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).
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:
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:
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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