4D-STEM for electric field mapping in semiconductor n-n junctions
- Abstract number
- Presentation Form
- Corresponding Email
- [email protected]
- 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 . 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 . 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 .
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 . 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 . 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  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.
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