Smith, Niamh;
(2025)
Investigating p-doping related impurities within 4H-SiC to improve device channel mobility.
Masters thesis (M.Phil), UCL (University College London).
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Abstract
Inversion channel field-effect mobilities of 4H-SiC MOSFETs don’t yet meet the mobility in bulk SiC. Several recent experimental studies suggest that, with increasing Al dopant concentration, there is a correlation between further channel mobility reduction and several shallow trap densities. It can therefore be inferred that mobility is being hindered through the trapping of charge carriers by these Al-related defects. To obtain improved future device channel mobilities, the densities of these shallow trap distributions must be minimise, along with their presence within 4H-SiC. This can be done most easily by p-doping with an alternate species. In this thesis, we first investigate the induced lattice distortion, and incorporation and ionisation energies of defects with impurity atoms – Al, B, Be Ca, Cu, F, Ga, In, Mg, Pt, Sc, Tl, Zn - placed on Si and C sites or interstitially, using PBE0-TC-LRC Density Functional Theory (DFT) calculations, to show the p-dopant potential of these fourteen impurities. We find that, although several interstitial Fi positionings possess shallower ionisation and lower incorporation energies than Al, the shallow donor FC defect requires less energy to form. This suggests that F cannot be reliably used for p-doping in place of Al, with calculated ionisation energies confirming that Al, which settles in a Si-substitutional defect, is still the best and most industrially viable p-dopant for 4H-SiC. Due to this finding, attentions turned to identifying the Al-related mobility-affecting defects. Density functional theory (DFT) calculations of AlSiNCAlSi and AlSiOCAlSi defect complexes have found one configuration of the AlSiOCAlSi complex to have a charge transition level and calculated activation energy within the extracted trap level ranges of several of the shallow trap densities. Therefore, it is suggested that these AlSiOCAlSi defects are likely candidates for traps responsible for the channel mobility reduction.
| Type: | Thesis (Masters) |
|---|---|
| Qualification: | M.Phil |
| Title: | Investigating p-doping related impurities within 4H-SiC to improve device channel mobility |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10203520 |
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