Bonyadi, Yeganeh (2019) Fabrication and analysis of 4H-SiC diodes. PhD thesis, University of Warwick.

PDF WRAP_Theses_Bonyadi_2019.pdf - Submitted Version Embargoed item. Restricted access to Repository staff only until 19 March 2022. Contact author directly, specifying your specific needs. - Requires a PDF viewer. Download (10Mb)

Request Changes to record.

Abstract

Despite the excellent electrical and thermal properties of 4H-silicon carbide (SiC) and the advancements in the field of 4H-SiC epitaxial growth, the existence of defects in the material can considerably reduce the electrical performance of the SiC power devices. Defects can result in low carrier lifetime affecting the on-state resistance of bipolar devices, such as PiN diodes, and increased leakage current affecting the reverse blocking performance of power devices, such as Schottky diodes. A commonly found surface morphological defect in available 4H-SiC substrates is the triangular defect. In this thesis, the formation mechanism of this defect and its impact on the electrical performance of the fabricated 4H-SiC PiN diodes is discussed. 4H-SiC PiN diodes were intentionally fabricated on the triangular defects and in areas with no visible morphological defects. The devices were then packaged and tested to assess the impact of these defects on the resulting on-state and reverse leakage characteristics. It was shown for the first time the impact of triangular defects on switching characteristics of 4H-SiC PiN diodes fabricated on- and off-defects. Moreover, triangular defects were characterised using methods including AFM, SEM, Photoluminescence and HRTEM. Other complex structures were observed on the triangular defect using HRTEM such as double positioning boundary (DPB), which resulted in a leakage path through the drift region of the devices and increased the leakage current.

Furthermore, this thesis focuses on the fabrication and analysis of 4H-SiC power diodes for high voltage applications with particular focus on improving the performance of 4H-SiC SBDs using a novel metal-semiconductor interface treatment and 4H-SiC PiN diodes using high temperature processing techniques to improve the carrier lifetime, on-state resistance and conductivity modulation of the diode. Carrier lifetime enhancement in 4H-SiC PiN diodes in this thesis was achieved using a combined high temperature oxidation and successive argon annealing process at 1550°C for 1 hour. This resulted in an increase of nearly 45% of the reverse recovery current and approximately 40% of the carrier lifetime. The findings of this study could be potentially used for other 4H-SiC bipolar devices such as IGBTs, BJTs and thyristors.

This thesis has also investigated the impact of various surface passivation treatments to improve the quality of the 4H-SiC surface and the metal-semiconductor interface using Mo/Ti, and Ni-4H-SiC Schottky diodes. The most significant outcome of this investigation was the performance of P2O5 treated Mo/SiC Schottky diodes which retained a barrier height equivalent to that of titanium, but with a leakage current lower than any Ni diode, seemingly combining the benefits of both a low- and high-SBH metal. Furthermore, P2O5 treated Mo/SiC Schottky diodes were the only diodes to undergo any significant leakage current reduction after any of the pre-treatments exhibiting exceptionally low leakage, even at 300°C. XPS and SIMS analysis on all Mo/SiC SBDs revealed that the stoichiometry of the SiC underneath the contact was enhanced using P2O5 treatment and that traces of P2O5 were found after removal of the passivation layer and post-treatment metallisation. It was also found that the Mo-4HSiC interface on the P2O5 treated sample was very sharp and uniform compared to the untreated sample where Mo-SiC interface looks uneven and cloudy. The developed novel metal-semiconductor interface treatment can be potentially used for MOS interface improvements.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	T Technology > TK Electrical engineering. Electronics Nuclear engineering
Library of Congress Subject Headings (LCSH):	Silicon carbide -- Electric properties, Diodes, Semiconductor, Semiconductor-metal boundaries, Diodes, Schottky-barrier
Official Date:	October 2019
Dates:	Date Event October 2019 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	School of Engineering
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Mawby, P. A. (Philip A.) ; Gammon, P. M.
Format of File:	pdf
Extent:	xx, 305 leaves : illustrations (some colour)
Language:	eng

Request changes or add full text files to a record

Repository staff actions (login required)

View Item