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Photoemission studies of ex-situ and in-situ surface cleaning and electronic properties of ZnO surfaces

Kumarappan, Kumar (2015) Photoemission studies of ex-situ and in-situ surface cleaning and electronic properties of ZnO surfaces. PhD thesis, Dublin City University.

The aim of this research project was to undertake the surface characterisation of (0001)- Zn, (000-1)-O polar and (10-10), (11-20) non-polar ZnO surfaces by x-ray photoelectron spectroscopy (XPS) and to develop surface cleaning procedures to make these surfaces suitable for subsequent device processing. Conventional XPS and synchrotron radiation based photoelectron spectroscopy (SRPES) were used to undertake binding energy calibrations, estimations of surface contamination, stoichiometric analysis and electronic band alignment measurements for the different ZnO surfaces. A wide range of cleaning procedures including ex-situ organic solvent cleaning, in-situ ultra-high vacuum (UHV) annealing, in-situ atomic hydrogen and atomic oxygen cleaning as well as in-situ high temperate molecular oxygen annealing treatments were systematically investigated and evaluated as to their effectiveness at preparing contamination free surfaces. The ex-situ wet chemical cleaning resulted in only a small reduction in the carbon contamination signal and a corresponding increase in the surface hydroxide signal. On all ZnO surfaces investigated, the contamination was reduced at different rates, depending on the surface termination. The in-situ surface cleaning studies showed that while in general it is possible to remove the carbon contamination by a variety of methods, the surface hydroxide species cannot be removed, due to the bond strength of O-H. It was found that the effective carbon removal temperature for the ZnO surfaces using atomic hydrogen cleaning was 600 °C, using molecular oxygen thermal cleaning it was 700 °C and for atomic oxygen, the cleaning temperature was 400 °C. As the result of removing carbon contamination on all ZnO surfaces, the natural surface downward banding was reversed into upward band bending.
Item Type:Thesis (PhD)
Date of Award:November 2015
Supervisor(s):Hughes, Greg
Uncontrolled Keywords:ZnO
Subjects:Physical Sciences > Thin films
Physical Sciences > Nanotechnology
Physical Sciences > Semiconductors
DCU Faculties and Centres:DCU Faculties and Schools > Faculty of Science and Health > School of Physical Sciences
Use License:This item is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 3.0 License. View License
ID Code:20827
Deposited On:20 Nov 2015 14:58 by Gregory Hughes . Last Modified 19 Jul 2018 15:06

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