K. Tetzner¹, R. Schewski², A. Popp², S. Bin Anooz², T.-S. Chou², I. Ostermay¹, H. Kirmse³ and J. Würfl¹

Published in:

APL Mater., vol. 10, no. 7, pp. 071108, doi:10.1063/5.0094661 (2022).

Abstract:

The present work investigates the use of the refractory metal alloy TiW as a possible candidate for the realization of ohmic contacts to the ultrawide bandgap semiconductor β-Ga₂O₃. Ohmic contact properties were analyzed by transfer length measurements of TiW contacts annealed at temperatures between 400 and 900 °C. Optimum contact properties with a contact resistance down to 1.5 × 10^-5 Ω cm² were achieved after annealing at 700 °C in nitrogen on highly doped β-Ga₂O₃. However, a significant contact resistance increase was observed at annealing temperatures above 700 °C. Cross-sectional analyses of the contacts using scanning transmission electron microscopy revealed the formation of a TiO_x interfacial layer of 3-5 nm between TiW and β-Ga₂O₃. This interlayer features an amorphous structure and most probably possesses a high amount of vacancies and/or Ga impurities supporting charge carrier injection. Upon annealing at temperatures of 900 °C, the interlayer increases in thickness up to 15 nm, featuring crystalline-like properties, suggesting the formation of rutile TiO₂. Although severe morphological changes at higher annealing temperatures were also verified by atomic force microscopy, the root cause for the contact resistance increase is attributed to the structural changes in thickness and crystallinity of the interfacial layer.

Topics:

Annealing; Ohmic contacts; Atomic force microscopy; Transmission electron microscopy; Crystal structure; Epitaxy; Oxides; Semiconductor structures; Metallization process

Copyright © 2022 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/5.0094661

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