Oxide electronics, also referred to as transparent electronics, is an important emerging area, notably for the development of thin film transistors (TFTs) and more complex electronic circuits. The significant research interest in this field has been spurred by the enormous success of n-type oxide semiconductors, specially amorphous oxide semiconductors, in particular gallium-indium-zinc oxide (InGaO3(ZnO)5, or GIZO). The successful application of n-type oxides to TFTs has motivated the interest in p-type oxide based semiconductors also to be applied to TFTs or to complementary metal-oxide semiconductor (CMOS) technology. However, until now there is a lack of p-type oxide semiconductors with performance similar to that of n-type oxide. In fact, for p-type oxides, the carrier conduction path (valence band) is mainly formed from the oxygen p asymmetric orbitals. However, due to the ionicity of the metal-oxygen bond in most of metallic oxides, this leads to the formation of a deep acceptor level which limits the hole mobility. Among the different metallic oxides, Cu(I)-based oxides exhibit one of the lowest ionic character. These compounds are therefore one of the most promising candidates as p-type transparent semiconductors.
Within this context, in order to develop low-temperature processed materials adapted to thermal sensitive substrates, Sr-doped Cu2O thin films grown by plasma- or UV-assisted metal-organic chemical vapor deposition (MOCVD) will be investigated. The optimization of the growth conditions will be performed by a detailed characterization study using a wide range of standard physicochemical analysis techniques (X-ray diffraction; scanning and transmission electron microscopy; energy- and wavelength-dispersive X-ray, Fourier-transform infra-red and Raman spectroscopies), which will be complemented by dedicated advanced elemental analyses such as time-of-flight elastic recoil detection or atom probe tomography. Transparent p-n junction devices will be subsequently fabricated by depositing the Sr:Cu2O films on well-known n-type layers such as Al:ZnO or F:SnO2, and their transport properties as well as their optical transmittance will be measured. The interpretation of the electrical characteristics will be supported and guided by numerical simulations of the semiconducting heterostructures.
This PhD project will be carried out in the framework of a close collaboration between the LMGP (Laboratoire des Matériaux et du Génie Physique) in Grenoble (Grenoble INP), France, and the Laboratory for solid-state physics, interfaces and nanostructures of the University of Liège (Department of Physics), Belgium. The MOCVD growth and the physicochemical analysis will be performed in Grenoble while the electrical characterization of the fabricated diodes, as well as the numerical simulation of the device characteristics, will be realized in Liège. Imec, the industrial partner and a world-leading research center for nano-electronics located in Leuven, Belgium, will provide the advanced elemental analyses. The collaboration between these partners should lead to a much better understanding of the material properties which play significant roles (defect density, electrically active dopant concentration, interface quality …). This should also help to better optimize the growth parameters and the performance of the transparent pn junction diodes.
Project Partners and their Roles
Laboratoire des Matériaux et du Génie Physique (LMGP), Grenoble Institute of Technology (G-INP), France: MOCVD deposition set-ups, physical and structural characterization methods (GIXRD, TEM, SEM, Raman and FTIR spectrometry, spectro-photometry…)
Laboratory for solid-state physics, interfaces and nanostructures, University of Liège (Department of Physics), Belgium: electrical characterization and numerical simulation of the device characteristics.
Industry partner: IMEC, Leuven, Belgium
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