4D-STEM for electric field mapping in semiconductor n-n junctions

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Poster Session One
Luca Reina (2), Eoin Moynihan (2), Yining Xie (2), David Cooper (1), Professor Richard Beanland (2), Professor Ana Sanchez (2)
1. Univ. Grenoble Alpes, CEA-LETI
2. University of Warwick

4D-STEM, electron microscopy, electric field mapping, p-n junctions

Abstract text

Scanning transmission electron microscopy (STEM) allows for a large suite of characterization to be performed on a material with atomic resolution precision. However, typical annular STEM detectors integrate intensity across a large range of reciprocal-space, recording a single value for each probe position and sacrificing a wealth of information [1]. The use of new fast pixelated detectors allows for a full two dimensional (2D) image of the diffraction plane to be acquired for each of these probe positions in a  2D real-space scan [2]. This provides a four dimensional (4D) dataset and the name 4D-STEM. This large dataset contains the full diffraction-space information of the transmitted beam at an atomic resolution [2]. 

As the electron beam is transmitted through a sample, it is deflected by the internal electric field. Moving the beam across a p-n junction, the convergent beam electron diffraction (CBED) pattern is shifted. This is a rigid shift for a probe size smaller than the depletion region but a more subtle redistribution of intensity for a larger probe [3]. Centre of mass (CoM) measurement of the CBED pattern intensity can be used to observe this shift and derive the electric field at the probe location [4]. This allows 4D-STEM to map the electric field across an image. By varying the convergence semi-angle of the probe, atomic scale or longer range electric fields can be mapped across different fields of view.

This study utilizes a JEOL-ARM200F in conjunction with a MerlinEM direct electron detector from Quantum Detectors to record 4D-STEM datasets. Data processing is performed using the LiberTEM [5] python package to choose the shape and dimensions of the CoM masks. This work develops a procedure to directly measure the electric field in semiconducting materials, such as p-n junctions, at varying length scales using 4D-STEM.

  1. Ophus, C. (2019). Four-Dimensional Scanning Transmission Electron Microscopy (4D-STEM): From Scanning Nanodiffraction to Ptychography and Beyond. Microscopy and Microanalysis, 25(3), 563–582. https://doi.org/10.1017/S1431927619000497
  2. Nord, M., Webster, R. W. H., Paton, K. A., McVitie, S., McGrouther, D., MacLaren, I., & Paterson, G. W. (2020). Fast Pixelated Detectors in Scanning Transmission Electron Microscopy. Part I: Data Acquisition, Live Processing, and Storage. Microscopy and Microanalysis, 26(4), 653–666. https://doi.org/10.1017/S1431927620001713
  3. Clark, L., Brown, H. G., Paganin, D. M., Morgan, M. J., Matsumoto, T., Shibata, N., Petersen, T. C., & Findlay, S. D. (2018). Probing the limits of the rigid-intensity-shift model in differential-phase-contrast scanning transmission electron microscopy. Physical Review A, 97(4), 043843. https://doi.org/10.1103/PhysRevA.97.043843
  4. Bruas, L., Boureau, V., Conlan, A. P., Martinie, S., Rouviere, J.-L., & Cooper, D. (2020). Improved measurement of electric fields by nanobeam precession electron diffraction. Journal of Applied Physics, 127(20), 205703. https://doi.org/10.1063/5.0006969
  5. Clausen, A., Weber, D., Bryan, M., Ruzaeva, K., Migunov, V., Baburajan, A., Bahuleyan, A., Caron, J., Chandra, R., Dey, S., Halder, S., Katz, D. S., Levin, B. D. A., Nord, M., Ophus, C., Peter, S., Puskás, L., Schyndel van, J., Shin, J., … Dunin-Borkowski, R. E. (2022). LiberTEM/LiberTEM: 0.10.0. https://doi.org/10.5281/ZENODO.6927963