Sommaire:

Cathodoluminescence (CL) spectroscopy in a scanning electron microscope is particularly suited for the characterisation of the local emission properties of ultra-wide bandgap materials due to the achievable spatial resolution and as there is no restriction to the bandgap energies that can be excited by the electron beam. A unique time-resolved CL system equipped has been recently installed at our institute: with rigorously UV-optimized optics and detectors, a He-cryo stage, as well as the capability for operation at low acceleration voltages achieving a particularly high spatial resolution. The combination of high spatial, spectral and temporal resolutions allows to investigate in particular the role of extended or point defects on charge carrier dynamics in widegap semiconductor layers or heterostructures, e.g. for the (Al,Ga)N material system or hBN. Therefore, such measurements can contribute to highly relevant scientific questions. For homoepitaxial AlN layers, we will show that the combination of the high spectral (1 meV) and temporal (currently 20 ps, in the future 2 ps) resolution with temperature-dependent measurements can contribute to the attribution of excitonic emission lines, the origin of which is disputed in the literature [1]. On dedicated 1-nm-thin (Al,Ga)N quantum wells covered only by a 5 nm top barrier, we can push the spatial resolution limit to reveal dark spot features with a spatial extent of only 30 nm and a density of LF^16 cm^-3, which would be consistent with an attribution to point defects. Spectrally-resolved maps indicate that these dark spots are not correlated to Al-content fluctuations. Supplemented by temperature- and time-resolved luminescence maps, we will discuss whether these features can be attributed to individual point defects acting as non-radiative centers. In analogy to studies on (In,Ga)N [2], imaging of individual point defects in quantum wells as a function of the Al content or growth parameters could notably advance the understanding of the efficiency limits of (Al,Ga)N-based UV emitters. Finally, we present first time-resolved and excitation-dependent data for the emission of excitons bound to different types of stacking faults in AlN [3]. [1] L. van Deurzen et al., APL Materials 11, 081LF9 (2023). [2] T. Weatherley et al., Nano Letters 21, 5217 (2021). [3] C. Guérin et al., J. Appl. Phys. CR7, 174303 (2025).

Pour plus d'informations, merci de contacter Cassabois G.