Par Sophie Meuret
Centre d’Élaboration de Matériaux et d’Etudes Structurales - Toulouse
The development of time-resolved Cathodoluminescence (TR-CL) in a scanning electron microscope enabled the measurement of the lifetime of excited states in semiconductors with a sub-wavelength spatial resolution. It was used for example to measure the influence of stacking faults on the GaN exciton
[1], to probe the role of a silver layer on the dynamics of a YAG crystal [2] or to show the influence of stress on the optical properties of ZnO nanowires
[3]. These results demonstrate that TR-CL is essential to study the correlation between semiconductor optical and structural properties (composition, defects, strain…). While all these pioneering studies were done using a scanning electron microscope, the improvement of the spatial resolution and the combination with other electron-based spectroscopies offered by transmission electron microscopes will be a step forward for TR-CL. We recently succeed to do the first time-resolved cathodoluminescence experiments within an ultrasfast transmission electron microscope. They were performed in a unique microscope, based on a cold-FEG electron gun
[4]. This technology allows among other things to reach a spatial resolution of a few nanometres, essential for the study of III-V heterostructures. In this presentation we will discuss our latest results on InGaN quantum wells and discuss the unique features and opportunities of this technique.
______________________________________
[1] Corfdir P.
et al. Exciton localization on basal stacking faults in a-plane epitaxial lateral overgrown GaN grown by hydride vapor phase epitaxy.
J. Appl. Phys.105, 043102 (2009).
[2] Moerland RJ, Weppelman IGC, Garming MWH, Kruit P and Hoogenboom JP. Time-resolved cathodoluminescence microscopy with sub-nanosecond beam blanking for direct evaluation of the local density of states.
Opt. Express24, 24760 (2016).
[3] Fu X et al. Exciton Drift in Semiconductors under Uniform Strain Gradients: Application to Bent ZnO Microwires.
ACS Nano8, 3412–3420 (2014).
[4] Houdellier F, Caruso GM, Weber S, Kociak M and Arbouet A. Development of a high brightness ultrafast Transmission Electron Microscope based on a laser-driven cold field emission source.
Ultramicroscopy186, 128–138 (2018).
_____________________________________