44 results on '"Carsten Netzel"'
Search Results
2. Role of Oxygen Incorporation in High Temperature Annealed AlGaN
- Author
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Norzaini Zainal, Sylvia Hagedorn, Carsten Netzel, Anna Mogilatenko, Matthias Schön, and Markus Weyers
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Materials Chemistry ,Surfaces and Interfaces ,Electrical and Electronic Engineering ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Published
- 2023
3. Optimization of the Epitaxial Growth of Undoped GaN Waveguides in GaN-Based Laser Diodes Evaluated by Photoluminescence
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Markus Weyers, Carsten Netzel, Sven Einfeldt, and Veit Hoffmann
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Photoluminescence ,Materials science ,Gallium nitride ,02 engineering and technology ,01 natural sciences ,chemistry.chemical_compound ,charge carrier diffusion ,0103 physical sciences ,Materials Chemistry ,Electrical and Electronic Engineering ,Triethylgallium ,Trimethylgallium ,Konferenzschrift ,Quantum well ,010302 applied physics ,Phonon scattering ,business.industry ,Doping ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,chemistry ,Optoelectronics ,photoluminescence ,Charge carrier ,0210 nano-technology ,business ,MOVPE growth - Abstract
Non-intentionally doped c-plane GaN layers are generally employed as p-side waveguide layers in violet/blue-emitting laser diodes. The recombination and diffusion of charge carriers in the p-side GaN waveguide influence the injection efficiency of holes into the InGaN quantum wells of these devices. In this study, the non-radiative recombination and the diffusivity in the [000-1] direction for charge carriers in such GaN layers are investigated by the photoluminescence of buried InGaN quantum wells, in addition to the GaN photoluminescence. The vertical charge carrier diffusion length and the diffusion constant in GaN were determined by evaluating the intensity from InGaN quantum wells in different depths below a top GaN layer. Additionally, the intensity from the buried InGaN quantum wells was found to be more sensitive to variations in the non-radiative recombination rate in the GaN layer than the intensity from the GaN itself. The study enables conclusions to be drawn on how the growth of a p-side GaN waveguide layer has to be optimized: (1) The charge carrier diffusivity in the [000-1] direction at device operation temperature is limited by phonon scattering and can be only slightly improved by material quality. (2) The use of TMGa (trimethylgallium) instead of TEGa (triethylgallium) as a precursor for the growth of GaN lowers the background silicon doping level and is advantageous for a large hole diffusion length. (3) Small growth rates below 0.5 μm/h when using TMGa or below 0.12 μm/h when using TEGa enhance non-radiative recombination. (4) A V/III gas ratio of 2200 or more is needed for low non-radiative recombination rates in GaN.
- Published
- 2020
4. Advances towards deep-UV light emitting diode technologies
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Sebastian Walde, Johannes Enslin, Tim Wernicke, Michael Kneissl, Luca Sulmoni, Hyun Kyong Cho, Norman Susilo, Martin Guttmann, Johannes Glaab, Neysha Lobo-Ploch, Giulia Cardinali, Carsten Netzel, Markus Weyers, Jan Ruschel, Marcel Schilling, Christian Kuhn, S. Hagedorn, Jens Rass, U. Winterwerber, Frank Mehnke, and Sven Einfeldt
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Materials science ,business.industry ,Wide-bandgap semiconductor ,Optical polarization ,medicine.disease_cause ,law.invention ,law ,medicine ,Optoelectronics ,Quantum efficiency ,Light emission ,Metalorganic vapour phase epitaxy ,business ,Quantum well ,Ultraviolet ,Light-emitting diode - Abstract
Driven by a wide range of applications, as shown in Fig. 1(a) , the development of AlGaN-based light emitting diodes in the deep ultraviolet spectral range (DUV-LEDs) has greatly intensified. In contrast to conventional ultraviolet sources UV-LEDs exhibit small form factors, operate at moderate dc voltages, show long lifetimes, and their emission covers the entire UVB and large parts of the UVC wavelength range. Currently, the main driving force are high volume applications like water purification, disinfection of surfaces and appliances, inactivation of germs in air treatment systems as well as sterilization of medical equipment with a focus on UVC-LEDs emitting near the germicidal effectiveness peak around 270 nm [1] . This presentation will provide an overview of state-of-the art in DUV-LED device technologies and present recent advances in the development of high quality AlGaN materials by metalorganic vapour phase epitaxy (MOVPE). We will discuss different approaches to improve the internal quantum efficiency of UV light emitters, including the growth of low defect density AlN layers on sapphire substrates by epitaxial lateral overgrowth (ELO) as well as sputtered and high temperature annealed AlN on sapphire [2] . We will demonstrate AlGaN quantum well (QW) LEDs with output powers of more than 50 mW for single-chip emitters near 265 nm and explore the wavelength limits of deep UV-LEDs with emission as short as 217 nm. These far UV-LEDs are ideally suited for sensing applications like the monitoring of combustion engines, toxic gases, nitrates in water, and may also be utilized for the in-vivo inactivation of multi-drug-resistant germs or viruses without damaging the human skin. Although a strong decline can be observed in the external quantum efficiency (EQE) of UV-LEDs emitting below 250 nm, as shown in Fig 1(b) , considerable advances have been made in the development of 233 nm LEDs with output powers of nearly 1.9 mW at 100 mA corresponding to an EQE of 0.35% [4] . We will discuss the root causes for the EQE decline, including changes in the optical polarization of light emission from deep UV AlGaN QWs and their effects on light extraction as well as changes in internal quantum efficiency and carrier confinement. We will provide an outlook of future progress in DUV-LED performance and demonstrate first applications including a spectrally pure 233 nm irradiation system for the in-vivo inactivation of germs.
- Published
- 2021
5. Crystal defect analysis in AlN layers grown by MOVPE on bulk AlN
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Markus Weyers, Andrea Dittmar, Uta Juda, Carsten Netzel, Jürgen Wollweber, Carsten Hartmann, Arne Knauer, Anna Mogilatenko, Jörg Jeschke, Ralph-Stephan Unger, Matthias Bickermann, and Ute Zeimer
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010302 applied physics ,Materials science ,business.industry ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Inorganic Chemistry ,Crystal ,0103 physical sciences ,Materials Chemistry ,Optoelectronics ,Metalorganic vapour phase epitaxy ,Dislocation ,0210 nano-technology ,business - Abstract
MOVPE growth of AlN layers on bulk AlN substrates with low threading dislocation density (
- Published
- 2019
6. AlGaN-based deep UV LEDs: applications and challenges
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Christian Kuhn, Neyhsa Lobo-Ploch, Frank Mehnke, Sven Einfeldt, Norman Susilo, Markus Weyers, Giulia Cardinali, Jan Ruschel, Tim Wernicke, Sylvia Hagedorn, Luca Sulmoni, Jens Rass, Johannes Enslin, Hyun Kyong Cho, Johannes Glaab, Martin Guttmann, Michael Kneissl, and Carsten Netzel
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Materials science ,Wavelength range ,business.industry ,Heterojunction ,Combustion ,medicine.disease_cause ,Toxic gas ,law.invention ,law ,Sapphire ,medicine ,Optoelectronics ,business ,Ultraviolet ,Light-emitting diode - Abstract
Driven by applications like monitoring of combustion engines, toxic gases, nitrates in water, as well as the inactivation of multi-drug-resistant germs, the development of AlGaN-based light emitting diodes in the deep ultraviolet spectral range (DUV-LEDs) has markedly intensified. This paper will provide a review of recent advances in development of DUV-LEDs, including the realization of low defect density AlGaN heterostructures on sapphire substrates. The performance characteristics of DUV LEDs emitting in the wavelength range between 260 nm and 217 nm will be discussed and milli-Watt power LEDs near 233 nm will be demonstrated.
- Published
- 2021
7. Temperature Dependence of Dark Spot Diameters in GaN and AlGaN
- Author
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Frank Brunner, Markus Weyers, Anna Mogilatenko, Arne Knauer, and Carsten Netzel
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Threading dislocations ,Materials science ,business.industry ,cathodoluminescence ,Cathodoluminescence ,Dark spot ,threading dislocations ,Condensed Matter Physics ,dark spots ,Electronic, Optical and Magnetic Materials ,AlGaN ,internal quantum efficiency ,Optoelectronics ,Quantum efficiency ,business - Abstract
Threading dislocations in c-plane (Al,Ga)N layers are surrounded by areas with reduced light generation efficiency, called “dark spots.” These areas are observable in luminescence measurements with spatial resolution in the submicrometer range. Dark spots reduce the internal quantum efficiency in single layers and light-emitting devices. In cathodoluminescence measurements, the diameter of dark spots (full width at half maximum [FWHM]) is observed to be 200–250 nm for GaN. It decreases by 30–60% for AlxGa1−xN with x ≈ 0.5. Furthermore, the dark spot diameter increases with increasing temperature from 83 to 300 K in AlGaN, whereas it decreases in GaN. Emission energy mappings around dark spots become less smooth and show sharper features on submicrometer scales at low temperature for AlGaN and, on the contrary, at high temperature for GaN. It is concluded that charge carrier localization dominates the temperature dependence of dark spot diameters and of the emission energy distribution around threading dislocations in AlGaN, whereas the temperature-dependent excitation volume in cathodoluminescence and charge carrier diffusion limited by phonon scattering are the dominant effects in GaN. Consequently, with increasing temperature, nonradiative recombination related to threading dislocations extends to wider regions in AlGaN, whereas it becomes spatially limited in GaN.
- Published
- 2021
8. High‐Temperature Annealing of AlGaN
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Sylvia Hagedorn, Carsten Hartmann, Taimoor Khan, Carsten Netzel, Sebastian Walde, and Markus Weyers
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Materials science ,business.industry ,Annealing (metallurgy) ,Ultraviolet light emitting diodes ,Materials Chemistry ,Optoelectronics ,Surfaces and Interfaces ,Electrical and Electronic Engineering ,Condensed Matter Physics ,business ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Published
- 2020
9. Overcoming the excessive compressive strain in AlGaN epitaxy by introducing high Si-doping in AlN templates
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Sebastian Walde, Chia-Lung Tsai, Hsueh Hsing Liu, Carsten Netzel, Markus Weyers, Sylvia Hagedorn, Yuh-Renn Wu, Yi Keng Fu, and Chia-Yen Huang
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Materials science ,Physics and Astronomy (miscellaneous) ,Strain (chemistry) ,business.industry ,Doping ,General Engineering ,General Physics and Astronomy ,Epitaxy ,law.invention ,Template ,law ,Optoelectronics ,Dislocation ,business ,Light-emitting diode - Published
- 2020
10. Temperature‐Dependent Charge Carrier Diffusion in [0001¯] Direction of GaN Determined by Luminescence Evaluation of Buried InGaN Quantum Wells
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Sven Einfeldt, Jens W. Tomm, Markus Weyers, Carsten Netzel, Veit Hoffmann, and Felix Mahler
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chemistry.chemical_compound ,Materials science ,chemistry ,Condensed matter physics ,Gallium nitride ,Charge carrier ,Diffusion (business) ,Condensed Matter Physics ,Luminescence ,Quantum well ,Electronic, Optical and Magnetic Materials - Published
- 2020
11. Improved performance of UVC-LEDs by combination of high-temperature annealing and epitaxially laterally overgrown AlN/sapphire
- Author
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Sylvia Hagedorn, Tim Wernicke, Jens Rass, Michael Kneissl, Eviathar Ziffer, Martin Guttmann, Shaojun Wu, Markus Weyers, Norman Susilo, Martin Albrecht, Leonardo Cancellara, Neysha Lobo Ploch, Sebastian Walde, Luca Sulmoni, and Carsten Netzel
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Materials science ,business.industry ,Aluminium nitride ,Annealing (metallurgy) ,Cathodoluminescence ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,010309 optics ,chemistry.chemical_compound ,chemistry ,law ,0103 physical sciences ,Sapphire ,Optoelectronics ,Quantum efficiency ,0210 nano-technology ,business ,Light-emitting diode ,Diode - Abstract
We report on the performance of AlGaN-based deep ultraviolet light-emitting diodes (UV-LEDs) emitting at 265 nm grown on stripe-patterned high-temperature annealed (HTA) epitaxially laterally overgrown (ELO) aluminium nitride (AlN)/sapphire templates. For this purpose, the structural and electro-optical properties of ultraviolet-c light-emitting diodes (UVC-LEDs) on as-grown and on HTA planar AlN/sapphire as well as ELO AlN/sapphire with and without HTA are investigated and compared. Cathodoluminescence measurements reveal dark spot densities of 3.5 × 10 9 cm − 2 , 1.1 × 10 9 cm − 2 , 1.4 × 10 9 cm − 2 , and 0.9 × 10 9 cm − 2 in multiple quantum well samples on as-grown planar AlN/sapphire, HTA planar AlN/sapphire, ELO AlN/sapphire, and HTA ELO AlN/sapphire, respectively, and are consistent with the threading dislocation densities determined by transmission electron microscopy (TEM) and high-resolution X-ray diffraction rocking curve. The UVC-LED performance improves with the reduction of the threading dislocation densities (TDDs). The output powers (measured on-wafer in cw operation at 20 mA) of the UV-LEDs emitting at 265 nm were 0.03 mW (planar AlN/sapphire), 0.8 mW (planar HTA AlN/sapphire), 0.9 mW (ELO AlN/sapphire), and 1.1 mW (HTA ELO AlN/sapphire), respectively. Furthermore, Monte Carlo ray-tracing simulations showed a 15% increase in light-extraction efficiency due to the voids formed in the ELO process. These results demonstrate that HTA ELO AlN/sapphire templates provide a viable approach to increase the efficiency of UV-LEDs, improving both the internal quantum efficiency and the light-extraction efficiency.
- Published
- 2020
12. Status and Prospects of AlN Templates on Sapphire for Ultraviolet Light‐Emitting Diodes
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Sylvia Hagedorn, Tim Wernicke, Anna Mogilatenko, Arne Knauer, Markus Weyers, Sebastian Walde, Daniel Pacak, Michael Kneissl, Leonardo Cancellara, Carsten Netzel, Carsten Hartmann, and Norman Susilo
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Materials science ,Template ,business.industry ,Ultraviolet light emitting diodes ,Materials Chemistry ,Sapphire ,Optoelectronics ,Surfaces and Interfaces ,Electrical and Electronic Engineering ,Condensed Matter Physics ,business ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Published
- 2020
13. AlN overgrowth of nano-pillar-patterned sapphire with different offcut angle by metalorganic vapor phase epitaxy
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Sebastian Walde, Tim Wernicke, Norman Susilo, Eviathar Ziffer, Markus Weyers, L. Matiwe, T. Straubinger, Pierre-Marie Coulon, Carsten Hartmann, Carol Trager-Cowan, Jonas Weinrich, Philip A. Shields, Anna Mogilatenko, A. Alasmari, Carsten Netzel, Gunnar Kusch, Robert W. Martin, Sylvia Hagedorn, Michael Kneissl, M. Bickermann, and G. Naresh-Kumar
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Materials science ,Scanning electron microscope ,02 engineering and technology ,Epitaxy ,01 natural sciences ,law.invention ,Inorganic Chemistry ,law ,0103 physical sciences ,Nano ,Materials Chemistry ,Lithography ,QC ,010302 applied physics ,business.industry ,technology, industry, and agriculture ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Sapphire ,Optoelectronics ,sense organs ,Dry etching ,Inductively coupled plasma ,0210 nano-technology ,business ,Light-emitting diode - Abstract
We present overgrowth of nano-patterned sapphire with different offcut angles by metalorganic vapor phase epitaxy. Hexagonal arrays of nano-pillars were prepared via Displacement Talbot Lithography and dry-etching. 6.6 µm crack-free and fully coalesced AlN was grown on such substrates. Extended defect analysis comparing X-ray diffraction, electron channeling contrast imaging and selective defect etching revealed a threading dislocation density of about 109 cm-2. However, for c-plane sapphire offcut of 0.2° towards m direction the AlN surface shows step bunches with a height of 10 nm. The detrimental impact of these step bunches on subsequently grown AlGaN multi-quantum-wells is investigated by cathodoluminescence and transmission electron microscopy. By reducing the sapphire offcut to 0.1° the formation of step bunches is successfully suppressed. On top of such a sample an AlGaN-based UVC LED heterostructure is realized emitting at 265 nm and showing an emission power of 0.81 mW at 20 mA (corresponds to an external quantum efficiency of 0.86 %).
- Published
- 2020
14. Improving AlN Crystal Quality and Strain Management on Nanopatterned Sapphire Substrates by High‐Temperature Annealing for UVC Light‐Emitting Diodes
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Michael Kneissl, Sebastian Walde, Christiane Becker, Carsten Netzel, Sylvia Hagedorn, Eviathar Ziffer, Nadine Tillner, Norman Susilo, Ralph-Stephan Unger, Hans-Jürgen Lugauer, Phillip Manley, Markus Weyers, and Tim Wernicke
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010302 applied physics ,Materials science ,Annealing (metallurgy) ,business.industry ,Ultraviolet light emitting diodes ,02 engineering and technology ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,law ,0103 physical sciences ,Materials Chemistry ,Sapphire ,Optoelectronics ,Electrical and Electronic Engineering ,0210 nano-technology ,business ,Light-emitting diode - Abstract
BMBF, 03ZZ0134B, Zwanzig20 - Advanced UV for Life - Verbundvorhaben: UV Power; TP2: Entwicklung von high-power UVB-LEDs um 300 nm
- Published
- 2020
15. UV-C Lasing From AlGaN Multiple Quantum Wells on Different Types of AlN/Sapphire Templates
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Markus Weyers, Joerg Jeschke, Tim Wernicke, Martin Martens, V. Kueller, Arne Knauer, Michael Kneissl, Christian Kuhn, Christoph Reich, Ute Zeimer, Felix Krueger, and Carsten Netzel
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Materials science ,Photoluminescence ,business.industry ,Wide-bandgap semiconductor ,Physics::Optics ,Epitaxy ,Laser ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,Optical pumping ,Condensed Matter::Materials Science ,law ,Sapphire ,Optoelectronics ,Electrical and Electronic Engineering ,Dislocation ,business ,Lasing threshold - Abstract
AlGaN multiple quantum well lasers for optical pumping have been grown by metal-organic vapor phase epitaxy on high and low dislocation density AlN/sapphire templates. Lasers on planar templates exhibited high dislocation densities and high V-pit densities, but a smooth surface morphology leading to inefficient, but laterally very homogeneous optical emission. Lasing was not observed when optically pumped with up to 50 MW/cm2. Epitaxially laterally overgrown templates on patterned sapphire showed much lower dislocation densities, but also step bunching on the surface. This resulted in good photoluminescence efficiencies of up to 20%, but also in a higher lateral inhomogeneity of the emission. Lasers on these templates exhibited lasing at $\sim 240$ nm with low full-width at half-maximum of 1 nm and threshold power densities of 11–15 MW/cm2.
- Published
- 2015
16. Influence of barrier growth schemes on the structural properties and thresholds of InGaN quantum well laser diodes
- Author
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Michael Kneissl, Ute Zeimer, Veit Hoffmann, Sven Einfeldt, Carsten Netzel, Markus Weyers, and Anna Mogilatenko
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Materials science ,Photoluminescence ,Laser diode ,business.industry ,Heterojunction ,Cathodoluminescence ,Condensed Matter Physics ,Laser ,law.invention ,Inorganic Chemistry ,Optical pumping ,law ,Materials Chemistry ,Optoelectronics ,Quantum well laser ,business ,Quantum well - Abstract
The influence of the (In)GaN quantum barrier growth temperature on the structural properties of the active region of blue–violet laser diodes has been investigated. Therefore, multiple quantum well structures were prepared by metal-organic vapor phase epitaxy, with (In)GaN barriers grown either at the same temperature as the InGaN quantum wells, or at a 60 K higher growth temperature. A 60 K higher growth temperature results in smoother quantum barrier layers with fewer defects on a microscopic scale, as revealed by scanning electron microscopy and cathodoluminescence studies. On the other hand samples with a 0 K offset showed a higher strain in the quantum wells determined by X-ray diffraction and a narrower photoluminescence emission spectra. Secondly, laser heterostructures with InGaN barriers were prepared for optical pumping using different growth schemes. The laser structure with the active region deposited with a 0 K offset exhibits significantly lower optical threshold power densities of around 200 kW/cm² compared to 700 kW/cm² for the 60 K offset sample. Also, transmission electron microscopy revealed quantum wells with improved lateral uniformity in the samples grown without temperature offset. Based on these results, a current-injection broad area laser diode with an active region growth scheme without temperature offset was prepared on (0001) GaN substrate. The diode emits around 420 nm with a threshold current density of around 1.6 kA/cm².
- Published
- 2014
17. Performance Characteristics of UV-C AlGaN-Based Lasers Grown on Sapphire and Bulk AlN Substrates
- Author
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Christian Kuhn, Markus Weyers, Carsten Hartmann, Chirstoph Reich, Tim Wernicke, A. Knauer, Juergen Wollweber, Carsten Netzel, Martin Martens, Jens Rass, Matthias Bickermann, Frank Mehnke, Michael Kneissl, and V. Kueller
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Materials science ,business.industry ,Physics::Optics ,Heterojunction ,Substrate (electronics) ,Epitaxy ,Laser ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,Optical pumping ,Condensed Matter::Materials Science ,law ,Sapphire ,Optoelectronics ,Electrical and Electronic Engineering ,Dislocation ,business ,Lasing threshold - Abstract
The performance characteristics of optically pumped laser heterostructures emitting in the UV-C spectral range between 272 and 279 nm are investigated. The laser heterostructures were grown by metal-organic vapor phase epitaxy on (0001) planar AlN/sapphire, epitaxially laterally overgrown (ELO) AlN/sapphire, and bulk AlN substrates with threading dislocation densities ranging from 2×1010 to 104 cm-2. We found that the defect density strongly affects the laser performance. The lowest pulse threshold energy density of 50 mJ/cm2 under resonant optical pumping condition was obtained for an AlGaN multiple quantum well laser grown pseudomorphically on low defect density bulk AlN substrate. Lasing was also observed for AlGaN MQW heterostructures grown on ELO AlN/sapphire templates. The laser emission in all lasers was TE polarized. However, no lasing was observed for heterostructures grown on high defect density AlN/sapphire.
- Published
- 2014
18. Time-resolved photoluminescence from n-doped GaN/Al0.18Ga0.82N short-period superlattices probes carrier kinetics and long-term structural stability
- Author
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Carsten Netzel, Veit Hoffmann, Jens W. Tomm, Felix Mahler, Thomas Elsaesser, Markus Weyers, Michael Woerner, and Klaus Reimann
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010302 applied physics ,Photoluminescence ,Materials science ,Superlattice ,Kinetics ,Doping ,Relaxation (NMR) ,Time constant ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,Condensed Matter::Materials Science ,0103 physical sciences ,Exponential decay ,0210 nano-technology ,Excitation - Abstract
Heavily n-doped GaN/Al0.18Ga0.82N short-period superlattices with and without SiN protection layers are studied in spectrally and temporally resolved photoluminescence (PL) experiments. The room-temperature PL from a protected sample displays a nonexponential decay with an initial decay time of 150 ps for low excitation levels and an exponential decay with a time constant of ∼300 ps for higher excitation. The PL decays are governed by nonradiative carrier relaxation into deep defect states which are partially saturated at high excitation densities. PL measurements at low sample temperature reveal a marked influence of carrier cooling on the PL kinetics in a time range up to 50 ps and a significant radiative decay component. SiN coatings are shown to provide long-term stabilization of surface morphology while increasing nonradiative carrier relaxation rates.
- Published
- 2019
19. High power UVB light emitting diodes with optimized n-AlGaN contact layers
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Arne Knauer, Jan Ruschel, Tim Kolbe, Sylvia Hagedorn, Johannes Glaab, Carsten Netzel, Neysha Lobo-Ploch, Sven Einfeldt, Jens Rass, Markus Weyers, and Hyun Kyong Cho
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010302 applied physics ,Emission power ,Materials science ,Photoluminescence ,Physics and Astronomy (miscellaneous) ,business.industry ,General Engineering ,General Physics and Astronomy ,Conductivity ,01 natural sciences ,Crystallographic defect ,Power (physics) ,law.invention ,law ,Electrical resistivity and conductivity ,0103 physical sciences ,Optoelectronics ,business ,Voltage ,Light-emitting diode - Abstract
The influence of the n-AlGaN contact layer thickness and doping profile on the efficiency, operating voltage and lifetime of 310 nm LEDs has been investigated. Increasing the n-contact layer thickness reduces the operation voltage of the LEDs and increases the emission power slightly. Optimizing the n-doping profile yielded enhanced conductivity and reduced operation voltage with a simultaneous output power enhancement of the LEDs. Lifetime measurements have shown that even though the output power of the LEDs was enhanced the lifetimes were not negatively affected. Room temperature photoluminescence indicates a low concentration of point defects in the n-doping region yielding minimum AlGaN resistivity.
- Published
- 2019
20. Influence of silicon doping on internal quantum efficiency and threshold of optically pumped deep UV AlGaN quantum well lasers
- Author
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Ute Zeimer, Anna Mogilatenko, Carsten Netzel, Markus Weyers, and Joerg Jeschke
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Materials science ,Silicon ,business.industry ,Doping ,chemistry.chemical_element ,Condensed Matter Physics ,medicine.disease_cause ,Laser ,Electronic, Optical and Magnetic Materials ,law.invention ,chemistry ,law ,Materials Chemistry ,medicine ,Optoelectronics ,Quantum efficiency ,Electrical and Electronic Engineering ,business ,Quantum well ,Ultraviolet - Published
- 2018
21. MOVPE growth of Al0.85Ga0.15As for high power laser diodes emitting at 808nm
- Author
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Frank Bugge, Markus Weyers, and Carsten Netzel
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Materials science ,business.industry ,Slope efficiency ,Condensed Matter Physics ,Cladding (fiber optics) ,Laser ,Reflectivity ,law.invention ,Inorganic Chemistry ,law ,Materials Chemistry ,Optoelectronics ,Metalorganic vapour phase epitaxy ,business ,Diode - Abstract
Al 0.85 Ga 0.15 As cladding layers in 808 nm laser diodes grown by MOVPE result in inferior device performance when grown with the same growth parameters as the standard Al 0.7 Ga 0.3 As cladding layers. Using in-situ reflectance the interface between lower n-Al 0.85 Ga 0.15 As cladding and n-Al 0.45 Ga 0.55 As waveguide is found as the origin of deterioration due to 3-D growth of the cladding. The growth mode of Al 0.85 Ga 0.15 As was studied under different conditions, and the growth process was optimized to sustain 2-D growth throughout the structure. This way laser diodes with low divergence, a high slope efficiency and a high characteristic temperature are realized.
- Published
- 2013
22. Si Doping of GaN in Hydride Vapor-Phase Epitaxy
- Author
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Markus Weyers, Günther Tränkle, Toma Stoica, Eberhard Richter, Carsten Netzel, and Ute Zeimer
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Fabrication ,Materials science ,Solid-state physics ,Hydride ,business.industry ,Doping ,Dichlorosilane ,Condensed Matter Physics ,Epitaxy ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,chemistry ,Materials Chemistry ,Sapphire ,Optoelectronics ,Electrical and Electronic Engineering ,Dislocation ,business - Abstract
Growth of GaN boules by hydride vapor-phase epitaxy (HVPE) is very attractive for fabrication of GaN substrates. Use of dichlorosilane as a source for Si doping of bulk GaN is investigated. It is shown that no tensile strain is incorporated into mm-thick, Si-doped GaN layers on sapphire substrates if the threading dislocation density is previously reduced to 2.5 × 107 cm−2 or below. High-quality GaN layers with electron densities up to 1.5 × 1019 cm−3 have been achieved, and an upper limit of about 4 × 1019 cm−3 for Si doping of GaN boules was deduced considering the evolution of dislocations with thickness. A 2-inch, Si-doped GaN crystal with length exceeding 6 mm and targeted Si doping of about 1 × 1018 cm−3 is demonstrated.
- Published
- 2012
23. Growth of GaN boules via vertical HVPE
- Author
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M. Gründer, Günther Tränkle, Eberhard Richter, Carsten Netzel, and Markus Weyers
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Photoluminescence ,Materials science ,Boule ,Plane (geometry) ,business.industry ,Exciton ,Condensed Matter Physics ,Inorganic Chemistry ,Cracking ,Material quality ,Materials Chemistry ,Sapphire ,Optoelectronics ,business ,Line (formation) - Abstract
GaN boules were grown up to thicknesses of 6.3 mm via vertical HVPE on 2 in. GaN/sapphire templates. The usable boule length is limited by surface defects. Two different sub-surface disturbances were identified to be responsible for these surface defects using optical inspection and low-temperature photoluminescence on polished m -plane slices cut from the boules. One disturbance starts already at the interface to the used template resulting in large V-pits at the surface. The other one occurs after undisturbed GaN growth of several mm and leads to local cracking networks and small V-pits at the surface. Both lead to deteriorated structural properties of subsequently grown material with red-shifted and broadened exciton emission. In contrast, the undisturbed material having a smooth surface is of high material quality and shows constant energies of the exciton emissions with narrow line widths.
- Published
- 2012
24. GaN boules grown by high rate HVPE
- Author
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Frank Brunner, B. Schineller, Markus Weyers, M. Gründer, Günther Tränkle, Ute Zeimer, Eberhard Richter, and Carsten Netzel
- Subjects
Fabrication ,Materials science ,Silicon ,business.industry ,chemistry.chemical_element ,Substrate (electronics) ,Condensed Matter Physics ,Thermal conductivity ,chemistry ,Impurity ,Optoelectronics ,Metalorganic vapour phase epitaxy ,Dislocation ,Luminescence ,business - Abstract
The most promising approach for GaN substrate fabrication on the base of HVPE consists in the growth of thick GaN crystals and subsequent cutting of these boules into slices followed by conventional surface preparation. This work focusses on a HVPE GaN boule growth process optimized to highest growth rate and the use of a commercially available vertical HVPE reactor from AIXTRON in order to develop a technology of high productivity to enable low-cost substrates. To this end, GaN crystals up to thicknesses of 6.3 mm have been grown on 2 inch GaN-on-sapphire templates produced by MOVPE. The rate in HVPE growth was 450 µm/h and the material properties of the crystals have been evaluated. No degradation of the material quality was found by comparison of structural, optical and transport properties with published data of the state of the art of bulk GaN. Dislocation densities as low as 6x105 cm-2, high electron mobility of 960 cm2/Vs for a carrier density of 1x1016 cm-3, low background impurity incorporation of oxygen and silicon, luminescence with well resolved excitonic emission, and a high value of thermal conductivity of 294±44 W/mK were determined. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
- Published
- 2011
25. Well width study of InGaN multiple quantum wells for blue–green emitter
- Author
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Arne Knauer, Ute Zeimer, Jürgen Christen, Günther Tränkle, Michael Kneissl, Veit Hoffmann, Marcus Weyers, Carsten Netzel, Frank Bertram, and Sven Einfeldt
- Subjects
Condensed Matter::Quantum Gases ,Diffraction ,Indium nitride ,Materials science ,Condensed Matter::Other ,business.industry ,Quantum point contact ,technology, industry, and agriculture ,chemistry.chemical_element ,Cathodoluminescence ,equipment and supplies ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Epitaxy ,Inorganic Chemistry ,stomatognathic diseases ,chemistry.chemical_compound ,Wavelength ,Optics ,chemistry ,Materials Chemistry ,Optoelectronics ,business ,Indium ,Quantum well - Abstract
InGaN/GaN multiple quantum well structures emitting in the blue/green wavelength region were grown by metal organic vapor phase epitaxy. By reducing the quantum well growth time the influence of the quantum well thicknesses between 3.8 and 1.1 nm on the indium incorporation and the distribution of indium in the quantum wells in growth direction were investigated. X-ray diffraction measurements show that the average indium mole fraction in the quantum wells decreases with reducing quantum well width due to a delay in the indium incorporation at the barrier/well interface. Quantitative analysis reveals a segregation length of about 2 nm as a measure of the graded region in growth direction. Cathodoluminescence imaging reveals that the spatial variation of the wavelength is reduced with decreasing quantum well thickness down to 1.7 nm. Reducing the width of the quantum well further results in an increase of the spatial wavelength variation.
- Published
- 2010
26. Influence of MOVPE growth temperature on the structural and optical properties of InGaN MQW laser diodes
- Author
-
Arne Knauer, Ute Zeimer, Sven Einfeldt, Carsten Netzel, Karolis Kazlauskas, Günther Tränkle, Saulius Jursenas, U. Jahn, Michael Kneissl, Veit Hoffmann, J.M. Karaliunas, Markus Weyers, J.-R. van Look, and Frank Brunner
- Subjects
Indium nitride ,Materials science ,business.industry ,Gallium nitride ,Condensed Matter Physics ,Laser ,Semiconductor laser theory ,law.invention ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,law ,Materials Chemistry ,Optoelectronics ,Metalorganic vapour phase epitaxy ,Trimethylindium ,business ,Lasing threshold ,Quantum well - Abstract
The morphological and optical properties of InGaN multiple quantum wells (MQWs) emitting at 405 nm are studied with respect to the MQW growth temperature. The latter was varied between 760 and 840 °C in structures grown on c -plane sapphire substrates by metal-organic vapor-phase epitaxy (MOVPE). The indium content in the quantum well was kept constant for all temperatures by adjusting the trimethylindium supply. The MQWs were inserted as active region in both optically pumped laser heterostructures and laser diodes (LDs). We found that low growth temperatures result in a reduced spatial uniformity of the luminescence emission wavelength due to well thickness variations, whereas at higher temperatures it is difficult to obtain a spatially homogeneous indium concentration. A minimum threshold power density for optically pumped lasing was found for growth temperatures of the active region between 780 and 820 °C. LDs with an MQW grown at these conditions showed an onset of lasing at a current density of 6.5 kA/cm 2 with output powers of more than 350 mW.
- Published
- 2008
27. Near band edge and defect emissions from epitaxial lateral overgrown a-plane GaN with different stripe orientations
- Author
-
Tim Wernicke, Ute Zeimer, Michael Kneissl, Frank Brunner, Carsten Netzel, and Markus Weyers
- Subjects
Photoluminescence ,Materials science ,Plane (geometry) ,business.industry ,Cathodoluminescence ,Gallium nitride ,Condensed Matter Physics ,Epitaxy ,Molecular physics ,Inorganic Chemistry ,chemistry.chemical_compound ,Optics ,chemistry ,Materials Chemistry ,Sapphire ,Dislocation ,business ,Non-radiative recombination - Abstract
Epitaxial lateral overgrowth (ELOG) of a -plane GaN on r -plane sapphire with stripe orientations parallel to [0 0 0 1], [ 0 1 1 1 ], and [ 0 1 1 0 ] has been investigated. The emission from ELOG stripes with different orientations and from different growth facets has been compared by spectrally and spatially resolved cathodoluminescence and by temperature-dependent photoluminescence measurements. A reduction in the nonradiative recombination rate by the ELOG process is clearly observed. For all stripe orientations the ELOG wing regions exhibit increased radiative emission intensities compared to the window areas, indicating a reduced dislocation density in the overgrown areas. The highest increase of the near band edge (NBE) emission is observed in the wing regions for stripes parallel to [ 0 1 1 0 ]. In this region, the density of basal plane stacking faults (BSFs) is also reduced. NBE emission is detected up to temperatures of 250 K.
- Published
- 2008
28. Avoidance of instable photoluminescence intensity from AlGaN bulk layers
- Author
-
Jörg Jeschke, Markus Weyers, Carsten Netzel, and Arne Knauer
- Subjects
010302 applied physics ,Photoluminescence ,Materials science ,business.industry ,Band gap ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Emission intensity ,Electronic, Optical and Magnetic Materials ,Semiconductor ,0103 physical sciences ,Optoelectronics ,Photoluminescence excitation ,Charge carrier ,0210 nano-technology ,business ,Intensity (heat transfer) ,Surface states - Abstract
The emission intensity from c-plane AlGaN bulk layers changes strongly on time scales from seconds to hours during above band gap illumination in photoluminescence experiments. Responsible for this effect is the accumulation of photo-generated charge carriers at the semiconductor surface, modifying surface states and surface recombination. The effect has a negative impact on the exactness and comparability of photoluminescence intensity measurements, especially for measurements with long exposure times or repeated excitation on the same spot. We realized temporally stable photoluminescence intensity by using an AlN cap layer separating the studied AlGaN bulk layer from the crystal surface. We verified the temporal stability in temperature-dependent photoluminescence measurements in vacuum and in ambient air. Surface recombination was suppressed for the capped AlGaN layer, resulting in significantly higher emission intensity at room temperature.
- Published
- 2017
29. Comparative study of buffer designs for high breakdown voltage AlGaNGaN HFETs
- Author
-
Melanie Cho, Carsten Netzel, Eldad Bahat-Treidel, Frank Brunner, Joachim Würfl, Oliver Hilt, and Markus Weyers
- Subjects
Materials science ,business.industry ,Transistor ,Analytical chemistry ,Trapping ,Double heterostructure ,Condensed Matter Physics ,Buffer (optical fiber) ,law.invention ,law ,Breakdown voltage ,Optoelectronics ,Drain current ,business ,Leakage (electronics) ,Voltage - Abstract
A comparison of different epilayer concepts to achieve high breakdown voltage AlGaN-GaN HFETs is presented. A double heterostructure with a low Al-content Al0.05Ga0.95N back-barrier as well as a carbon-doped GaN buffer are investigated with regard to material and device properties. Material analysis reaffirms the incorporation of carbon on a nitrogen lattice site without creation of extended defects or causing memory effects. It is demonstrated that carrier trapping in the buffer using carbon deep acceptors reduces sub-threshold drain leakage currents in HFET devices enabling breakdown voltages above 1 kV. An undoped GaN channel layer is shown to suppress drain current reduction under pulsed transistor operation. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
- Published
- 2011
30. Study of excess carrier dynamics in polar, semi‐polar, and non‐polar (In,Ga)N epilayers and QWs
- Author
-
Tim Wernicke, Ramūnas Aleksiejūnas, Mikas Vengris, L. Lubys, Michael Kneissl, Kęstutis Jarašiūnas, Veit Hoffmann, Arne Knauer, Markus Weyers, and Carsten Netzel
- Subjects
Photoluminescence ,Materials science ,business.industry ,Trapping ,Orders of magnitude (numbers) ,Grating ,Condensed Matter Physics ,Molecular physics ,Sapphire ,Polar ,Optoelectronics ,Diffusion (business) ,business ,Quantum well - Abstract
We studied carrier recombination and diffusion in GaN/sapphire templates, (In,Ga)N layers, and (In,Ga)N quantum well structures oriented along the polar [0001], semi-polar [11-22], and non-polar [11-20] orientations by means of light induced transient grating, differential transmission, and photoluminescence optical techniques. We show that the lifetime of excess carriers drops by orders of magnitude when changing the orientation from polar to non-polar, both in GaN templates and (In,Ga)N layers. We attribute the shorter lifetime to carrier trapping by extended structural defects that are more abundant in non-polar grown samples. In addition, we observe pronounced carrier localization effects in the semi- and non-polar layers. We show that thick (In,Ga)N layers inherit the properties of the GaN templates. However, the thin quantum well structures show a lower carrier trapping activity. So, a better electrical quality can be assumed as compared to the thick (In,Ga)N layers. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
- Published
- 2011
31. GaInN quantum well design and measurement conditions affecting the emission energy S‐shape
- Author
-
Markus Weyers, Michael Kneissl, Veit Hoffmann, Tim Wernicke, Carsten Netzel, Soheil Hatami, and Arne Knauer
- Subjects
Physics ,Condensed Matter::Materials Science ,Photoluminescence ,Condensed matter physics ,Quantum efficiency ,Spontaneous emission ,Charge carrier ,Emission spectrum ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Piezoelectricity ,Excitation ,Quantum well - Abstract
Polarization fields and charge carrier localization are the dominant factors defining the radiative recombination processes in the quantum wells of most AlGaInN-based optoelectronic devices. Both factors determine emission energy, emission line width, recombination times, and internal quantum efficiency. For a deeper understanding of the charge carrier recombination processes, we have performed temperature and excitation power dependent photoluminescence experiments on epitaxially grown GaInN structures to study the S-shape of the temperature dependent emission energy. The S-shape behaviour in GaInN quantum wells (QWs) is dominated by the temperature dependence of the charge carrier localization. However, in polar QWs it is strongly affected by the charge carrier density which screens the piezoelectric field. External applied fields change the observable S-shape characteristic significantly. Semi- and nonpolar GaInN QWs feature an S-shape behaviour which points to much stronger charge carrier localization compared to polar QWs. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
- Published
- 2011
32. Band gap renormalization and Burstein-Moss effect in silicon- and germanium-doped wurtzite GaN up to1020 cm−3
- Author
-
Hartmut Witte, Alois Krost, Karsten Lange, Sarah Osterburg, Christian Lidig, Jürgen Bläsing, Bernd Garke, Armin Dadgar, Eberhard Richter, Martin Feneberg, Carsten Netzel, S. Fritze, Norbert Esser, Rüdiger Goldhahn, and Maciej D. Neumann
- Subjects
Physics ,Electron density ,Condensed matter physics ,Band gap ,Exciton ,Doping ,Condensed Matter Physics ,Energy (signal processing) ,Electronic, Optical and Magnetic Materials ,Wurtzite crystal structure ,Burstein–Moss effect ,Mott transition - Abstract
The interplay between band gap renormalization and band filling (Burstein-Moss effect) in n-type wurtzite GaN is investigated. For a wide range of electron concentrations up to $1.6\ifmmode\times\else\texttimes\fi{}{10}^{20}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ spectroscopic ellipsometry and photoluminescence were used to determine the dependence of the band gap energy and the Fermi edge on electron density. The band gap renormalization is the dominating effect up to an electron density of about $9\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$; at higher values the Burstein-Moss effect is stronger. Exciton screening, the Mott transition, and formation of Mahan excitons are discussed. A quantitative understanding of the near gap transition energies on electron density is obtained. Higher energy features in the dielectric functions up to $10\phantom{\rule{4pt}{0ex}}\mathrm{eV}$ are not influenced by band gap renormalization.
- Published
- 2014
33. Effects of low charge carrier wave function overlap on internal quantum efficiency in GaInN quantum wells
- Author
-
Michael Kneissl, Veit Hoffmann, Carsten Netzel, Arne Knauer, Tim Wernicke, and Markus Weyers
- Subjects
Physics ,Photoluminescence ,Condensed matter physics ,Condensed Matter::Other ,Quantum point contact ,Quantum-confined Stark effect ,Charge carrier ,Quantum efficiency ,Spontaneous emission ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Wave function ,Quantum well - Abstract
To determine relevant processes affecting the internal quantum efficiency in GaInN quantum well structures, we have studied the temperature and excitation power dependent photoluminescence intensity for quantum wells with different well widths on (0001) c-plane GaN and for quantum wells on nonpolar (11-20) a-plane GaN. In thick polar quantum wells, the quantum confined Stark effect (QCSE) causes a stronger intensity decrease with increasing temperature as long as the radiative recombination dominates. At higher temperatures, when the nonradiative recombination becomes more important, thick polar quantum wells feature a lower relative intensity decrease than thinner polar or nonpolar quantum wells. Excitation power dependent photoluminescence points to a transition from a recombination of excitons to a bimolecular recombination of uncorrelated charge carriers for thick polar quantum wells in the same temperature range. This transition might contribute to the limitation of nonradiative recombination by a reduced diffusivity of charge carriers. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
- Published
- 2010
34. Semipolar GaN grown on m‐plane sapphire using MOVPE
- Author
-
Tim Wernicke, Michael Kneissl, Carsten Netzel, and Markus Weyers
- Subjects
Materials science ,business.industry ,Stacking ,Gallium nitride ,Condensed Matter Physics ,chemistry.chemical_compound ,chemistry ,Sapphire ,Optoelectronics ,Crystallite ,Metalorganic vapour phase epitaxy ,Specular reflection ,business ,Layer (electronics) ,Stacking fault - Abstract
We have investigated the MOVPE growth of semipolar gallium nitride (GaN) films on (100) m-plane sapphire substrates. Specular GaN films with a RMS roughness (10 × 10 μm2) of 15.2 nm were obtained and an arrowhead like structure aligned along [113] is prevailing. The orientation relationship was determined by XRD and yielded (22)GaN ‖ (100)sapphire and [113]GaN ‖ [0001]sapphire as well as [113]GaN ‖ [000]sapphire. PL spectra exhibited near band edge emission accompanied by a strong basal plane stacking fault emission. In addition lower energy peaks attributed to prismatic plane stacking faults and donor acceptor pair emission appeared in the spectrum. With similar growth conditions also (10) GaN films on m-plane sapphire were obtained. In the later case we found that the layer was twinned, crystallites with different c-axis orientation were present. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
- Published
- 2008
35. Temperature and doping dependent changes in surface recombination during UV illumination of (Al)GaN bulk layers
- Author
-
Frank Brunner, Jörg Jeschke, Carsten Netzel, Arne Knauer, and Markus Weyers
- Subjects
010302 applied physics ,Photoluminescence ,Materials science ,Band gap ,business.industry ,Doping ,Wide-bandgap semiconductor ,General Physics and Astronomy ,02 engineering and technology ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,Condensed Matter::Materials Science ,Semiconductor ,0103 physical sciences ,Optoelectronics ,0210 nano-technology ,business ,Power density ,Surface states - Abstract
We have studied the effect of continuous illumination with above band gap energy on the emission intensity of polar (Al)GaN bulk layers during the photoluminescence experiments. A temporal change in emission intensity on time scales from seconds to hours is based on the modification of the semiconductor surface states and the surface recombination by the incident light. The temporal behavior of the photoluminescence intensity varies with the parameters such as ambient atmosphere, pretreatment of the surface, doping density, threading dislocation density, excitation power density, and sample temperature. By means of temperature-dependent photoluminescence measurements, we observed that at least two different processes at the semiconductor surface affect the non-radiative surface recombination during illumination. The first process leads to an irreversible decrease in photoluminescence intensity and is dominant around room temperature, and the second process leads to a delayed increase in intensity and beco...
- Published
- 2016
36. Effect of ridge waveguide etch depth on laser threshold of InGaN MQW laser diodes
- Author
-
Martin Martens, Michael Kneissl, A. Linke, Luca Redaelli, Sven Einfeldt, Hans Wenzel, Joachim Piprek, Günther Tränkle, Yu. V. Flores, and Carsten Netzel
- Subjects
Materials science ,business.industry ,Single-mode optical fiber ,Physics::Optics ,Indium gallium nitride ,Laser ,law.invention ,Semiconductor laser theory ,chemistry.chemical_compound ,Resonator ,Optics ,chemistry ,law ,Optoelectronics ,business ,Lasing threshold ,Waveguide ,Diode - Abstract
The laser threshold and lateral mode confinement of blue (440 nm) InGaN multiple quantum well (MQW) laser diodes have been investigated. Ridge-waveguide (RW) laser diodes with different ridge etch depth ranging from 25 nm above the active region (deep-ridge waveguide) to 200 nm above the active region (shallow-ridge waveguide) have been fabricated. The comparison of devices with the same resonator length shows that the threshold current densities are significantly lower for deep-ridge waveguide laser diodes. The difference in lasing threshold becomes more eminent for narrow ridges, which are required for single mode operation. For shallow-ridge devices the threshold current density increases by more than a factor of three when the ridge width is decreased from 20μm to 1.5μm. For the deep-ridge waveguide devices instead, the lasing threshold is almost independent of the ridge waveguide width. The effect has been analyzed by 2D self-consistent electro-optical simulations. For deep-ridge devices, the simulated thresholds and far-field patterns are in good agreement with the simulations. For shallow-ridge devices, however, questionable theoretical assumptions are needed. Two possible causes are discussed: extremely large current spreading and strong index anti-guiding.
- Published
- 2012
37. Experimental method for scanning the surface depletion region in nitride based heterostructures
- Author
-
Markus Weyers, Hans Wenzel, Jaroslava Skriniarova, Martin Herms, Arne Knauer, Carsten Netzel, and Veit Hoffmann
- Subjects
Semiconductor ,Condensed matter physics ,Depletion region ,Field (physics) ,Chemistry ,business.industry ,Electric field ,Heterojunction ,Emission spectrum ,Electronic structure ,Condensed Matter Physics ,business ,Quantum well - Abstract
The group-III-nitride semiconductors feature strong spontaneous polarization in the [0001] direction and charges on the respective polar surfaces. Within the resulting surface depletion region the surface field causes band banding and affects the optical transitions in quantum wells. We studied the changes of the emission characteristics of a single GaInN quantum well when its distance to the surface and the influence of the surface field varies. We observe a strong increase of the quantum well emission energy and a decrease of the line width when the surface field partially compensates the piezoelectric field of the quantum well. A scan of the total surface depletion region with a single quantum well as probe was performed. The obtained emission data allow for the direct determination of the width of the depletion region. The experimental method is promising for studies of the surface field and the surface potential of III-nitride surfaces and interfaces. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
- Published
- 2009
38. HVPE growth of Al x Ga 1–x N alloy layers
- Author
-
Sylvia Hagedorn, Markus Weyers, Eberhard Richter, Günther Tränkle, Carsten Netzel, and Ute Zeimer
- Subjects
Diffraction ,Chemistry ,Band gap ,Alloy ,Hydride vapour phase epitaxy ,Analytical chemistry ,engineering ,Cathodoluminescence ,Crystallite ,engineering.material ,Condensed Matter Physics ,Luminescence ,Mole fraction - Abstract
In this work growth of AlxGa1–xN layers (0 < x < 0.91) by hydride vapour phase epitaxy (HVPE) is presented. The growth process is performed in a modified horizontal reactor. The measured compositions show good agreement with theoretical values calculated from a heterogeneous thermodynamic equilibrium model. The aluminum mole fractions, the homogeneity and the relaxation of the AlxGa1–xN layers are deduced from x-ray diffraction (XRD) measurements. Cathodoluminescence (CL) investigations of an Al0.52Ga0.48N sample exhibit a luminescence peak energy near the expected band edge and an additional luminescence peak between the AlxGa1–xN and the GaN bandgap. From XRD and spatially resolved CL measurements the peak at lower energy can be associated to crystallites with orientation different from the c-plane bulk layer that are formed on the growing surface. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
- Published
- 2009
39. Polarization of photoluminescence emission from semi-polar (11–22) AlGaN layers
- Author
-
Michael Winkler, Rüdiger Goldhahn, Martin Frentrup, Frank Mehnke, Carsten Netzel, Martin Feneberg, Michael Kneissl, Markus Weyers, Joachim Stellmach, and Tim Wernicke
- Subjects
Photoluminescence ,Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,Wide-bandgap semiconductor ,Optical polarization ,Polarization (waves) ,Molecular physics ,Electric field ,Sapphire ,Optoelectronics ,business ,Luminescence ,Stacking fault - Abstract
We studied the optical polarization of surface-emitted photoluminescence from thick semi-polar (11–22) AlxGa1−xN layers on m-plane sapphire substrates with aluminum contents x between 0.0 and 0.63 at T = 10 K. Luminescence with an electric field vector E parallel to the in-plane direction [1–100] prevails for x 0.2. In case of low aluminum content, the spectra are dominated by basal plane stacking fault emission. The degree of optical polarization for both basal plane stacking fault emission and near band edge emission is comparable.
- Published
- 2014
40. Quantum Efficiency Analysis of Near-Ultraviolet Emitting AlGaN and AlInGaN Structures
- Author
-
Arne Knauer, Carsten Netzel, and Markus Weyers
- Subjects
Range (particle radiation) ,Materials science ,Photoluminescence ,Band gap ,business.industry ,General Engineering ,General Physics and Astronomy ,chemistry.chemical_element ,chemistry ,Aluminium ,Optoelectronics ,Quantum efficiency ,Charge carrier ,Near ultraviolet ,business ,Indium - Abstract
The quantum efficiency of c-plane Al x Ga1-x N and Al x In y Ga1-x-y N structures (x = 0.06–0.21, y = 0.015–0.05) emitting in the UV spectral range between 320 and 350 nm was analyzed using temperature-dependent and polarization-resolved photoluminescence measurements. We found increasing bandgap fluctuation and charge carrier localization in case of higher aluminum or higher indium content. Improved suppression of nonradiative recombination was observed only in case of indium incorporation. The light polarization changed from E⊥c to E∥c with increasing aluminum content in AlGaN. It switched back to E⊥c by the incorporation of indium in AlInGaN. Light polarization significantly contributes to the photoluminescence intensity measured from the top, and the degree of light polarization decreases with increasing temperature. Thus, temperature-dependent photoluminescence measured via the c-plane surface was found to depend both on internal quantum efficiency and on extraction efficiency.
- Published
- 2013
41. Impact of light polarization on photoluminescence intensity and quantum efficiency in AlGaN and AlInGaN layers
- Author
-
Carsten Netzel, Markus Weyers, and A. Knauer
- Subjects
Photoluminescence ,Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,Wide-bandgap semiconductor ,chemistry.chemical_element ,Polarization (waves) ,Emission intensity ,chemistry ,Aluminium ,Optoelectronics ,Quantum efficiency ,business ,Indium - Abstract
We analyzed emission intensity, quantum efficiency, and emitted light polarization of c-plane AlGaN and AlInGaN layers (λ = 320–350 nm) by temperature dependent photoluminescence. Low indium content in AlInGaN structures causes a significant intensity increase by change of the polarization of the emitted light. Polarization changes from E ⊥ c to E ‖ c with increasing aluminum content. It switches back to E ⊥ c with the incorporation of indium. The polarization degree decreases with temperature. This temperature dependence can corrupt internal quantum efficiency determination by temperature dependent photoluminescence.
- Published
- 2012
42. Indium incorporation and emission wavelength of polar, nonpolar and semipolar InGaN quantum wells
- Author
-
Ulrich T. Schwarz, Markus Weyers, Tim Wernicke, Simon Ploch, Arne Knauer, Michael Kneissl, Carsten Netzel, Veit Hoffmann, Lukas Schade, and Jens Rass
- Subjects
Photoluminescence ,Condensed matter physics ,Chemistry ,chemistry.chemical_element ,Electroluminescence ,Condensed Matter Physics ,Epitaxy ,Molecular physics ,Electronic, Optical and Magnetic Materials ,Crystal ,symbols.namesake ,Stark effect ,Materials Chemistry ,symbols ,Electrical and Electronic Engineering ,Luminescence ,Quantum well ,Indium - Abstract
InGaN quantum wells were grown by metal organic vapor-phase epitaxy on polar (0 0 0 1), nonpolar (1 0 0) and on semipolar (1 0 2), (1 1 2), (1 0 1) as well as (2 0 1) oriented GaN substrates. The room-temperature photoluminescence (PL) and electroluminescence (EL) emission energies for quantum wells grown on different crystal orientations show large variations of up to 600 meV. The following order of the emission energy was found throughout the entire range of growth temperatures: (1 0 1) < (1 1 2) = (0 0 0 1) < (2 0 1) < (1 0 0) = (1 0 2). In order to differentiate between the effects of strain, quantum-confined stark effect (QCSE) and indium incorporation the experimental data were compared to k.p theory-based calculations for differently oriented InGaN QWs. The major contribution to the shift between (1 0 0) and (0 0 0 1) InGaN quantum wells can be attributed to the QCSE. The redshift between (1 0 0) and the semipolar (1 0 2) and (2 0 1) QWs can be attributed to shear and anisotropic strain affecting the valence band structure. Finally, for (1 1 2) and (1 0 1) the emission energy shift could be attributed to a significantly higher indium incorporation efficiency.
- Published
- 2012
43. Strong charge carrier localization interacting with extensive nonradiative recombination in heteroepitaxially grown m-plane GaInN quantum wells
- Author
-
Andrei Vescan, Michael Heuken, Holger Kalisch, Tim Wernicke, Markus Weyers, C. Mauder, B. Reuters, Michael Kneissl, and Carsten Netzel
- Subjects
Physics ,Photoluminescence ,Condensed matter physics ,Band gap ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Semiconductor laser theory ,Condensed Matter::Materials Science ,Electro-absorption modulator ,Materials Chemistry ,Quantum efficiency ,Charge carrier ,Spontaneous emission ,Electrical and Electronic Engineering ,Quantum well - Abstract
The development of GaInN quantum well structures with nonpolar crystal orientation for light-emitting diodes and semiconductor lasers is currently one of the main foci of III-nitride-based optoelectronics research. One of the advantages of nonpolar orientations is the absence of polarization fields perpendicular to the quantum well plane. As a consequence, radiative recombination rates are higher compared to quantum wells on polar surfaces. However, due to high densities of threading dislocations and basal plane stacking faults in the case of heteroepitaxially grown nonpolar layers, and due to band gap inhomogeneities in the GaInN quantum wells, characterization of radiative and nonradiative recombination mechanisms is a complex challenge. So far, most published data about band gap fluctuations, charge carrier localization and internal quantum efficiency in nonpolar quantum wells are ambiguous. Here, we present temperature and excitation power density-dependent photoluminescence data featuring multiple characteristics related to strong charge carrier localization in m-plane (1–100) GaInN quantum wells. Thermally activated redistribution of charge carriers between localization sites in these quantum wells is weaker than in polar c-plane ones. The localization strength increases with higher indium concentration in the quantum wells. In the heteroepitaxially grown quantum well structures, the internal quantum efficiency is reduced even at low temperatures (T = 10 K) and especially for m-plane quantum wells with high indium mole fractions.
- Published
- 2011
44. Temperature and excitation power dependent photoluminescence intensity of GaInN quantum wells with varying charge carrier wave function overlap
- Author
-
Michael Kneissl, Veit Hoffmann, N. Szabo, Carsten Netzel, Tim Wernicke, Markus Weyers, and A. Knauer
- Subjects
Photoluminescence ,Condensed matter physics ,Condensed Matter::Other ,Chemistry ,Quantum point contact ,Quantum-confined Stark effect ,General Physics and Astronomy ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Molecular physics ,Condensed Matter::Materials Science ,Electro-absorption modulator ,Spontaneous emission ,Quantum efficiency ,Wave function ,Quantum well - Abstract
For the realization and the improvement of GaN-based optoelectronic devices (light emitting diodes and laser diodes) emitting from the ultraviolet to the red wavelength range GaInN quantum well structures with high internal quantum efficiency are of great importance. To determine parameters which affect the internal quantum efficiency, we have analyzed the emission intensity of GaInN quantum well structures with varied electron and hole wave function overlap by temperature and excitation power dependent and by time-resolved photoluminescence. The quantum confined Stark effect reduces the temperature dependent photoluminescence emission intensity for thick polar quantum wells at low temperature. But near room temperature, these thick polar GaInN quantum wells feature less relative intensity loss than thinner polar quantum wells. This behavior can partially be assigned to increased screening effects and higher quantum well barriers for thicker quantum wells. Additionally, excitation power dependent photoluminescence points to a transition from a radiative recombination based on excitons at 10 K to a bimolecular recombination at room temperature for thick c-plane quantum wells. This transition may also affect the intensity decrease by a changed carrier diffusivity.
- Published
- 2010
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