Applied Microscopy

  • Volume 50
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  • Pages.17.1-17.9
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  • 2020
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  • 2287-5123(pISSN)
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  • 2287-4445(eISSN)
Korean Society of Microscopy (한국현미경학회)
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Depth-dependent EBIC microscopy of radial-junction Si micropillar arrays

  • Kaden M. Powell (Electrical and Computer Engineering, University of Utah) ;
  • Heayoung P. Yoon (Electrical and Computer Engineering, University of Utah)
  • Received : 2020.07.15
  • Accepted : 2020.08.24
  • Published : 2020.12.31
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Abstract

Recent advances in fabrication have enabled radial-junction architectures for cost-effective and high-performance optoelectronic devices. Unlike a planar PN junction, a radial-junction geometry maximizes the optical interaction in the three-dimensional (3D) structures, while effectively extracting the generated carriers via the conformal PN junction. In this paper, we report characterizations of radial PN junctions that consist of p-type Si micropillars created by deep reactive-ion etching (DRIE) and an n-type layer formed by phosphorus gas diffusion. We use electron-beam induced current (EBIC) microscopy to access the 3D junction profile from the sidewall of the pillars. Our EBIC images reveal uniform PN junctions conformally constructed on the 3D pillar array. Based on Monte-Carlo simulations and EBIC modeling, we estimate local carrier separation/collection efficiency that reflects the quality of the PN junction. We find the EBIC efficiency of the pillar array increases with the incident electron beam energy, consistent with the EBIC behaviors observed in a high-quality planar PN junction. The magnitude of the EBIC efficiency of our pillar array is about 70% at 10 kV, slightly lower than that of the planar device (≈ 81%). We suggest that this reduction could be attributed to the unpassivated pillar surface and the unintended recombination centers in the pillar cores introduced during the DRIE processes. Our results support that the depth-dependent EBIC approach is ideally suitable for evaluating PN junctions formed on micro/nanostructured semiconductors with various geometry.

Keywords

Acknowledgement

The authors acknowledge the support from B. Baker, D. Magginetti, and S. Pritchett for the development of device fabrication. The radial junction processes and the EBIC data acquisition were performed at Penn State University (University Park, PA, USA) and the National Institute of Standards and Technology (Gaithersburg, MD, USA). We thank Y. Yuwen, T. Mayer, P. Haney, and N. Zhitenev for valuable discussions.

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