Finch, Harry 
ORCID: 0000-0001-8470-1354
(2024)
INVESTIGATION OF METAL OXIDES ON WIDE
BAND GAP SEMICONDUCTORS FOR POWER
DEVICE APPLICATION
PhD thesis, University of Liverpool.
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Abstract
This work examines the heterojunction of various semiconductor (GaN, 4H-SiC, β-Ga2O3) and potential dielectric gate materials (Sc2O3, Y2O3, MgO) for applicatons in high power and high frequency power device applications. The primary motivation was to find suitable materials for application in the electric vehicle (EV) market; a market that has everincreasing power demands, especially as heavier vehicles - haulage and aerosapece - look to electrification. The potential gate dielectics were deposited by sputtering techniques, RF magnetron and ion beam, to create amorphous films which are expected to be better insulators compared to epitaxial films because of the lack of grain boundaries that act as low resistance conduction pathways between the transistor chanel and gate electrode. The suitability of the semiconductor/dielectric heterojuncton is assessed by determining the type of heterojunction alignment (I, II, III) via X-ray photoelectron spectroscopy (XPS): a type-I alignment with valence and conduction band offsets of more than 1 eV is desirable. Optical methods, VASE and UV-VIS, were also used to determine the band gap of the semiconductor. The band gaps and work functions of the dielectrics had to be determined from the O 1s loss and secondary electron cutoff features of the XPS features, respectively. Atomic force microscopy was also used to examine the roughness of the semiconductor surfaces. The culmination of this study is that all material combinations produce the desired type-I alignment, with the exception of the 4H-SiC/Y2O3 system which is type-II, and the conduction band offsets of all GaN systems tested are suitable confine electrons to the transistor channel while holes may not be confined in any of the GaN systems. In general, SiC systems seem to be more suitable to confining holes at the heterojunction compared with GaN. Scandia and yttria were not tested with β-Ga2O3 as their band gap could not allow the desired type I alignment, however, MgO produces a type-I alignment with a CBO and VBO values that can make it suitable for the desired power electronic applications. The novelty of this work is in the determination of the energy band alignments at heterojunctions not assessed in the literature (β-Ga2O3/MgO) or the use of sputtering techniques not previously used to create thin films as a low cost means of fabricating the amorphous films. For heterojunction system that have previously been assessed this work builds on that by providing the experimentally determined work function that are seldom reported in the band alignment literature but provide an alternative view of heterojunction band alignments and can give insights into band bending phenomenon.
| Item Type: | Thesis (PhD) |
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| Divisions: | Faculty of Science & Engineering > School of Physical Sciences |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 26 Sep 2024 10:57 |
| Last Modified: | 08 Feb 2025 03:02 |
| DOI: | 10.17638/03180550 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3180550 |
| Disclaimer: | The University of Liverpool is not responsible for content contained on other websites from links within repository metadata. Please contact us if you notice anything that appears incorrect or inappropriate. |
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