FG Experimentelle Nanophysik und Photonik

14 Items

Recent Submissions
Novel technology and device approaches for InP-on-SOI and InP photonic integrated circuits

Keyvaninia, Shahram (2021)

Photonic integrated circuits (PICs) are key components in many areas, e.g., optical data transmission networks, sensor systems, and metrology equipment. They offer small footprint, low power consumption, and enable cost-efficient solutions. For PIC realization, monolithic InP and hybrid/heterogeneous InP on SOI are the most important technology platforms. Both have been developed in parallel an...

AlN base layers for UV LEDs

Walde, Sebastian (2021)

In this work, the aim is to improve the quality of AlN base layers on sapphire substrates to enable the fabrication of high performance ultraviolet (UV) light-emitting diodes (UV LEDs). The main issues for UV LEDs are still a limited internal quantum efficiency due to a high amount of threading dislocations, but also a limited light extraction efficiency due to total internal reflection at the ...

MOVPE growth of (In)AlGaN-based heterostructures for thin-film LEDs and VCSELs in the UVB spectral range

Enslin, Johannes-Tobias (2021)

The goal of this work is the development of efficient UVB-LEDs and VCSELs and to identify, analyze and master the challenges that arise in the process. Special attention is paid to the strain state of emitters in the UVB spectral range. The strain state is analyzed and the realization of AlGaN pseudosubstrates with high structural quality by MOVPE is discussed. Superlattice structures are used ...

Status and Prospects of AlN Templates on Sapphire for Ultraviolet Light‐Emitting Diodes

Hagedorn, Sylvia ; Walde, Sebastian ; Knauer, Arne ; Susilo, Norman ; Pacak, Daniel ; Cancellara, Leonardo ; Netzel, Carsten ; Mogilatenko, Anna ; Hartmann, Carsten ; Wernicke, Tim ; Kneissl, Michael ; Weyers, Markus (2020-03-06)

Herein, the scope is to provide an overview on the current status of AlN/sapphire templates for ultraviolet B (UVB) and ultraviolet C (UVC) light‐emitting diodes (LEDs) with focus on the work done previously. Furthermore, approaches to improve the properties of such AlN/sapphire templates by the combination of high‐temperature annealing (HTA) and patterned AlN/sapphire interfaces are discussed....

Group III-nitride based UVC LEDs and lasers with transparent AlGaN:Mg layers and tunnel junctions grown by MOVPE

Kuhn, Christian (2020)

In this work, AlGaN-based light-emitting diodes (LEDs) and lasers with emission wavelengths in the deep ultraviolet (UVC) spectral range are produced, analyzed, and optimized. Here, the focus is on the UV transparency of the structures, enabling high light extraction efficiency for UVC LEDs and being a necessary condition for UVC laser diodes, however at the same time challenging due to low ele...

Thin-film flip-chip UVB LEDs realized by electrochemical etching

Bergmann, Michael A. ; Enslin, Johannes ; Hjort, Filip ; Wernicke, Tim ; Kneissl, Michael ; Haglund, Åsa (2020-03-24)

We demonstrate a thin-film flip-chip (TFFC) light-emitting diode (LED) emitting in the ultraviolet B (UVB) at 311 nm, where substrate removal has been achieved by electrochemical etching of a sacrificial Al0.37Ga0.63N layer. The electroluminescence spectrum of the TFFC LED corresponds well to the as-grown LED structure, showing no sign of degradation of structural and optical properties by elec...

Spatial clustering of defect luminescence centers in Si-doped low resistivity Al0.82Ga0.18N

Kusch, Gunnar ; Nouf-Allehiani, M. ; Mehnke, Frank ; Kuhn, Christian ; Edwards, Paul R. ; Wernicke, Tim ; Knauer, Arne ; Kueller, Viola ; Naresh-Kumar, G. ; Weyers, Markus ; Kneissl, Michael ; Trager-Cowan, Carol ; Martin, Robert W. (2015-08-17)

A series of Si-doped AlN-rich AlGaN layers with low resistivities was characterized by a combination of nanoscale imaging techniques. Utilizing the capability of scanning electron microscopy to reliably investigate the same sample area with different techniques, it was possible to determine the effect of doping concentration, defect distribution, and morphology on the luminescence properties of...

Determination of Sapphire Off‐Cut and Its Influence on the Morphology and Local Defect Distribution in Epitaxially Laterally Overgrown AlN for Optically Pumped UVC Lasers

Enslin, Johannes ; Knauer, Arne ; Mogilatenko, Anna ; Mehnke, Frank ; Martens, Martin ; Kuhn, Christian ; Wernicke, Tim ; Weyers, Markus ; Kneissl, Michael (2019-11-12)

Herein, a systematic study of the morphology and local defect distribution in epitaxially laterally overgrown (ELO) AlN on c‐plane sapphire substrates with different off‐cut angles ranging from 0.08° to 0.23° is presented. Precise measurements of the off‐cut angle α, using a combination of optical alignment and X‐ray diffraction with an accuracy of ±5° for the off‐cut direction and ±0.015° for ...

Ultrafast optical demagnetization dynamics in thin elemental films and alloys

Willems, Felix Alexander (2019)

This thesis investigates the femtosecond photo-induced magnetization dynamics in the fundamental transition metals (TMs) Fe, Co, and Ni as well as the technologically relevant, two-component CoPt alloy. In this context, a laboratorybased higher harmonic generation (HHG) source was developed and set up which provides radiation in the extended ultraviolet (XUV) spectral range with pulse lengths o...

Prozessierung und Anwendung SiO2 basierter Lichtleiter für die optische UVC-Gassensorik

Elmlinger, Philipp Simon (2019)

Diese Arbeit behandelt die Prozessierung verlustarmer Lichtwellenleiter für einen optischen UVC-Gassensor. Durch optische Simulationen wurde zunächst ein geeignetes Material (amorphes Quarzglas) und Design abgeleitet. Mittels Belichtung mit einem Ultrakurzpulslaser und anschließendem selektiven Nassätzen wurden die Lichtleiter aus dem Wafer strukturiert. Die resultierenden rauen Seitenwände füh...

A Miniaturized UV-LED Based Optical Gas Sensor Utilizing Silica Waveguides for the Measurement of Nitrogen Dioxide and Sulphur Dioxide

Elmlinger, Philipp ; Schreivogel, Martin ; Weida, Simon ; Kneissl, Michael (2017-08-15)

Continuing advances in the development of light-emitting diodes (LEDs) in the deep ultraviolet spectral range (DUV) enable miniaturized, mobile, and cost-effective DUV gas sensors. Efficient light coupling, guiding, and splitting plays a key role for stable sensor systems and is realized by lowloss silica based waveguides, fabricated by ultrashort pulsed laser etching and laser polishing. The t...

Effect of Electron Blocking Layer Doping and Composition on the Performance of 310 nm Light Emitting Diodes

Kolbe, Tim ; Knauer, Arne ; Rass, Jens ; Cho, Hyun ; Hagedorn, Sylvia ; Einfeldt, Sven ; Kneissl, Michael ; Weyers, Markus (2017-12-06)

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...

Optical gain and modal loss in AlGaN based deep UV lasers

Martens, Martin Georg Rudolf (2018)

Because of its direct bandgap covering the ultraviolet (UV) spectral region from 360 nm to 200 nm, the AlGaN material system is a promising candidate for the realization of deep UV laser diodes emitting below 300 nm, being an alternative for bulky and energy consuming excimer or frequency multiplied lasers. Possible applications cover e.g. medical detection, gas sensing, material processing, ...

The fate of the 2√3 × 2√3R(30°) silicene phase on Ag(111)

Liu, Zhi-Long ; Wang, Mei-Xiao ; Liu, Canhua ; Jia, Jin-Feng ; Vogt, Patrick ; Quaresima, Claudio ; Ottaviani, Carlo ; Olivieri, Bruno ; Padova, Paola de ; Lay, Guy Le (2014)

Silicon atoms deposited on Ag(111) produce various single layer silicene sheets with different buckling patterns and periodicities. Low temperature scanning tunneling microscopy reveals that one of the silicene sheets, the hypothetical √7 × √7 silicene structure, on 2√3 × 2√3 Ag(111), is inherently highly defective and displays no long-range order. Moreover, Auger and photoelectron spectroscopy...