Development and implementation of trap characterisation and analysis techniques for AlGaN/GaN HEMT technology

Sampson, Wesley ORCID: https://orcid.org/0000-0001-7670-0036 2025. Development and implementation of trap characterisation and analysis techniques for AlGaN/GaN HEMT technology. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

To advance high-performance AlGaN/GaN HEMTs, understanding and mitigating trapping effects is crucial. In this research, new trap characterisation and analysis methods have been investigated and developed in order to enable detailed investigations into the impact of both fabrication processes and epi-structure variations. Initially, in collaboration with IQE, this understanding of trap characterisation and analysis was first developed, with a large variety of MIS-HEMT structures fabricated at a commercial foundry. Through the use of DC-IV characterisation, multiple trapping effects were observed and investigated, revealing novel trapping behaviour observable as an output transconductance overshoot. This enabled the development of new characterisation techniques and analysis methods enabling a greater understanding of device topology and the epi-structure on trap effects. These techniques were then applied to investigate the effect of different fabrication processes and epi-structure variations on traps. When ion implantation was compared with mesa etching for device isolation, ion implantation was found to demonstrate significant advantages over mesa etching, resulting in reduced trapping, improved drain and gate leakage, and improved overall device performance. Furthermore, AlGaN barrier thickness variations were investigated. Here, a 15 nm barrier layer was found to emerge as the optimal thickness, offering a balanced combination of high drain current density, transfer transconductance, and low leakage, while minimising trapping effects. Finally, a low Al concentration AlGaN back barrier on suppressing barrier traps was evaluated. Despite increasing self-heating, the back barrier has been shown to effectively isolate buffer traps, leading to reduced gate and drain-lag current collapse, improved DC-IV characteristics, and enhanced power added efficiency (PAE) at 8 GHz. This research provides valuable insights into trap characterisation and analysis, enabling the optimisation of AlGaN/GaN HEMT fabrication processes and epistructures for improved device performance.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Engineering
Uncontrolled Keywords:	1. AlGaN/GaN HEMT 2. Trap Characterisation 3. AlGaN/GaN Device Fabrication 4. Epitaxial Structure Optimization 5. AlGaN/GaN Device Characterisation
Funders:	EPSRC
Date of First Compliant Deposit:	19 September 2025
Last Modified:	19 Sep 2025 14:14
URI:	https://orca.cardiff.ac.uk/id/eprint/181194

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