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Application laboratory time-resolved cathodoluminescence spectroscopy (ZALKAL)

01/01/2023 - 31/12/2025

CL intensity map of a GaN layer showing contrast from dislocations. (top) Change of the emission energy around the position of individual dislocations. (bottom) Spectrally resolved time-trace of the CL intensity for a GaN layer. (right)

German: Applikationslabor Zeitaufgelöste Kathodolumineszenzspektroskopie (ZALKAL)

Paul Drude Institute has 30 years of experience in the field of cathodoluminescence (CL) spectroscopy, which analyzes the light emitted by semiconductors under electron irradiation. The light is emitted when charge carriers (electrons and holes) recombine and its wavelength is determined, among other things, by the band gap of the semiconductor. Based on a scanning electron microscope (SEM), this offers the possibility to investigate properties of semiconductor structures with extremely high spatial and spectral resolution. On the one hand, this allows a more detailed understanding of structural defects in the crystal structure as they influence the light emission and thus their influence on desired properties can be investigated. On the other hand, nanoscopic structures can be investigated that have been incorporated into the semiconductor to tailor its functionality. However, knowledge on the dynamics, i.e. the temporal behavior of the charge carriers, which cannot be investigated with a classical CL system, are crucial for a comprehensive understanding of where charge carriers are lost, i.e. efficiency is lost in the structures. The required high temporal resolution is achieved by pulsing the electron beam on a picosecond timescale combined with ultrafast detectors.

In 2024, PDI established an application laboratory for time-resolved cathodoluminescence spectroscopy (ZALKAL) to provide exceptional spatial, spectral, and temporal resolution. The system is equipped with optimized detectors, enabling measurements in the ultraviolet range down to approximately 180 nm, while also covering visible and near-infrared spectral regions. This broad spectral range makes it suitable for analyzing a wide variety of materials.

ZALKAL is designed to study classic semiconductor thin films and heterostructures, as well as advanced materials such as 2D systems and 3D nanostructures. The lab plays a key role in PDI’s research activities and collaborates closely with other research institutes, academic partners, and industry stakeholders in Berlin and beyond—particularly those requiring combined spectral and time-resolved luminescence mapping.

Leveraging the infrastructure of PDI’s analytical SEM lab, ZALKAL enables the correlation of cathodoluminescence data with compositional mapping (energy-dispersive X-ray spectroscopy, EDX), crystal structure analysis (electron backscatter diffraction, EBSD), and charge collection measurements (electron beam-induced current, EBIC).

The laboratory is co-funded by the European Regional Development Fund through the State of Berlin (Senate) from January 2023 to December 2025.

ZALKAL project website


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