Time Resolved Cathodoluminescence of InGaN/GaN Quantum Well in an Ultrafast Transmission Electron Microscope

Cathodoluminescence is the emission of visible light when an electron interacts with matter. It is a powerful technique to study the luminescence properties of semiconductors below the diffraction limit of visible light. 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 has been a step forward for TR-CL. Indeed, we recently succeed to do the first time-resolved cathodoluminescence experiments within an ultrafast transmission electron microscope [4], followed soon after by Ye-Jin Kim et al [5]. Our TRCL experiment are performed in a unique electron microscope, based on a cold-FEG electron gun [6]. This technology allows among other things to reach a spatial resolution of a few nanometers, essential for the study of III-V heterostructures.<br/>In this presentation we will discuss the advantage and inconvenient of TRCL in a UTEM and present our results on the study of charge carrier dynamics in a 4 nm In_0.3Ga_0.7N/GaN quantum well with a resolution below 10 nm. We studied the QW emission dynamic both along and across the quantum well and correlate the results with strain map and high resolution HADF images.<br/><br/><b>References</b><br/><br/>[1] P. Corfdir <i>et al.</i>, “Exciton localization on basal stacking faults in a-plane epitaxial lateral overgrown GaN grown by hydride vapor phase epitaxy,” <i>J. Appl. Phys.</i>, vol. 105, no. 4, p. 043102, 2009.<br/>[2] R. J. Moerland, I. G. C. Weppelman, M. W. H. Garming, P. Kruit, and J. P. Hoogenboom, “Time-resolved cathodoluminescence microscopy with sub-nanosecond beam blanking for direct evaluation of the local density of states,” <i>Opt. Express</i>, vol. 24, no. 21, p. 24760, 2016.<br/>[3] X. Fu <i>et al.</i>, “Exciton Drift in Semiconductors under Uniform Strain Gradients: Application to Bent ZnO Microwires,” <i>ACS Nano</i>, vol. 8, no. 4, pp. 3412–3420, 2014.<br/>[4] S. Meuret <i>et al.</i>, “Time-resolved cathodoluminescence in an ultrafast transmission electron microscope,” <i>Appl. Phys. Lett.</i>, vol. 119, no. 6, p. 6, 2021.<br/>[5] Y. J. Kim and O. H. Kwon, “Cathodoluminescence in Ultrafast Electron Microscopy,” <i>ACS Nano</i>, vol. 15, no. 12, pp. 19480–19489, 2021.<br/>[6] F. Houdellier, G. M. Caruso, S. Weber, M. Kociak, and A. Arbouet, “Development of a high brightness ultrafast Transmission Electron Microscope based on a laser-driven cold field emission source,” <i>Ultramicroscopy</i>, vol. 186, pp. 128–138, 2018.