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Behaviour of Ti/Al/Ti/Au contacts to AlGaN/GaN heterostructures at low temperature

Francesca Adams Orcid Logo, Saptarsi Ghosh Orcid Logo, Zhida Liang, Chen Chen Orcid Logo, Noppasorn Suphannarat, Menno J Kappers, David J Wallis, Rachel A Oliver Orcid Logo

Journal of Physics D: Applied Physics, Volume: 58, Issue: 13, Start page: 135117

Swansea University Author: Saptarsi Ghosh Orcid Logo

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DOI (Published version): 10.1088/1361-6463/adafb5

Abstract

Ohmic contacts to wide bandgap nitrides have been realised, but little is known about their behaviour at low temperatures. To address this, an established Ti/Al/Ti/Au contact stack on AlGaN/GaN heterostructures has been characterised from 320 to 80 K. Two structures were investigated, with very simi...

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Published in: Journal of Physics D: Applied Physics
ISSN: 0022-3727 1361-6463
Published: IOP Publishing 2025
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URI: https://cronfa.swan.ac.uk/Record/cronfa71578
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Two structures were investigated, with very similar ambient 2D electron gas transport characteristics despite their difference in AlGaN barrier thickness and composition. This allowed for direct comparison of contact behaviour across different heterostructures. Upon annealing at &lt;800 &#xB0;C for samples with 29 nm AlGaN barriers, contacts which had Ohmic characteristics at room temperature exhibited a gradual onset of Schottky behaviour as the measurement temperature was lowered. When non-Ohmic behaviour was observed, a combination of direct tunnelling, Fowler&#x2013;Nordheim tunnelling and a thermally assisted Fowler&#x2013;Nordheim mechanism is suggested to describe the carrier transport. In this case, annealing at 800 &#xB0;C for 30 s proved sufficient to ensure Ohmic behaviour when tested from 320 to 80 K. For a heterostructure with 8 nm AlGaN, the required annealing temperature to maintain consistent Ohmic behaviour across the temperature range was reduced to 750 &#xB0;C. 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spelling 2026-04-10T14:40:57.4809836 v2 71578 2026-03-07 Behaviour of Ti/Al/Ti/Au contacts to AlGaN/GaN heterostructures at low temperature 3e247ecabd6eddd319264d066b0ce959 0000-0003-1685-6228 Saptarsi Ghosh Saptarsi Ghosh true false 2026-03-07 ACEM Ohmic contacts to wide bandgap nitrides have been realised, but little is known about their behaviour at low temperatures. To address this, an established Ti/Al/Ti/Au contact stack on AlGaN/GaN heterostructures has been characterised from 320 to 80 K. Two structures were investigated, with very similar ambient 2D electron gas transport characteristics despite their difference in AlGaN barrier thickness and composition. This allowed for direct comparison of contact behaviour across different heterostructures. Upon annealing at <800 °C for samples with 29 nm AlGaN barriers, contacts which had Ohmic characteristics at room temperature exhibited a gradual onset of Schottky behaviour as the measurement temperature was lowered. When non-Ohmic behaviour was observed, a combination of direct tunnelling, Fowler–Nordheim tunnelling and a thermally assisted Fowler–Nordheim mechanism is suggested to describe the carrier transport. In this case, annealing at 800 °C for 30 s proved sufficient to ensure Ohmic behaviour when tested from 320 to 80 K. For a heterostructure with 8 nm AlGaN, the required annealing temperature to maintain consistent Ohmic behaviour across the temperature range was reduced to 750 °C. From these observations, the determining factor for Ohmic behaviour is suggested to be the thickness of the AlGaN barrier–either as-grown, or the effective thickness following the formation of TiN protrusions into the AlGaN barrier during annealing. The understanding provided here allows tailoring of either the processing conditions or the heterostructure, and may aid with design of novel devices for low temperature operation. Journal Article Journal of Physics D: Applied Physics 58 13 135117 IOP Publishing 0022-3727 1361-6463 31 3 2025 2025-03-31 10.1088/1361-6463/adafb5 COLLEGE NANME Aerospace, Civil, Electrical, and Mechanical Engineering COLLEGE CODE ACEM Swansea University Another institution paid the OA fee This work was supported by the New Zealand Ministry of Business, Innovation and Employment (MBIE), New Zealand, Strategic Science Investment Fund ‘Advanced Energy Technology Platforms’ under contract No. RTVU2004. The EPSRC also supported this work under Grant Numbers EP/R03480X/1, EP/P00945X/1 and NS/A000054/1. 2026-04-10T14:40:57.4809836 2026-03-07T16:09:09.0078413 Faculty of Science and Engineering School of Aerospace, Civil, Electrical, General and Mechanical Engineering - Electronic and Electrical Engineering Francesca Adams 0009-0008-2033-2121 1 Saptarsi Ghosh 0000-0003-1685-6228 2 Zhida Liang 3 Chen Chen 0000-0001-9931-2650 4 Noppasorn Suphannarat 5 Menno J Kappers 6 David J Wallis 7 Rachel A Oliver 0000-0003-0029-3993 8 71578__36494__ff3ea92ee5b348c88930cbf843d3e6d9.pdf 71578.VoR.pdf 2026-04-10T14:39:49.6814506 Output 1709869 application/pdf Version of Record true ©2025 The Author(s). Released under the terms of the Creative Commons Attribution 4.0 licence. true eng https://creativecommons.org/licenses/by/4.0/
title Behaviour of Ti/Al/Ti/Au contacts to AlGaN/GaN heterostructures at low temperature
spellingShingle Behaviour of Ti/Al/Ti/Au contacts to AlGaN/GaN heterostructures at low temperature
Saptarsi Ghosh
title_short Behaviour of Ti/Al/Ti/Au contacts to AlGaN/GaN heterostructures at low temperature
title_full Behaviour of Ti/Al/Ti/Au contacts to AlGaN/GaN heterostructures at low temperature
title_fullStr Behaviour of Ti/Al/Ti/Au contacts to AlGaN/GaN heterostructures at low temperature
title_full_unstemmed Behaviour of Ti/Al/Ti/Au contacts to AlGaN/GaN heterostructures at low temperature
title_sort Behaviour of Ti/Al/Ti/Au contacts to AlGaN/GaN heterostructures at low temperature
author_id_str_mv 3e247ecabd6eddd319264d066b0ce959
author_id_fullname_str_mv 3e247ecabd6eddd319264d066b0ce959_***_Saptarsi Ghosh
author Saptarsi Ghosh
author2 Francesca Adams
Saptarsi Ghosh
Zhida Liang
Chen Chen
Noppasorn Suphannarat
Menno J Kappers
David J Wallis
Rachel A Oliver
format Journal article
container_title Journal of Physics D: Applied Physics
container_volume 58
container_issue 13
container_start_page 135117
publishDate 2025
institution Swansea University
issn 0022-3727
1361-6463
doi_str_mv 10.1088/1361-6463/adafb5
publisher IOP Publishing
college_str Faculty of Science and Engineering
hierarchytype
hierarchy_top_id facultyofscienceandengineering
hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
hierarchy_parent_title Faculty of Science and Engineering
department_str School of Aerospace, Civil, Electrical, General and Mechanical Engineering - Electronic and Electrical Engineering{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Aerospace, Civil, Electrical, General and Mechanical Engineering - Electronic and Electrical Engineering
document_store_str 1
active_str 0
description Ohmic contacts to wide bandgap nitrides have been realised, but little is known about their behaviour at low temperatures. To address this, an established Ti/Al/Ti/Au contact stack on AlGaN/GaN heterostructures has been characterised from 320 to 80 K. Two structures were investigated, with very similar ambient 2D electron gas transport characteristics despite their difference in AlGaN barrier thickness and composition. This allowed for direct comparison of contact behaviour across different heterostructures. Upon annealing at <800 °C for samples with 29 nm AlGaN barriers, contacts which had Ohmic characteristics at room temperature exhibited a gradual onset of Schottky behaviour as the measurement temperature was lowered. When non-Ohmic behaviour was observed, a combination of direct tunnelling, Fowler–Nordheim tunnelling and a thermally assisted Fowler–Nordheim mechanism is suggested to describe the carrier transport. In this case, annealing at 800 °C for 30 s proved sufficient to ensure Ohmic behaviour when tested from 320 to 80 K. For a heterostructure with 8 nm AlGaN, the required annealing temperature to maintain consistent Ohmic behaviour across the temperature range was reduced to 750 °C. From these observations, the determining factor for Ohmic behaviour is suggested to be the thickness of the AlGaN barrier–either as-grown, or the effective thickness following the formation of TiN protrusions into the AlGaN barrier during annealing. The understanding provided here allows tailoring of either the processing conditions or the heterostructure, and may aid with design of novel devices for low temperature operation.
published_date 2025-03-31T05:51:55Z
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score 11.101457

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