Detecting minute amounts of nitrogen in GaNAs thin films using STEM and CBED

Maryam Vatanparast; Yu-Tsun Shao; Mohana Rajpalke; Bjørn-Ove Fimland; Turid Reenaas; Randi Holmestad; Per Erik Vullum; Jian Min Zuo

doi:10.1016/j.ultramic.2021.113299

Detecting minute amounts of nitrogen in GaNAs thin films using STEM and CBED

Ultramicroscopy. 2021 Dec:231:113299. doi: 10.1016/j.ultramic.2021.113299. Epub 2021 May 7.

Authors

Maryam Vatanparast¹, Yu-Tsun Shao², Mohana Rajpalke³, Bjørn-Ove Fimland³, Turid Reenaas¹, Randi Holmestad⁴, Per Erik Vullum⁵, Jian Min Zuo⁶

Affiliations

¹ Department of Physics, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway.
² Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
³ Department of Electronic Systems, NTNU, NO-7491 Trondheim, Norway.
⁴ Department of Physics, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway. Electronic address: randi.holmestad@ntnu.no.
⁵ Department of Physics, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway; SINTEF Industry, Richard Birkelands vei 2B, NO-7491 Trondheim, Norway.
⁶ Department of Physics, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway; Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.

PMID: 34011461
DOI: 10.1016/j.ultramic.2021.113299

Abstract

Nitrogen (N) is a common element added to GaAs for band gap engineering and strain compensation. However, detection of small amounts of N is difficult for electron microscopy as well as for other chemical analysis techniques. In this work, N in GaAs is examined by using different transmission electron microscopy (TEM) techniques. While both dark-field TEM imaging using the composition sensitive (002) reflections and selected area diffraction reveal a significant difference between the doped thin-film and the GaAs substrate, spectroscopy techniques such as electron energy loss and energy dispersive X-ray spectroscopy are not able to detect N. To quantify the N content, quantitative convergent beam electron diffraction (QCBED) is used, which gives a direct evidence of N substitution and As vacancies. The measurements are enabled by the electron energy-filtered scanning CBED technique. These results demonstrate a sensitive method for composition analysis based on quantitative electron diffraction.

Keywords: Convergent beam electron diffraction (CBED); Gallium arsenide (GaAs); Scanning transmission electron microscopy (STEM).