, King, Evelyn, Kloster, Maren Elisabeth, Knapp, Christina, Kocon, Dariusz, Koski, Jonne, Kostamo, Pasi, Kumar, Mahesh, Laeven, Tom, Larsen, Thorvald, Lee, Jason, Lee, Kyunghoon, Leum, Grant, Li, Kongyi, Lindemann, Tyler, Looij, Matthew, Love, Julie, Lucas, Marijn, Lutchyn, Roman, Madsen, Morten Hannibal, Madulid, Nash, Malmros, Albert, Manfra, Michael, Mantri, Devashish, Markussen, Signe Brynold, Martinez, Esteban, Mattila, Marco, McNeil, Robert, Mei, Antonio B., Mishmash, Ryan V., Mohandas, Gopakumar, Mollgaard, Christian, Morgan, Trevor, Moussa, George, Nayak, Chetan, Nielsen, Jens Hedegaard, Nielsen, Jens Munk, Nielsen, William Hvidtfelt Padkær, Nijholt, Bas, Nystrom, Mike, O'Farrell, Eoin, Ohki, Thomas, Otani, Keita, Wütz, Brian Paquelet, Pauka, Sebastian, Petersson, Karl, Petit, Luca, Pikulin, Dima, Prawiroatmodjo, Guen, Preiss, Frank, Morejon, Eduardo Puchol, Rajpalke, Mohana, Ranta, Craig, Rasmussen, Katrine, Razmadze, David, Reentila, Outi, Reilly, David J., Ren, Yuan, Reneris, Ken, Rouse, Richard, Sadovskyy, Ivan, Sainiemi, Lauri, Sanlorenzo, Irene, Schmidgall, Emma, Sfiligoj, Cristina, Shah, Mustafeez Bashir, Simoes, Kevin, Singh, Shilpi, Sinha, Sarat, Soerensen, Thomas, Sohr, Patrick, Stankevic, Tomas, Stek, Lieuwe, Stuppard, Eric, Suominen, Henri, Suter, Judith, Teicher, Sam, Thiyagarajah, Nivetha, Tholapi, Raj, Thomas, Mason, Toomey, Emily, Tracy, Josh, Turley, Michelle, Upadhyay, Shivendra, Urban, Ivan, Van Hoogdalem, Kevin, Van Woerkom, David J., Viazmitinov, Dmitrii V., Vogel, Dominik, Watson, John, Webster, Alex, Weston, Joseph, Winkler, Georg W., Xu, Di, Yang, Chung Kai, Yucelen, Emrah, Zeisel, Roland, Zheng, Guoji, and Zilke, Justin

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

The fusion of non-Abelian anyons or topological defects is a fundamental operation in measurement-only topological quantum computation. In topological superconductors, this operation amounts to a determination of the shared fermion parity of Majorana zero modes. As a step towards this, we implement a single-shot interferometric measurement of fermion parity in indium arsenide-aluminum heterostructures with a gate-defined nanowire. The interferometer is formed by tunnel-coupling the proximitized nanowire to quantum dots. The nanowire causes a state-dependent shift of these quantum dots' quantum capacitance of up to 1 fF. Our quantum capacitance measurements show flux h/2e-periodic bimodality with a signal-to-noise ratio of 1 in 3.7 $\mu$s at optimal flux values. From the time traces of the quantum capacitance measurements, we extract a dwell time in the two associated states that is longer than 1 ms at in-plane magnetic fields of approximately 2 T. These results are consistent with a measurement of the fermion parity encoded in a pair of Majorana zero modes that are separated by approximately 3 $\mu$m and subjected to a low rate of poisoning by non-equilibrium quasiparticles. The large capacitance shift and long poisoning time enable a parity measurement error probability of 1%., Comment: Added data on a second measurement of device A and a measurement of device B, expanded discussion of a trivial scenario. Refs added, author list updated

Published
2024

2. InAs-Al Hybrid Devices Passing the Topological Gap Protocol

Author

Aghaee, Morteza, Akkala, Arun, Alam, Zulfi, Ali, Rizwan, Ramirez, Alejandro Alcaraz, Andrzejczuk, Mariusz, Antipov, Andrey E, Aseev, Pavel, Astafev, Mikhail, Bauer, Bela, Becker, Jonathan, Boddapati, Srini, Boekhout, Frenk, Bommer, Jouri, Hansen, Esben Bork, Bosma, Tom, Bourdet, Leo, Boutin, Samuel, Caroff, Philippe, Casparis, Lucas, Cassidy, Maja, Christensen, Anna Wulf, Clay, Noah, Cole, William S, Corsetti, Fabiano, Cui, Ajuan, Dalampiras, Paschalis, Dokania, Anand, de Lange, Gijs, de Moor, Michiel, Saldaña, Juan Carlos Estrada, Fallahi, Saeed, Fathabad, Zahra Heidarnia, Gamble, John, Gardner, Geoff, Govender, Deshan, Griggio, Flavio, Grigoryan, Ruben, Gronin, Sergei, Gukelberger, Jan, Heedt, Sebastian, Zamorano, Jesús Herranz, Ho, Samantha, Holgaard, Ulrik Laurens, Nielsen, William Hvidtfelt Padkær, Ingerslev, Henrik, Krogstrup, Peter Jeppesen, Johansson, Linda, Jones, Jeffrey, Kallaher, Ray, Karimi, Farhad, Karzig, Torsten, King, Evelyn, Kloster, Maren Elisabeth, Knapp, Christina, Kocon, Dariusz, Koski, Jonne, Kostamo, Pasi, Kumar, Mahesh, Laeven, Tom, Larsen, Thorvald, Li, Kongyi, Lindemann, Tyler, Love, Julie, Lutchyn, Roman, Manfra, Michael, Memisevic, Elvedin, Nayak, Chetan, Nijholt, Bas, Madsen, Morten Hannibal, Markussen, Signe, Martinez, Esteban, McNeil, Robert, Mullally, Andrew, Nielsen, Jens, Nurmohamed, Anne, O'Farrell, Eoin, Otani, Keita, Pauka, Sebastian, Petersson, Karl, Petit, Luca, Pikulin, Dima, Preiss, Frank, Perez, Marina Quintero, Rasmussen, Katrine, Rajpalke, Mohana, Razmadze, Davydas, Reentila, Outi, Reilly, David, Rouse, Richard, Sadovskyy, Ivan, Sainiemi, Lauri, Schreppler, Sydney, Sidorkin, Vadim, Singh, Amrita, Singh, Shilpi, Sinha, Sarat, Sohr, Patrick, Stankevič, Tomaš, Stek, Lieuwe, Suominen, Henri, Suter, Judith, Svidenko, Vicky, Teicher, Sam, Temuerhan, Mine, Thiyagarajah, Nivetha, Tholapi, Raj, Thomas, Mason, Toomey, Emily, Upadhyay, Shivendra, Urban, Ivan, Vaitiekėnas, Saulius, Van Hoogdalem, Kevin, Viazmitinov, Dmitrii V., Waddy, Steven, Van Woerkom, David, Vogel, Dominik, Watson, John, Weston, Joseph, Winkler, Georg W., Yang, Chung Kai, Yau, Sean, Yi, Daniel, Yucelen, Emrah, Webster, Alex, Zeisel, Roland, and Zhao, Ruichen

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We present measurements and simulations of semiconductor-superconductor heterostructure devices that are consistent with the observation of topological superconductivity and Majorana zero modes. The devices are fabricated from high-mobility two-dimensional electron gases in which quasi-one-dimensional wires are defined by electrostatic gates. These devices enable measurements of local and non-local transport properties and have been optimized via extensive simulations to ensure robustness against non-uniformity and disorder. Our main result is that several devices, fabricated according to the design's engineering specifications, have passed the topological gap protocol defined in Pikulin et al. [arXiv:2103.12217]. This protocol is a stringent test composed of a sequence of three-terminal local and non-local transport measurements performed while varying the magnetic field, semiconductor electron density, and junction transparencies. Passing the protocol indicates a high probability of detection of a topological phase hosting Majorana zero modes as determined by large-scale disorder simulations. Our experimental results are consistent with a quantum phase transition into a topological superconducting phase that extends over several hundred millitesla in magnetic field and several millivolts in gate voltage, corresponding to approximately one hundred micro-electron-volts in Zeeman energy and chemical potential in the semiconducting wire. These regions feature a closing and re-opening of the bulk gap, with simultaneous zero-bias conductance peaks at both ends of the devices that withstand changes in the junction transparencies. The extracted maximum topological gaps in our devices are 20-60 $\mu$eV. This demonstration is a prerequisite for experiments involving fusion and braiding of Majorana zero modes., Comment: Final version

Published
2022
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3. Strongly localized carriers in Al-rich AlGaN/AlN single quantum wells grown on sapphire substrates.

Author

Frankerl, Christian, Nippert, Felix, Hoffmann, Marc Patrick, Wang, Heng, Brandl, Christian, Lugauer, Hans-Jürgen, Zeisel, Roland, Hoffmann, Axel, and Davies, Matthew John

Subjects
TIME-resolved spectroscopy, QUANTUM efficiency, QUANTUM wells, SAPPHIRES, TIME-resolved measurements
Abstract

Carrier dynamics in AlGaN-based single quantum well (QW) structures grown on sapphire are studied by means of time-integrated and time-resolved photoluminescence spectroscopy (PL) in a wide temperature range from 5 K to 350 K. The samples cover a broad compositional range, with aluminum contents ranging between 42% and 60% and QW widths between 1.5 nm and 2.5 nm. All samples reveal the characteristic "S"-shape temperature dependence of the PL emission energy as frequently reported in InGaN-based systems, albeit with significantly larger localization strengths of up to 60 meV. It is shown that in the compositional range investigated, carrier localization is determined primarily by the QW width and, in contrast, exhibits a much weaker dependence on aluminum concentration. By the combination of time-integrated and time-resolved PL measurements, the localization of carriers is demonstrated to have a significant impact on the recombination dynamics of AlGaN/AlN QWs grown on sapphire, heavily affecting the internal quantum efficiency and efficiency droop even in standard LED operation conditions. [ABSTRACT FROM AUTHOR]

Published
2020
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4. Challenges for reliable internal quantum efficiency determination in AlGaN-based multi-quantum-well structures posed by carrier transport effects and morphology issues.

Author

Frankerl, Christian, Hoffmann, Marc P., Nippert, Felix, Wang, Heng, Brandl, Christian, Tillner, Nadine, Lugauer, Hans-Jürgen, Zeisel, Roland, Hoffmann, Axel, and Davies, Matthew J.

Subjects
QUANTUM efficiency, OPTICAL measurements, EVALUATION methodology, MORPHOLOGY, UNITS of measurement, EXCITON theory
Abstract

We report on a systematic study of the determination of the internal quantum efficiency (IQE) in AlGaN-based multiple-quantum-well (MQW) structures using different optical evaluation methodologies and experimental conditions, in order to derive a standard set of measurement conditions for reliable IQE determination. Several potential sources of error that may distort the IQE obtained by optical measurements are discussed, such as carrier transport effects, excitation conditions failing to fulfill ideal resonance conditions, and morphology issues. A series of nominally identical AlGaN-based MQW structures is grown on an AlGaN layer separated by an AlN interlayer of varying thickness. The MQW structures are studied both by resonant and quasiresonant photoluminescence spectroscopy, and IQEs are determined via different commonly employed methods. The obtained values are shown to be significantly affected by the employed excitation conditions, as well as the evaluation techniques. In addition, growth morphology issues and carrier transport effects need to be considered in the interpretation of the measured data, with the latter being investigated in greater detail. The results emphasize the need for an appropriate choice of both experimental conditions and evaluation methodology in order to extract reliable and comparable IQE values. [ABSTRACT FROM AUTHOR]

Published
2019
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5. Carrier Dynamics in Al‐Rich AlGaN/AlN Quantum Well Structures Governed by Carrier Localization

Author

Frankerl, Christian, Nippert, Felix, Hoffmann, Marc Patrick, Brandl, Christian, Lugauer, Hans-Jürgen, Zeisel, Roland, Hoffmann, Axel, and Davies, Matthew John

Subjects
ddc:530
Abstract

The carrier dynamics of Al‐rich AlGaN/AlN quantum well (QW) structures in the presence of strong carrier localization is reported. Excitation density‐dependent photoluminescence (PL) measurements at low temperatures reveal a clear correlation between the onset of efficiency droop and the broadening of the time‐integrated PL spectra. While the droop onset is heavily impacted by the localization strength, the PL emission broadening is observed almost exclusively on the high energy side of the emission spectrum. Spectrally resolved PL decay transient measurements reveal a strong dependency of the carrier lifetimes on the emission photon energy across the spectrum, consistent with a distribution of localized states, as well as on the temperature, depending on the localization strength of the investigated structure. The characteristic “S”‐shaped temperature dependence of the PL emission energy is shown to be directly correlated to the thermal redistribution of carriers between localized states. Based on these findings, the role of carrier localization in the recombination processes in AlGaN QW structures is underlined and its implications for efficiency droop are discussed.

Published
2020

6. Point defect-induced UV-C absorption in aluminum nitride epitaxial layers grown on sapphire substrates by metal-organic chemical vapor deposition

Author

Tillner, Nadine, Frankerl, Christian, Nippert, Felix, Davies, Matthew J., Brandl, Christian, Lösing, Rainer, Mandl, Martin, Lugauer, Hans-Jürgen, Zeisel, Roland, Hoffmann, Axel, Waag, Andreas, and Hoffmann, Marc Patrick

Subjects
epitaxy, point defects, 535 Licht, Infrarot- und Ultraviolettphänomene, ddc:535, absorption, AlN, metal-organic chemical vapor deposition
Abstract

Herein, the optical properties of aluminum nitride (AlN) epitaxial layers grown on sapphire substrates by metal-organic chemical vapor deposition (MOCVD) are reported. The structures investigated in this study are grown at highly different degrees of supersaturation in the MOCVD process. In addition, both pulsed and continuous growth conditions are employed and AlN is deposited on nucleation layers favoring different polarities. The samples are investigated by photoluminescence (PL), photoluminescence excitation (PLE), and absorption spectroscopy and are found to vary significantly in absorption and emission characteristics. Two distinct absorption bands in the UV-C spectral range are observed and examined in greater detail, with either giving rise to a significant absorption coefficient of around 1000 cm−1. The corresponding defect transitions are identified by PL spectroscopy. Combined with secondary-ion mass spectrometry (SIMS) measurements, these absorption bands are allocated to the incorporation of carbon and oxygen impurities, depending on the applied growth conditions. Furthermore, similarities with other epitaxial growth techniques serving as basis for UV-C applications are highlighted. These results are highly relevant for a better understanding of absorption issues in AlN templates grown by various deposition techniques. In addition, consequences for the growth of efficient UV-C devices by MOCVD on sapphire substrates are outlined.

Published
2020

7. Influence of the Growth Substrate on the Internal Quantum Efficiency of AlGaN/AlN Multiple Quantum Wells Governed by Carrier Localization

Author

Jacopin, Gwénolé, primary, Frankerl, Christian, additional, Tillner, Nadine, additional, Davies, Matthew John, additional, Rossbach, Georg, additional, Brandl, Christian, additional, Hoffmann, Marc Patrick, additional, Zeisel, Roland, additional, Hoffmann, Axel, additional, and Lugauer, Hans-Jürgen, additional

Published
2020
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9. Point Defect‐Induced UV‐C Absorption in Aluminum Nitride Epitaxial Layers Grown on Sapphire Substrates by Metal‐Organic Chemical Vapor Deposition

Author

Tillner, Nadine, primary, Frankerl, Christian, additional, Nippert, Felix, additional, Davies, Matthew J., additional, Brandl, Christian, additional, Lösing, Rainer, additional, Mandl, Martin, additional, Lugauer, Hans-Jürgen, additional, Zeisel, Roland, additional, Hoffmann, Axel, additional, Waag, Andreas, additional, and Hoffmann, Marc Patrick, additional

Published
2020
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13. Influence of the Growth Substrate on the Internal Quantum Efficiency of AlGaN/AlN Multiple Quantum Wells Governed by Carrier Localization.

Author

Jacopin, Gwénolé, Frankerl, Christian, Tillner, Nadine, Davies, Matthew John, Rossbach, Georg, Brandl, Christian, Hoffmann, Marc Patrick, Zeisel, Roland, Hoffmann, Axel, and Lugauer, Hans-Jürgen

Subjects
QUANTUM wells, QUANTUM efficiency, CATHODOLUMINESCENCE, LIGHT emitting diodes, ATOMIC force microscopy, POINT defects, PHOTOLUMINESCENCE
Abstract

The influence of the growth substrate on the internal quantum efficiency (IQE) of deep ultraviolet light‐emitting diodes is studied. Two nominally identical Al‐rich AlGaN/AlN multi‐quantum‐well (MQW) structures grown by metal–organic vapor phase epitaxy (MOVPE) on different substrates are investigated. The first MQW structure is grown on a native AlN substrate, whereas the second one is deposited on an AlN template on sapphire. By the combination of atomic force microscopy (AFM), photoluminescence (PL), and cathodoluminescence (CL) spectroscopy, it is demonstrated that the dislocation‐mediated spiral growth of MQWs on sapphire results in the more efficient localization of carriers. This effect helps to prevent nonradiative carrier recombination at point defects, improving the IQE of the structure. [ABSTRACT FROM AUTHOR]

Published
2021
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17. Optoelectronic Properties of Defects in Diamond and AlGaN Alloys

Author

Zeisel, Roland, Stutzmann, Martin (Prof. Dr.), Gross, Rudolf (Prof. Dr.), and Koch, Frederik (Prof. Ph.D.)

Subjects
Physik, Diamant, AlN, GaN, Defekte, DLTS, Photoleitung, DX, Implantation, ddc:530, diamond, defects, photoconductivity, implantation
Abstract

Die Dotiereigenschaften von Bor und Lithium in Diamant wurden mittels Kapazitäts- Spannungsmessungen und spektral aufgelöster Photoleitung charakterisiert. Zusätzlich wurde eine Passivierung von Bor-Akzeptoren durch Wasserstoff nachgewiesen und das thermische Aufbrechen der B-H-Bindungen untersucht. Mittels transienter Kapazitätsspektroskopie wurde ein implantationsinduzierter Defekt in Diamant 1.28 eV über dem Valenzband nachgewiesen und sein Ausheilverhalten studiert. Durch spektral aufgelöste Photoleitung in Kombination mit Elektronenspinresonanz konnte gezeigt werden, daß Silizium in AlGaN Legierungen mit hohem Al-Gehalt vom normalen effektiv-Masse Verhalten abweicht und ein $DX$-Zentrum bildet.

Published
2007

18. Analysis and in situ observation of humidity dependent atomic layer deposited-Al2O3 degradation.

Author

Rückerl, Andreas, Huppmann, Sophia, Mandl, Martin, Katz, Simeon, and Zeisel, Roland

Subjects
ALUMINUM oxide, HUMIDITY, ATOMIC layer deposition, CHEMICAL decomposition, HIGH temperatures, HYDROXYL group
Abstract

The degradation of atomic layer deposited aluminum oxide (ALD-Al2O3) at high temperature and high humidity was investigated. The intrinsic hydroxyl concentration of as-deposited ALD-Al2O3 was evaluated using a temperature dependent deposition study and its impact on degradation behavior was analyzed. In addition, the degradation of ALD-Al2O3 was monitored in situ using a plate capacitor with ALD-Al2O3 as dielectric. A model for the ALD-Al2O3 degradation mechanism was proposed based on the penetration of water molecules into the ALD-Al2O3 and on the formation of aluminum hydroxide. Two parameters, delay-time (time till a change in capacitance occurs) and wetting speed (speed of molecular water penetration into the ALD-Al2O3), were extracted from the capacitance measurements in order to evaluate the dependence of ALD-Al2O3 degradation on temperature and humidity. [ABSTRACT FROM AUTHOR]

Published
2017
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19. Optoelectronic Properties of Defects in Diamond and AlGaN Alloys

Author

Stutzmann, Martin (Prof. Dr.), Gross, Rudolf (Prof. Dr.), Koch, Frederik (Prof. Ph.D.), Zeisel, Roland, Stutzmann, Martin (Prof. Dr.), Gross, Rudolf (Prof. Dr.), Koch, Frederik (Prof. Ph.D.), and Zeisel, Roland

Abstract

Die Dotiereigenschaften von Bor und Lithium in Diamant wurden mittels Kapazitäts- Spannungsmessungen und spektral aufgelöster Photoleitung charakterisiert. Zusätzlich wurde eine Passivierung von Bor-Akzeptoren durch Wasserstoff nachgewiesen und das thermische Aufbrechen der B-H-Bindungen untersucht. Mittels transienter Kapazitätsspektroskopie wurde ein implantationsinduzierter Defekt in Diamant 1.28 eV über dem Valenzband nachgewiesen und sein Ausheilverhalten studiert. Durch spektral aufgelöste Photoleitung in Kombination mit Elektronenspinresonanz konnte gezeigt werden, daß Silizium in AlGaN Legierungen mit hohem Al-Gehalt vom normalen effektiv-Masse Verhalten abweicht und ein $DX$-Zentrum bildet.

Published
2007

23. Towards quantification of the crucial Impact of auger recombination for the Efficiency droop in (AlInGa)N Quantum well structures

Author

Nirschl, Anna, Binder, Michael, Schmid, Marina, Pietzonka, Ines, Lugauer, Hans-Jürgen, Zeisel, Roland, Sabathil, Matthias, Bougeard, Dominique, and Galler, Bastian

Subjects
LIGHT-EMITTING-DIODES, GAN, 530 Physik, 3. Good health
Abstract

Recent experimental investigations on the reduction of internal quantum efficiency with increasing current density in (AlInGa)N quantum well structures show that Auger recombination is a significant contributor to the so-called "droop" phenomenon. Using photoluminescence (PL) test structures, we find Auger processes are responsible for at least 15 % of the measured efficiency droop. Furthermore, we confirm that electron-electron-hole (nnp) is stronger than electron-hole-hole (npp) Auger recombination in standard LEDs. The ratio of respective Auger coefficients is determined to be in the range 1 < C-nnp = C-npp

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