Crystalline perovskite epitaxial growth on germanium (001) by atomic layer deposition
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Crystalline perovskites (ABO3) have aroused widespread attention in material science due to their multiple properties. This research uses atomic layer deposition (ALD) to achieve perovskite oxides (ABO3) deposition on Ge (001) for gate oxide applications in microelectronics devices. In particular, this work is mainly focused on the study of crystalline Sr-based perovskites SrMO3, where M = Ti, Zr, Hf. In this research work, the mechanism for the initial growth of perovskites on Ge by ALD has been studied. High resolution scanning transmission electron microscopy (STEM) images have shown that both of molecular beam epitaxy (MBE)-grown BaTiO3 films and ALD-grown SrHfO3 films have the same interface structure, which has a 2×1 periodicity and with the alkaline earth metal (AEM) atoms between the Ge dimer rows. This result indicates that the ALD growth proceeds by forming the same Zintl-template layer that is purposely formed in MBE through formation of a 0.5-monolayer (ML) exposure to the AEM. The in situ XPS analysis has shown the same surface core level shift (SCLS) behavior results from half-cycle Sr or Ba precursor dosing on a bare Ge (001) surface as is observed following 0.5 -ML Sr or Ba exposure on Ge by MBE. These observations support the conclusion drawn from the STEM images. Based on the previous study of SrTiO3 (STO) and SrHfO3 (SHO) on Ge (001), there is a trade-off between dielectric constant and leakage current in STO and SHO. This research has also studied SrHfxTi1-xO3 (SHTO) films with different Hf content x to see how composition and lattice constant affected the crystallization behavior. Crystalline SrZrO3 films have also been deposited by ALD on Ge. The C-V and I-V measurements indicate that the SrZrO3 yield the best results for dielectric properties compared to STO, SHO and SHTO. A new combined approach of oxygen plasma pre-treatment, Zintl template formation and atomic deuterium post treatment has been applied on this work to minimize the interface trap density, which has achieved 8.56×1011cm-2eV-1.