1. Modification and Characterization of Transparent Oxides
Using Ion Beam
Candidate : Emmanuel Njumbe Epie, Advisor : Prof. Wei-Kan Chu
Date: November 14th 2016
Time: 2:30 pm
Location: SR1-410
Abstract
The addition of impurities to semiconductors and some insulators to control their properties
has led to great advances in the electronic industry. As the applications of mobile devices
continue to expand, there is a growing need for increased capability and miniaturization. This has
generated interest in the design and characterization of materials capable of combining impressive
optical and electronic properties. Among these materials of interest are wide band gap oxides
also known as transparent oxides (TO). Because of their unique properties, TO are suitable for
the development of hard, robust and energy efficient devices. The relatively large width of their
forbidden energy gap (Eg > 3.1 eV ) provides great opportunities for band modification and hence
a potential for diverse applications such as photocatalysis, fabrication of novel opto-electronic
devices for emitting and sensing purposes, etc.
In this work, we have utilized ion implantation and ion beam induced luminescence, also called
ionoluminescence (IL), to respectively modify and characterize the optical properties of single
crystalline SiO2, Al2O3 and ZnO. Our results show significant modifications in the structural,
optical absorption and emission properties of these TO, directly establishing correlation with
specific point defects. Based on our results and recent density functional theory calculations,
we have proposed an energy level scheme for native point defects in ZnO. Additionally, we have
proposed recommendations for efficiency enhancement of ZnO assisted photocatalysis. We have
also demonstrated that colour center formation in sapphire is due to dynamic competition between
defect creation and recombination. Finally, we have successfully synthesised and characterised
artificial ruby. This work provides new perspectives for the fabrication and characterization of
TO related opto-electronic devices.
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PhD Defense