Prof. Armin Dadgar Profile

Prof. Armin Dadgar

at Otto von Guericke Univ Magdeburg

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Author

Publications (8)

Proceedings Article | 12 March 2024 Presentation

Advanced nano-characterization of an AlInN/GaN-based photonic bandgap crystal laser structure

Frank Bertram, Gordon Schmidt, Christoph Berger, Peter Veit, Jürgen Bläsing, Armin Dadgar, André Strittmatter, Juergen Christen

Proceedings Volume PC12880, PC1288005 (2024) https://doi.org/10.1117/12.3000941

KEYWORDS: Photonic crystals, Laser crystals, Crystals, Gallium nitride, Waveguides, Waveguide lasers, Superlattices, Scanning electron microscopy, Quantum wells, Quantum processes

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Proceedings Article | 4 March 2019 Presentation

Nanometer scale cathodoluminescence of GaN quantum-dots on a wavelength-matched deep-UV distributed Bragg reflector (Conference Presentation)

Hannes Schuermann, Gordon Schmidt, Christoph Berger, Sebastian Metzner, Peter Veit, Jürgen Bläsing, Frank Bertram, Armin Dadgar, André Strittmatter, Jürgen Christen, Stefan Kalinowski, Gordon Callsen, Stefan Jagsch, Markus Wagner, Axel Hoffmann

Proceedings Volume 10929, 109290A (2019) https://doi.org/10.1117/12.2510350

KEYWORDS: Vapor phase epitaxy, Gallium nitride, Deep ultraviolet, Distributed Bragg reflectors, Quantum dots, Reflectivity, Epitaxy, Single photon, Absorption, Gallium

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Proceedings Article | 14 March 2018 Presentation

Leakage currents and Fermi-level shifts in C- and Fe-doped GaN (Conference Presentation)

Aqdas Fariza, Andreas Lesnik, Silvio Neugebauer, Matthias Wieneke, Jonas Hennig, Jürgen Bläsing, Hartmut Witte, Armin Dadgar, André Strittmatter

Proceedings Volume 10532, 105320T (2018) https://doi.org/10.1117/12.2288248

KEYWORDS: Gallium nitride, Doping, Carbon, Iron, Heterojunctions, Scanning probe microscopy, Microscopy, Reflection, Surface properties, Switching

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Due to its large band gap and excellent electrical properties, nitride-based heterostructures are rapidly becoming a material of choice for RF and power switching applications. However, these devices require a carbon or iron doped semi-insulating buffer to deliver high breakdown voltages and suppress off-state leakage currents. We have grown semi-insulating GaN using precursor-based metal-organic chemical vapor phase epitaxy by intentionally introducing carbon and iron impurities with doping concentration ranging from 1x10^17cm-3 to 5x10^18cm-3 to compensate residual donors. Scanning probe microscopy techniques, scanning surface potential microscopy (SSPM) and bias dependent electric force microscopy (EFM) are mainly used to compare contact potential differences and local potential mapping at the vicinity of dislocation regions. For reference n-type GaN layers doped with Si and Ge, and p-type GaN layers doped with Mg are also investigated. Skew and edge type dislocation densities are estimated from tilt and twist x-ray diffraction measurements using omega-scans for the (0002) reflection and grazing incidence in-plane geometry for the (101 ̅0) reflection. The obtained values are in the range of low 108 cm-2 for screw-type and low 109 cm-2 for edge-type dislocations, independent of doping type and concentration. Locally probing dislocations by SSPM reveals a negative charge contrast with respect to the surrounding areas in C-doped samples increasing with doping concentration whereas Fe-doped samples exhibit no contrast. By investigating the contact potential by EFM, the combined effects of Fermi-level position and surface band bending due to surface states are determined. With the references of n-type and p-type GaN samples, the acceptor states introduced by carbon cause Fermi-level pinning below midgap position whereas acceptor-states by Fe impurities have to be energetically above midgap position. In vertical transport measurements, C-doped GaN layers with a dopant concentration of 4.6x10^18 cm-3 exhibit an up to 5 orders of magnitude lower dark current at room temperature and significantly higher thermal activations than Fe-doped samples with a comparable dopant concentration. In conclusion C-doped samples show superior properties in comparison to Fe-doped samples.

Proceedings Article | 14 March 2018 Presentation

Optical properties of doped GaN (Conference Presentation)

Axel Hoffmann, Christian Nenstiel, Markus Wagner, Felix Nippert, Gordon Callsen, Nadja Jankowski, Armin Dadgar, Stacia Keller

Proceedings Volume 10532, 105320M (2018) https://doi.org/10.1117/12.2293824

KEYWORDS: Gallium nitride, Phonons, Optical properties, Excitons, Germanium, Particles, Silicon, Silicon carbide, Carbon, Transition metals

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Proceedings Article | 14 March 2018 Presentation

Investigation of desorption-induced GaN quantum-dot formation using cathodoluminescence microscopy (Conference Presentation)

Gordon Schmidt, Hannes Schürmann, Sebastian Metzner, Peter Veit, Frank Bertram, Christoph Berger, Jürgen Bläsing, Armin Dadgar, André Strittmatter, Jürgen Christen

Proceedings Volume 10532, 105320N (2018) https://doi.org/10.1117/12.2290737

KEYWORDS: Gallium nitride, Quantum dots, Scanning electron microscopy, Electron microscopes, Metals, Vapor phase epitaxy, Scanning transmission electron microscopy, Microscopy, Ultraviolet radiation, Single photon

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Proceedings Article | 20 February 2007 Paper

Metalorganic vapor phase epitaxy of ZnO: toward p-type conductivity

S. Heinze, A. Dadgar, F. Bertram, A. Krtschil, J. Bläsing, H. Witte, S. Tiefenau, T. Hempel, A. Diez, J. Christen, A. Krost

Proceedings Volume 6474, 647406 (2007) https://doi.org/10.1117/12.715018

KEYWORDS: Zinc oxide, Arsenic, Annealing, Doping, Oxygen, Nitrogen, Zinc, Atomic force microscopy, Crystals, Particle filters

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Proceedings Article | 21 September 2006 Paper

Epitaxy of GaN LEDs on large substrates: Si or sapphire?

A. Dadgar, C. Hums, A. Diez, F. Schulze, J. Bläsing, A. Krost

Proceedings Volume 6355, 63550R (2006) https://doi.org/10.1117/12.691576

KEYWORDS: Silicon, Light emitting diodes, Sapphire, Gallium nitride, Semiconducting wafers, Patterned sapphire substrate, Indium gallium nitride, Silicon carbide, Reflection, Epitaxy

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Proceedings Article | 14 May 2001 Paper

Silicon as a substrate in multiwafer MOVPE GaN technology

Assadullah Alam, Bernd Schineller, Harry Protzmann, Markus Luenenbuerger, Michael Heuken, Michael Bremser, Egbert Woelk, Armin Dadgar, Alois Krost

Proceedings Volume 4278, (2001) https://doi.org/10.1117/12.426846

KEYWORDS: Gallium nitride, Semiconducting wafers, Silicon, Electroluminescence, Sapphire, Silicon carbide, Quantum wells, Light emitting diodes, Atomic force microscopy, Indium gallium nitride

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Showing 5 of 8 publications

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