Of Gan Substrate Composite Buffer Layer Induced Epitaxial Growth Of Bst Perovskite Oxide Thin Films

Pervoskite complex oxide materials such as BST- series materials are one of the most important functional materials. Such material is the key part of passive devices in microwave and RF circuits due to its outstanding multifunctional properties in ferroelectric, dielectric field. The heterostructure, which integrated the pervoskite thin films with GaN substrate (as the third generation semiconductor), can fulfill the passive-active integrated devices, leading to the high multifunctional performance and increasing the level of integration. However, because of the large difference both in growth behavior and crystal structure between the pervoskite oxide and gallium nitride material, it is difficult to obtain the epitaxial thin films; Moreover, due to the anisotropy properties of pervoskite materials, it requires to control of the orientations of epitaxial films on GaN substrate. Therefore, it is crucial to explore a method to fulfill the epitaxial growth and orientation control of the pervoskite films on GaN substrate.In this thesis, SrTiO3 with cubic pervoskite have been analyzed. Then, using the multi-oxide-buffer-layer as TiO₂, YSZ, CeO₂ and YBCO layers, STO in three typical orientations had been epitaxially grown on GaN substrate, which was in [001], [110] and [111] respectively. Further, BST films in such orientations were integrated with GaN using same process conditions.Firstly, the a-axial oriented YSZ and CeO₂thin films with fluorite structure were prepared by pulsed laser deposition method. The dependence of the crystalline quality and crystal orientation of such films upon the process parameters (deposition temperature, oxygen pressure, pulse laser energy intensity) were systematically studied.Secondly, the STO films in [001] and [110] orientations have been grown on GaN substrate using multi-buffer-layers. The modeles in growth kinetics of STO films have been build up. Further, (110)-oriented STO films were obtained using YSZ/TiO₂ buffer layers; (001)-oriented STO films were prepared using YBCO/CeO₂/ YSZ/TiO₂ buffer layers, and the epitaxial orientation has been confirmed: STO (200) [110]// YBCO(001)[110] //CeO₂ (200) [010]// YSZ (200)[010] //GaN(0001)[11-20]. Moreover, the growth behavior of STO has been determined by both of the interface stress and ionic bonding when STO growing on fluorite surface.Finally, BST films in three typical orientations have been integrated with GaN substrate using the multi-oxide-buffer-layers technique. Further, the electric properties of such original integrated devices have been anglicized.