外延BaTiO3薄膜的导电性能调控及电荷输运机制研究

The study on the conductivity and charge transport behaviors of the traditional insulating ferroelectric oxides is a cutting edge research topic in the ferroelectric materials community. For the stoichiometric BaTiO3 (BTO), lots of research works have been carried out on its ferroelectric and dielectric properties. However, the work related to the BTO films' conductivity behavior and their corresponding charge transport mechanisms are very rare and not well understood. In this project, we will study how to modulate the conductivity of the BTO film and reveal the charge transport mechanisms embedded in its conductivity behaviors. The main research work will be done as follows: 1) Growth and microstructure characterization of high-quality epitaxial BTO film. 2) Impact of the physical defects (structural defects) and chemical defects (impurities, oxygen vacancy, cation vacancy) on the conductivity and charge transport behaviors of BTO film. 3)Impact of ferroelectric polarization on the conductivity and charge transport behaviors of BTO film. This project will realize the reliable modulation of the BTO films' conductivity among insulator-semiconductor-metallic transport. The charge transport behaviors of BTO films will be well demonstrated, and the physical mechanisms embedded in the charge transport behaviors of conductive BTO film will be revealed.Our work will provide useful theoretical and experimental results for BTO films' applications in novel resistive switcing memory and optoelectronic devices.

对传统绝缘铁电氧化物的导电和电荷输运行为的研究，是当前铁电材料研究领域中具有丰富物理内涵和广泛应用前景的前沿课题。学术界对具有理想原子化学配比的绝缘钛酸钡(BaTiO3) (BTO)的铁电和介电特性已进行了系统研究，而对BTO薄膜的导电行为及电荷输运机制的认识还有待深入。项目拟对外延BTO薄膜的导电行为进行调控，揭示影响BTO薄膜导电行为的电荷输运机制。主要研究内容包括:1) 外延BTO薄膜的高质量生长及微结构表征；2) BTO薄膜中的物理(微结构缺陷)和化学缺陷（杂质离子、氧空位和阳离子空位）对其导电性能和电荷输运机制的影响；3）铁电极化对BTO薄膜的导电和电荷输运的影响机制。本项目将实现BTO薄膜在绝缘体-半导体-金属导电性能间的可靠调控；系统阐释BTO薄膜的电荷输运行为，揭示影响导电BTO薄膜电荷输运的微观物理机制，为拓展BTO薄膜在新型阻变和光伏能源器件中的应用提供理论和实验积累。

传统意义上的铁电氧化物是良好的绝缘体，过去的研究基本上以其铁电性、介电性、压电性展开，而对铁电材料的导电特性，人们关注和了解得甚少。事实上，具有导电特性的铁电氧化物材料，不仅具有丰富的物理内涵，而且在光伏、阻变存储等方向具有广阔的应用前景。是当前铁电材料研究领域一个热门的研究课题。.本项目开展了对外延钛酸钡(BaTiO3 BTO)薄膜的导电和电荷输运行为，电荷输运机理、铁电性与导电性共存、铁电极化调控导电性等方面的研究。我们采用脉冲激光沉积方法，实现了BTO薄膜的高质量外延生长，并对其微结构进行了系统表征；通过输运测试，系统研究了BTO薄膜的外延生长温度(调控其微结构缺陷)、氧空位浓度、不同的Nb和La掺杂浓度、Ba/Ti阳离子空位以及不同衬底对BTO薄膜的导电和电荷输运的影响，实现了其导电性在绝缘-半导体-金属导电之间的可靠调控；揭示了上述各种掺杂情况和不同温度区间的电荷输运机制；揭示了铁电极化对电荷输运的影响并对其BTO薄膜的阻变行为进行了研究。尤为重要的是，本项目揭示了宏观的金属导电和微观的铁电极化在同一La-BTO薄膜中获得，为铁电性和金属性共存这一具有挑战性的理论提供了强有力的实验证据。.本项目的工作，对于理解钙钛矿氧化物中复杂的导电和电荷输运机制，拓展铁电氧化物薄膜在未来新型阻变存储器件和光伏能源器件中的应用，提供了非常好的理论积累和实验积累。