2019, Richter, Eberhard, Beyer, Franziska C., Zimmermann, Friederike, Gärtner, Günter, Irmscher, Klaus, Gamov, Ivan, Heitmann, Johannes, Weyers, Markus, Tränkle, Günther

Carbon-doping of GaN layers with thickness in the mm-range is performed by hydride vapor phase epitaxy. Characterization by optical and electrical measurements reveals semi-insulating behavior with a maximum of specific resistivity of 2 × 1010 Ω cm at room temperature found for a carbon concentration of 8.8 × 1018 cm−3. For higher carbon levels up to 3.5 × 1019 cm−3, a slight increase of the conductivity is observed and related to self-compensation and passivation of the acceptor. The acceptor can be identified as CN with an electrical activation energy of 0.94 eV and partial passivation by interstitial hydrogen. In addition, two differently oriented tri-carbon defects, CN-a-CGa-a-CN and CN-a-CGa-c-CN, are identified which probably compensate about two-thirds of the carbon which is incorporated in excess of 2 × 1018 cm−3. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

2013, Zeimer, U., Mogilatenko, A., Kueller, V., Knauer, A., Weyers, M.

Surface steps as high as 15 nm on up to 10 μm thick AlN layers grown on patterned AlN/sapphire templates play a major role for the structural and optical properties of AlxGa1−xN layers with x ≥ 0.5 grown subsequently by metalorganic vapour phase epitaxy. The higher the Ga content in these layers is, the stronger is the influence of the surface morphology on their properties. For x = 0.5 not only periodic inhomogeneities in the Al content due to growth of Ga-rich facets are observed by cathodoluminescence, but these facets give rise to additional dislocation formation as discovered by annular dark-field scanning transmission electron microscopy. For AlxGa1−xN layers with x = 0.8 the difference in Al content between facets and surrounding material is much smaller. Therefore, the threading dislocation density (TDD) is only defined by the TDD in the underlying epitaxially laterally overgrown (ELO) AlN layer. This way high quality Al0.8Ga0.2N with a thickness up to 1.5 μm and a TDD ≤ 5x108 cm−2 was obtained.

2012, Tränkle, G., Erbert, G., Wicht, A., Luvsandamdin, E.

[no abstract available]

2018, Radziunas, Mindaugas, Fuhrmann, Jürgen, Zeghuzi, Anissa, Wünsche, Hans-Jürgen, Koprucki, Thomas, Brée, Carsten, Wenzel, Hans, Bandelow, Uwe

In this work, we discuss the modeling of edge-emitting high-power broad-area semiconductor lasers. We demonstrate an efficient iterative coupling of a slow heat transport (HT) model defined on multiple vertical-lateral laser cross-sections with a fast dynamic electro-optical (EO) model determined on the longitudinal-lateral domain that is a projection of the device to the active region of the laser. Whereas the HT-solver calculates temperature and thermally-induced refractive index changes, the EO-solver exploits these distributions and provides time-averaged field intensities, quasi-Fermi potentials, and carrier densities. All these time-averaged distributions are used repetitively by the HT-solver for the generation of the heat sources entering the HT problem solved in the next iteration step.

2017, Kolbe, Tim, Knauer, Arne, Rass, Jens, Cho, Hyun Kyong, Hagedorn, Sylvia, Einfeldt, Sven, Kneissl, Michael, Weyers, Markus

The effects of composition and p-doping profile of the AlGaN:Mg electron blocking layer (EBL) in 310 nm ultraviolet B (UV-B) light emitting diodes (LEDs) have been investigated. The carrier injection and internal quantum efficiency of the LEDs were simulated and compared to electroluminescence measurements. The light output power depends strongly on the temporal biscyclopentadienylmagnesium (Cp 2 Mg) carrier gas flow profile during growth as well as on the aluminum profile of the AlGaN:Mg EBL. The highest emission power has been found for an EBL with the highest Cp 2 Mg carrier gas flow and a gradually decreasing aluminum content in direction to the p-side of the LED. This effect is attributed to an improved carrier injection and confinement that prevents electron leakage into the p-doped region of the LED with a simultaneously enhanced carrier injection into the active region.

2014, Hilt, O., Bahat-Treidel, E., Brunner, F., Knauer, A., Zhytnytska, R., Kotara, P., Wuerfl, J.

Normally-off high voltage GaN-HFETs for switching applications are presented. Normally-off operation with threshold voltages of 1 V and more and with 5 V gate swing has been obtained by using p-type GaN as gate. Different GaN-based buffer types using doping and backside potential barriers have been used to obtain blocking strengths up to 1000 V. The increase of the dynamic on-state resistance is analyzed for the different buffer types. The best trade-off between low dispersion and high blocking strength was obtained for a modified carbon-doped GaN-buffer that showed a 2.6x increase of the dynamic on-state resistance for 500 V switching as compared to switching from 20 V off-state drain bias. Device operation up to 200 °C ambient temperature without any threshold voltage shift is demonstrated.

2014, Hilt, Oliver

Es wurden GaN-basierte laterale Dioden mit geringer Einsatzspannung und intrinsisch selbstsperrende Transistoren für den Einsatz in Schaltkonvertern realisiert. Transisorergebnisse: - Basierend auf dem p-GaN-Gate Modul wurden selbstsperrende 100 m / 600 V Transistoren mit 1 V Einsatzspannung realisiert. - Durch den Einsatz eines eisendotierten GaN-Puffers konnte die Erhöhung des dynamischen Einschaltwiderstands für das 250 V Schalten auf den Faktor 2.6 reduziert werden. - Die Schaltverluste sind kleiner als für Si-basierte Superjunction MOSFETs. Diodenergebnisse: - Durch die Entwicklung des zurückgesetzten Anodenkontaktes konnten 300 m / 600 V Dioden mit 0.5 V Einsatzspannung realisiert werden. - Die Schaltverluste sind so klein wie bei SiC-basierten HV-Schottkydioden. - Die Dioden wurden erfolgreich im Boost-Konverter (Systemdemonstrator) der Uni Erlangen eingesetzt.

2012, Müller, André, Marschall, Sebastian, Jensen, Ole Bjarlin, Fricke, Jörg, Wenzel, Hans, Sumpf, Bernd, Andersen, Peter E.

Diode lasers are by far the most efficient lasers currently available. With the ever-continuing improvement in diode laser technology, this type of laser has become increasingly attractive for a wide range of biomedical applications. Compared to the characteristics of competing laser systems, diode lasers simultaneously offer tunability, high-power emission and compact size at fairly low cost. Therefore, diode lasers are increasingly preferred in important applications, such as photocoagulation, optical coherence tomography, diffuse optical imaging, fluorescence lifetime imaging, and terahertz imaging. This review provides an overview of the latest development of diode laser technology and systems and their use within selected biomedical applications.

2013, Mogilatenko, A., Kirmse, H., Hagedorn, S., Richter, E., Zeimer, U., Weyers, M., Tränkle, G.

a-plane (Al,Ga)N layers can be grown on patterned c-plane AlN/sapphire templates with a ridge direction along [1bar 100]Al2O3. Scanning nanobeam diffraction reveals that the formation of a-plane layers can be explained by nucleation of c-plane (Al,Ga)N with [11bar 20](Al,Ga)N

2016, Pristovsek, Markus, Han, Yisong, Zhu, Tongtong, Oehler, Fabrice, Tang, Fengzai, Oliver, Rachel A., Humphreys, Colin J., Tytko, Darius, Choi, Pyuck-Pa, Raabe, Dierk, Brunner, Frank, Weyers, Markus

We benchmarked growth, microstructure and photo luminescence (PL) of (112-2) InGaN quantum wells (QWs) against (0001) and (112-0). In incorporation, growth rate and the critical thickness of (112-2) QWs are slightly lower than (0001) QWs, while the In incorporation on (112-0) is reduced by a factor of three. A small step-bunching causes slight fluctuations of the emission wavelength. Transmission electron microscopy as well as atom probe tomography (APT) found very flat interfaces with little In segregation even for 20% In content. APT frequency distribution analysis revealed some deviation from a random InGaN alloy, but not as severe as for (112-0). The slight deviation of (112-2) QWs from an ideal random alloy did not broaden the 300 K PL, the line widths were similar for (112-2) and (0001) while (112-0) QWs were broader. Despite the high structural quality and narrow PL, the integrated PL signal at 300 K was about 4 lower on (112-2) and more than 10 lower on (112-0).