Solution based synthesis and electronic characterisation of interface controlled amorphous oxidic multilayer films
Physical Chemistry of Solids and Surfaces, Material Characterisation
Final Report Abstract
Electronic devices such as metal-insulator-semiconductor capacities or field effect transistors consist of multilayered sequences of nanoscalic metal oxides. Understanding and improving the functionality in such constructs requires knowledge of constitution, microstructure as well as defect chemistry. This is especially the case for materials which are deposited by solution-based techniques. Commonly point defects and inhomogeneity with respect to microstructure or morphology play a more significant role than in comparison to gas phase deposition. On the other hand, solution deposition can provide procedural advantages like low instrumental effort as well the possibility for the coating of large areas. In the present investigation the comprehensive characterization of point defects and microstructure of insulating or semiconducting layers by positron annihilation spectroscopy was carried out successfully. This allows to relate changes of electronic performance parameters in dependence on the processing conditions. Thereby, two techniques were employed, i.e. Doppler-broadening spectroscopy as well as positron life measurements. In this way the impact of the organic component could be elucidated in the manufacturing of aluminium oxide films from aluminium nitrate and additional reduction agents such as methyl carbazate. In fact, layers can also be obtained by thermal composition of aluminium nitrate alone and without further additives. Such layers exhibit significantly inferior dielectric and insulating properties in comparison to counterparts obtained from mixtures. The diverging electrical behavior can be attributed to a higher porosity and the formation of mesopores in particular. The latter can be suppressed, however, by addition of suitable organic additives. Supplementary investigations were able to show that condensation reactions take place in solutions of mixtures of aluminium nitrate and methylcarbazate, which favour gelation and are thus advantageous for the overall ceramisation process. In a further example the semiconducting properties of zinc oxide were investigated. Using positron annihilation spectroscopy the existence and dominating influence of larger defect clusters could be established. In such entities one or more oxygen vacancies are attached to immediately neighboring cation vacancies. Such these vacancy clusters [VZn-(VO)n] are acceptor dopants, which cause holes in the valence band of ZnO and thus cause a significant drop in the electronic carriers. This can be directly followed by experimentally determined performance parameters of field effect transistors.
Publications
- Chem. Eur.J., 2021, 27, 5422-5431 “Zinc oxide defect microstructure and surface chemistry derived from oxidation of metallic zinc. Thin film transistor and sensoric behaviour of ZnO films and rods.”
R.C. Hoffmann, S. Sanctis, M.O. Liedke, M. Butterling, A. Wagner, C. Njel, J.J. Schneider
(See online at https://doi.org/10.1002/chem.202004270) - Dalton Transactions, 2021, 60, 8811–8819 “Solution synthesis and dielectric properties of alumina thin films: Understanding the role of the organic additive.”
R.C. Hoffmann, M.O. Liedke, M. Butterling, A. Wagner, V. Trouillet, J.J. Schneider
(See online at https://doi.org/10.1039/d1dt01439k)
