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Optoelectronic properties of ferroelectric semiconductors
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Zhang, Hangbo (2022) Optoelectronic properties of ferroelectric semiconductors. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3877493
Abstract
The optoelectronic properties, such as bulk photovoltaic effect and photoconductivity, of ferroelectric semiconductors have been attracting enormous attention, due to their promising application in solar cells and other multi-functional devices. These exciting findings, such as the highly-conductive domain walls and flexo-photovoltaic effect, reveal the fact that there might be other undiscovered and fascinating phenomena in the field of optoelectronics.
The emergence of important physical properties of a semiconductor could be from the defects, including structural defects and point defects that naturally exist in the system or are artificially introduced. For example, defects could increase/decrease the carrier density and modify the electronic structure, thus changing the carrier transport properties. With this being the background, we first focused our study on the bulk photovoltaic effect of the ferroelectric domain walls. We showed that the domain wall can largely enhance the photovoltaic current via an interaction with the defects.
We further investigated the effect of the heterointerface of a thin film, as the interface usually shows unexpected physical properties. We started by comparing the optoelectronic properties of bismuth ferrite thin films grown on different substrates and found that the strontium titanate could provide a highly conductive path at its surface with bismuth ferrite. We proved that this is due to the significant defect density and high carrier mobility of strontium titanate. Inspired by this exciting result, we further investigated the physical properties of strontium titanate in its heterostructures. Results showed that the interface between strontium titanate and other oxides is polar when the temperature is down to the onset of the quantum paraelectric phase of strontium titanate. We demonstrate that the principle of the emergence of the polar interface is due to the generic band bending at the interface of two dissimilar materials.
In the last part of the thesis, we investigate the magneto-photocurrent effect in bismuth ferrite. This has not been ever studied but is urgently needed, because spin-current and ferromagnetism-tuned physical properties are critical for studies of spin-charge conversion systems. We demonstrate that an unprecedented hysteretic magneto-photocurrent behaviour exists in the bismuth ferrite-terbium scandate system, due to the potential ferromagnetism texture at the interface. We purpose a plausible model that is based on the spin galvanic effect and Hanle spin precession, and successfully explains the ferromagnetism-related spin scattering behaviours.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QC Physics T Technology > TA Engineering (General). Civil engineering (General) |
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Library of Congress Subject Headings (LCSH): | Ferroelectricity, Semiconductors -- Electric properties, Photovoltaic effect, Optoelectronics | ||||
Official Date: | May 2022 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Physics | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Alexe, M. (Marin) | ||||
Format of File: | |||||
Extent: | vi, 124 pages : illustrations (colour), charts (colour) | ||||
Language: | eng |
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