Proceedings of nanoGe Fall Meeting19 (NFM19)
DOI: https://doi.org/10.29363/nanoge.nfm.2019.214
Publication date: 18th July 2019
The chemical storage or solar energy in form hydrogen through photoelectrochemical water splitting is a promising method that has the important advantages of being environment friendly and free from carbon dioxide emission. Metal oxides are promising candidates for photoanode but their low efficiency is suspected to be due to strong electron-hole recombination. The carrier lifetime being one of the important limiting processes, its determination appeared as a mandatory step in the understanding of the underlying phenomena and eventually defining strategies to overcome this shortcoming. We have investigated the electron hole recombination dynamics in different oxide photoanodes using time-resolved photoelectron spectroscopy (TR-PES) utilizing a laser-pump / synchrotron – radiation (SR) probe method at different time resolutions. Upon photoexcitation, in the presence of a surface depletion layer (for an n-type semiconductor), electrons are promoted into the conduction band and migrate into the bulk, inducing a positive surface photovoltage (SPV). This surface charge induces a reduction of kinetic energy of photoelectrons measured by PES. The reverse phenomenon (shift toward higher kinetic energy) occurs for p-type semiconductors [1]. Therefore, the time-resolved energy shift of the photoemission spectra caused by the surface photovoltage effect is expected to be linked to the charge dynamics.
We have studied the carriers’ lifetime in Ti-doped Fe2O3 as a function of the Ti doping level. The samples were thin epitaxial films prepared by atomic oxygen plasma assisted molecular beam epitaxy deposited on single crystalline Pt(111) [2]. We will show that the electronic structure and lifetime are strongly influenced by carbon contamination while Ti doping is less determinent.
In a second part we will report on the influence of an internal electric field on carrier’s lifetime in ferroelectric BaTiO3 thin films. The samples were BaTiO3 thin epitaxial films prepared by atomic oxygen plasma assisted molecular beam epitaxy deposited on single crystalline Pt(100) with different orientation of electrical polarisation. We observe that the SPV value and the time decay strongly depends on polarisation orientation.
All these results were correlated with photoelectrochemical measurements on the same samples.
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