Experimental Nanophysics and Photonics


Our research group focuses on the growth of group III nitride nanostructures by metal organic vapor phase epitaxy (MOVPE) and their application in nanophotonic devices. The goal is to control the formation of nanostructures at the atomic scale and thus tailor the optoelectronic properties of these materials. A number of analytical methods and simulation tools are available for the structural, electrical and optical characterization of the nanostructures. A wide variety of nanophotonic devices are fabricated and characterized in the Joint Lab "GaN Optoelectronics" with the Ferdinand-Braun-Institut (FBH) and in the clean rooms of the Nanophotonics Center (NPZ). We are particularly interested in the development of UV LEDs and UV laser diodes, GaN-based surface emitting laser diodes (SCDL, VCSEL), the generation of ultrashort pulses and the realization of monomode laser diodes, as well as quantum dot-based single photon emitters (SPE).


    Epitaxie of nanostructures

    Our research focuses on the technologically relevant material system gallium nitride (GaN), aluminum nitride (AIN) and indium nitride (InN). The growth of the heterostructures, quantum films and quantum dots is performed by metal organic vapor phase epitaxy (MOVPE). A number of analytical methods are available to characterize the nanomaterials, including in-situ spectroscopic ellipsometry/reflectometry, high-resolution X-ray diffraction (HR-XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), photoluminescence spectroscopy (PL), and Hall effect measurements. In the research of new nanomaterials, we are mainly interested in the following topics:

    •  MOVPE of AlGaN and InAlGaN quantum films (QWs) for light emitters in the entire ultraviolet (UV) spectral range. Challenges are mainly new approaches to defect reduction and doping of these semiconductor materials and analysis of the structural and optical properties of the quantum films.
    • Epitaxy of InGaN heterostructures on nonpolar and semipolar GaN surfaces for laser diodes in the blue-green spectral region and long-wavelength LEDs.
    • Growth of GaN and InGaN quantum dots for single photon emitters (SPE). In this project, different approaches to the growth of GaN and InGaN quantum dot structures are investigated using MOVPE.

    Nanophotonic devices

    The nanophotonic devices group is engaged in the development of new device concepts for optoelectronics and sensor technology. We are particularly interested in the development of:

    • UV light emitting diodes (LEDs) and lasers in the far ultraviolet spectral range. The goal is to realize highly efficient UV LEDs and first laser diodes in the ultraviolet spectral range. These components are used, for example, in the purification of drinking water, in medical diagnostics (e.g. blood gas analysis) and in phototherapy. In cooperation with the Ferdinand-Braun-Institut we also realize UV LED modules, e.g. for applications in flow cytometry (Charite) and plant growth control.
    • Green laser diodes and LEDs on non-polar and semi-polar GaN substrates for applications in projection displays and biotechnology (e.g. DNA sequencing).
    • Longitudinal monomode distributed feedback (DFB) laser diodes for spectroscopy and digital holographic data storage applications.
    • Optical microcavities for single photon emitters (SPE) for applications in quantum cryptography. Surface emitting laser diodes (VCSELs) and disk lasers (SCDL) in the blue-violet spectral region. Potential applications include short-range data communications and displays.

    Fighting Germs with Far-UVC-LEDs

    Recent studies have shown that far-UVC sources (< 235 nm) can be utilized for the inactivation of multi-drug-resistant bacteria and airborne viruses without damaging the human skin. Even though the development of far-UVC-LEDs is still in its early stages, first spectrally pure 233 nm irradiation systems have already been successfully applied for the in-vivo inactivation of germs. In contrast to conventional ultraviolet sources UVC-LEDs exhibit small form factors, operate at moderate dc voltages, show long lifetimes, and the emission wavelength can be tuned to exactly match the respective application. This presentation provides an overview of the state-of-the art and prospects in the development of far-UVC-LED technologies with a focus on devices emitting around 233 nm. We will discuss the different factors that influence the external quantum efficiency (EQE) of far-UVC-LEDs, including the role of extended and point defects in AlGaN materials on the radiative recombination efficiency (RRE) and enhancing the current injection efficiency (CIE) in the AlGaN quantum well active regions. We will also discuss some of the design aspects for far-UVC irradiation systems such as the integration of bandpass filters and provide an outlook of future advances in device technology including the realization of UV micro-LEDs arrays for enhanced light extraction.
    This paper has been presented at the 1st International Congress on Far-UVC Science and Technology, Columbia University, New York City (15th June 2023).


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    ICULTA 2023

    The International Conference on UV LED Technologies & Applications - ICULTA provides a forum for the UV LED community to exchange ideas and the latest results on cutting-edge research developments.

    Heimbach Workshop XXXIV

    At the 34th International Heimbach Workshop we welcomed 32 participants from TU Berlin, TU Chemnitz, Ferdinand-Braun-Institut, Chalmers University (Gothenburg, Sweden) and Friedrich-Alexander-Universität Erlangen.