Journal
MICROSCOPY
Volume 70, Issue 1, Pages 24-38Publisher
OXFORD UNIV PRESS
DOI: 10.1093/jmicro/dfaa061
Keywords
phase-shifting electron holography; GaAs; GaN; two-dimensional electron gas; organic semiconductor; electroluminescence
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Funding
- MEXT Project [JPMXS0410500120]
- Japan Society for the Promotion of Science (JSPS) [JP18K13795]
- Toyota Motor Corporation
- JSPS [JP19K05289, JP19K22136, JP20H02627]
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This paper introduces Phase-shifting electron holography (PS-EH) and its applications in semiconductors, demonstrating the advantages of PS-EH over conventional holography techniques and discussing the importance of observing potential distributions and electric fields.
Phase-shifting electron holography (PS-EH) is an interference transmission electron microscopy technique that accurately visualizes potential distributions in functional materials, such as semiconductors. In this paper, we briefly introduce the features of the PS-EH that overcome some of the issues facing the conventional EH based on Fourier transformation. Then, we present a high-precision PS-EH technique with multiple electron biprisms and a sample preparation technique using a cryo-focused-ion-beam, which are important techniques for the accurate phase measurement of semiconductors. We present several applications of PS-EH to demonstrate the potential in organic and inorganic semiconductors and then discuss the differences by comparing them with previous reports on the conventional EH. We show that in situ biasing PS-EH was able to observe not only electric potential distribution but also electric field and charge density at a GaAs p-n junction and clarify how local band structures, depletion layer widths and space charges changed depending on the biasing conditions. Moreover, the PS-EH clearly visualized the local potential distributions of two-dimensional electron gas layers formed at AlGaN/GaN interfaces with different Al compositions. We also report the results of our PS-EH application for organic electroluminescence multilayers and point out the significant potential changes in the layers. The proposed PS-EH enables more precise phase measurement compared to the conventional EH, and our findings introduced in this paper will contribute to the future research and development of high-performance semiconductor materials and devices.
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