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Behaviour of Ti/Al/Ti/Au contacts to AlGaN/GaN heterostructures at low temperature
,
Saptarsi Ghosh ,
Zhida Liang,
Chen Chen ,
Noppasorn Suphannarat,
Menno J Kappers,
David J Wallis,
Rachel A Oliver
Journal of Physics D: Applied Physics, Volume: 58, Issue: 13, Start page: 135117
Swansea University Author:
Saptarsi Ghosh
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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...
| Published in: | Journal of Physics D: Applied Physics |
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| ISSN: | 0022-3727 1361-6463 |
| Published: |
IOP Publishing
2025
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| Online Access: |
Check full text
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| URI: | https://cronfa.swan.ac.uk/Record/cronfa71578 |
| 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 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. |
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| College: |
Faculty of Science and Engineering |
| Funders: |
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. |
| Issue: |
13 |
| Start Page: |
135117 |