Exploring the Dynamics of Semiconductors with an Ultrafast Transmission Electron Microscope

The development of time-resolved Cathodoluminescence (TR-CL) in a scanning electron microscope has enabled the measurement of the lifetime of excited states in semiconductors with a sub-wavelength spatial resolution [1]–[3]. For example, it was used 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 TRCL is usually done in 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 [4], [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-N heterostructures. In this presentation we will discuss for example the advantage and inconvenient of TRCL in a UTEM and present our results on the study of charge carrier dynamics in In_0.3Ga_0.7N/GaN quantum well with a resolution below 10 nm. Comparing different heterostructure we will discuss the impact of growth conditions on the optical properties (spectral and carriers dynamics). We will study the QW emission dynamic both along and across the quantum well and correlate the results with the strain maps obtained from the high resolution HAADF-STEM images[7] and temperature dependent time-resolved photoluminescence experiments<br/><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.<br/>[7] N. Cherkashin, A. Louiset, A. Chmielewski, D. J. Kim, C. Dubourdieu, and S. Schamm-Chardon, “Quantitative mapping of strain and displacement fields over HR-TEM and HR-STEM images of crystals with reference to a virtual lattice,” <i>Ultramicroscopy</i>, vol. 253, p. 113778, 2023.