Technische Universität Berlin

13074 Items

Recent Submissions
MODUS-COVID Bericht vom 20.01.2022

Müller, Sebastian Alexander ; Charlton, William ; Conrad, Natasa Djurdjevac ; Ewert, Ricardo ; Paltra, Sydney ; Rakow, Christian ; Wulkow, Hanna ; Conrad, Tim ; Schütte, Christof ; Nagel, Kai (2022-01-20)

Die Mobilität ist über die Weihnachtsferien sowohl in Berlin als auch in Köln deutlich zurückgegangen. Im Januar hat sich die aushäusig verbrachte Zeit wieder erhöht; das aktuelle Niveau ist jedoch immer noch unter dem Niveau vor den Ferien (vgl. Abschnitt 2, S.1). Die Omikron-Variante ist bekanntlich in den meisten Bundesländern inzwischen dominant, und führt zu stark ansteigenden Inzidenzen,...

Decay dynamics of neutral and charged excitonic complexes in single InAs∕GaAs quantum dots

Feucker, M. ; Seguin, Robert ; Rodt, Sven ; Hoffmann, Axel ; Bimberg, Dieter (2008-02-14)

Systematic time-resolved measurements on neutral and charged excitonic complexes (𝑋, 𝑋𝑋, 𝑋+, and 𝑋𝑋+) of 26 different single InAs∕GaAs quantum dots are reported. The ratios of the decay times are discussed in terms of the number of transition channels determined by the excitonic fine structure and a specific transition time for each channel. The measured ratio for the neutral complexes is...

A write time of 6ns for quantum dot–based memory structures

Geller, Martin ; Marent, A. ; Nowozin, Tobias ; Bimberg, Dieter ; Akçay, N. ; Öncan, N. (2008-03-04)

The concept of a memory device based on self-organized quantum dots (QDs) is presented, enabling extremely fast write times, limited only by the charge carrier relaxation time being in the picosecond range. For a first device structure with embedded InAs∕GaAs QDs, a write time of 6ns is demonstrated. A similar structure containing GaSb∕GaAs QDs shows a write time of 14ns. These write times are ...

High-power semiconductor disk laser based on InAs∕GaAs submonolayer quantum dots

Germann, Tim David ; Strittmatter, André ; Pohl, J. ; Pohl, Udo W. ; Bimberg, Dieter ; Rautiainen, Jussi ; Guina, Mircea ; Okhotnikov, Oleg G. (2008-03-13)

An optically pumped semiconductor disk laser using submonolayer quantum dots (SML QDs) as gain medium is demonstrated. High-power operation is achieved with stacked InAs∕GaAs SML QDs grown by metal-organic vapor-phase epitaxy. Each SML-QD layer is formed from tenfold alternate depositions of nominally 0.5 ML InAs and 2.3 ML GaAs. Resonant periodic gain from a 13-fold nonuniform stack design of ...

40 GHz small-signal cross-gain modulation in 1.3𝜇m quantum dot semiconductor optical amplifiers

Meuer, Christian ; Kim, Joungmok ; Laemmlin, M. ; Liebich, S. ; Bimberg, Dieter ; Capua, Amir ; Eisenstein, Gadi ; Bonk, René ; Vallaitis, Thomas ; Leuthold, Juerg ; Kovsh, A. R. ; Krestnikov, Igor L. (2008-08-06)

Small-signal cross-gain modulation of quantum dot based semiconductor optical amplifiers (QD SOAs), having a dot-in-a-well structure, is presented, demonstrating superiority for ultrahigh bit rate wavelength conversion. Optimization of the QD SOA high speed characteristics via bias current and optical pump power is presented and a small-signal 3 dB bandwidth exceeding 40 GHz is demonstrated. Th...

Systemtechnische Bearbeitungs- und Darstellungsmethodik multidimensionaler Prozesse

Schönauer, Moritz (2022)

Aufgrund der disruptiven Umstellung ihrer Produktpalette auf die Elektromobilität, gepaart mit dem Wettlauf aller Marktteilnehmer um das erste serientaugliche autonom fahrende Fahrzeug, haben im Speziellen in der Automobilindustrie die Auswirkungen der vierten industriellen Revolution bereits Einzug ins unmittelbare Tagesgeschäft gehalten. Durch diese Neufokussierungen und tiefgreifenden Umbrüc...

Efficient pareto frontier algorithms for computing structured signal representations

Vural, Metin (2022)

ℓp-norm minimization plays a significant role in a variety of disciplines. It is not only important for the signal recovery in compressed sensing but also beneficial for finding meaningful signal representations as for the sparse and anti-sparse coding related applications. Therefore, minimizing ℓp-norms in an efficient manner sparked interest in a variety of works. This thesis is concerned wit...

From terahertz to X-ray

Christiansen, Dominik (2022)

The recent rise of two-dimensional materials attracted a tremendous amount of interest in the fields of photonics and optoelectronics, as they are promising candidates for next-generation devices. Materials, which are under extensive investigation, are graphene and monolayer transition-metal dichalcogenides (TMDC). While graphene is a semi-metal, certain monolayer TMDCs are semiconductors exhib...

Towing tank experiments on the aerodynamic drag of trains

Tschepe, Jonathan (2022)

Due to increasing requirements regarding low energy consumption, the aerodynamic drag of rail vehicles has become more and more important in recent years. Many studies have dealt with the aerodynamic drag in the last decades and have provided a good understanding of fundamentals and boundary conditions. A variety of experimental methods and measurement techniques have been used in this context....

Temperature-stable operation of a quantum dot semiconductor disk laser

Germann, Tim David ; Strittmatter, André ; Pohl, J. ; Pohl, Udo W. ; Bimberg, Dieter ; Rautiainen, J. ; Guina, M. ; Okhotnikov, O. G. (2008-08-05)

We demonstrate temperature-independent output characteristics of an optically pumped semiconductor disk laser (SDL) based on quantum dots (QDs) grown in the Stranski-Krastanow regime. The gain structure consists of a stack of 7×3 QD layers, each threefold group being located at an optical antinode position. The SDL emits at 1210nm independent of the pump power density. Threshold and differentia...

Ultrahigh-brightness 850 nm GaAs/AlGaAs photonic crystal laser diodes

Posilović, Kristijan ; Kettler, T. ; Shchukin, V. A. ; Ledentsov, Nikolai N. ; Pohl, Udo W. ; Bimberg, Dieter ; Fricke, J. ; Ginolas, A. ; Erbert, G. ; Tränkle, G. ; Jönsson, J. ; Weyers, Markus (2008-12-01)

One-dimensional photonic crystal lasers emitting in the 850 nm range show high internal quantum efficiencies of 93% and very narrow vertical beam divergence of 7.1° (full width at half maximum). 50𝜇m broad area lasers with unpassivated facets exhibit a high total output power of nearly 20 W in pulsed mode with a divergence of 9.5°×11.3° leading to a record brightness of 3×108Wcm−2sr−1, being p...

Temperature and electric field dependence of the carrier emission processes in a quantum dot-based memory structure

Nowozin, Tobias ; Marent, A. ; Geller, Martin ; Bimberg, Dieter ; Akçay, N. ; Öncan, N. (2009-01-29)

Hole emission processes from self-organized GaAs0.4Sb0.6/GaAs quantum dots embedded in a 𝑝-𝑛 diode are studied by capacitance-voltage spectroscopy. The method introduced allows the investigation of the temperature and electric field dependence of carrier emission with time constants from below nanoseconds up to thousands of seconds. Different emission processes are clearly distinguished, such...

Role of carrier reservoirs on the slow phase recovery of quantum dot semiconductor optical amplifiers

Kim, J. ; Meuer, C. ; Bimberg, Dieter ; Eisenstein, Gadi (2009-01-28)

The gain and phase recovery dynamics of quantum-dot (QD) semiconductor optical amplifiers are calculated, including all the optical transitions involved in successive carrier recovery processes. The carrier recovery dynamics of inhomogeneously broadened QDs is simulated by solving 1088 coupled rate equations. The respective contributions of QD states and quantum-well carrier reservoirs to the g...

Frequency response of large aperture oxide-confined 850 nm vertical cavity surface emitting lasers

Mutig, A. ; Blokhin, S. A. ; Nadtochiy, A. M. ; Fiol, G. ; Lott, James A. ; Shchukin, V. A. ; Ledentsov, Nikolai N. ; Bimberg, Dieter (2009-09-28)

Small and large signal modulation measurements are carried out for 850 nm vertical cavity surface emitting lasers (VCSELs). The resonance frequency, damping factor, parasitic frequency, and 𝐷-factor are extracted. Small signal modulation bandwidths larger than 20 GHz are measured. At larger currents the frequency response becomes partially limited by the parasitics and damping. Our results ind...

BigEarthNet-MM: A Large-Scale, Multimodal, Multilabel Benchmark Archive for Remote Sensing Image Classification and Retrieval

Sumbul, Gencer ; de Wall, Arne ; Kreuziger, Tristan ; Marcelino, Filipe ; Costa, Hugo ; Benevides, Pedro ; Caetane, Mário ; Demir, Begüm ; Markl, Volker (2021-09-29)

This article presents the multimodal BigEarthNet (BigEarthNet-MM) benchmark archive consisting of 590,326 pairs of Sentinel-1 and Sentinel-2 image patches to support deep learning (DL) studies in multimodal, multilabel remote sensing (RS) image retrieval and classification. Each pair of patches in BigEarthNet-MM is annotated with multilabels provided by the CORINE Land Cover (CLC) map of 2018 b...

Hole-based memory operation in an InAs/GaAs quantum dot heterostructure

Marent, A. ; Nowozin, Tobias ; Gelze, J. ; Luckert, F. ; Bimberg, Dieter (2009-12-18)

We present an InAs/GaAs quantum dot (QD) memory structure with all-electrical data access which uses holes as charge carriers. Charging and discharging of the QDs are clearly controlled by a gate voltage. The stored information is read-out by a two-dimensional hole gas underneath the QD-layer. Time resolved drain-current-measurements demonstrate the memory operation. Present write times are 80 ns.

Hybrid mode-locking in a 40 GHz monolithic quantum dot laser

Fiol, G. ; Arsenijević, Dejan ; Bimberg, Dieter ; Vladimirov, A. G. ; Wolfrum, M. ; Viktorov, E. A. ; Mandel, Paul (2010-01-05)

Hybrid mode-locking in monolithic quantum dot (QD) lasers is studied experimentally and theoretically. A strong asymmetry of the locking range with respect to the passive mode locking frequency is observed. The width of this range increases linearly with the modulation amplitude for all operating parameters. Maximum locking range found is 30 MHz. The results of a numerical analysis performed us...

Single-photon emission from InGaAs quantum dots grown on (111) GaAs

Stock, Erik ; Warming, Till ; Ostapenko, Irina ; Rodt, Sven ; Schliwa, Andrei ; Töfflinger, Jan Amaru ; Lochmann, Anatol ; Toropov, Aleksandr I. ; Moshchenko, Sergej A. ; Dmitriev, Dimitry V. ; Haisler, Vladimir A. ; Bimberg, Dieter (2010-03-04)

In this letter, we demonstrate that self-organized InGaAs quantum dots (QDs) grown on GaAs (111) substrate using droplet epitaxy have great potential for the generation of entangled photon pairs. The QDs show spectrally sharp luminescence lines and low spatial density. A second order correlation value of g(2)(0)<0.3 proves single-photon emission. By comparing the power dependence of the lumines...

Metal-cavity surface-emitting microlaser at room temperature

Lu, Chien-Yao ; Chang, Shu-Wei ; Chuang, Shun Lien ; Germann, Tim David ; Bimberg, Dieter (2010-06-21)

We propose and realize a substrate-free metal-cavity surface-emitting microlaser with both top and sidewall metal and a bottom distributed Bragg reflector as the cavity structure. The transfer-matrix method is used to design the laser structure based on the round-trip resonance condition inside the cavity. The laser is 2.0𝜇m in diameter and 2.5𝜇m in height, and operates at room temperature wi...

Large internal dipole moment in InGaN/GaN quantum dots

Ostapenko, Irina A. ; Hönig, Gerald ; Kindel, Christian ; Rodt, Sven ; Strittmatter, André ; Hoffmann, Axel ; Bimberg, Dieter (2010-08-09)

Direct observation of large permanent dipole moments of excitonic complexes in InGaN/GaN quantum dots is reported. Characteristic traces of spectral diffusion, observed in cathodoluminescence of InGaN/GaN quantum dots, allow deducing the magnitude of the intrinsic dipole moment. Our experimental results are in good agreement with realistic calculations of quantum dot transition energies for pos...