晶格应变对钙钛矿结构锡酸盐基稀磁半导体性质影响研究

Due to their rich physics and their promising properties for application, perovskite oxides and dilute magnetic semiconductors have attracted much attention in recent years. Perovskite stannates ASnO3(A=Ba, Sr and Ca) are wide band gap semiconductors. The high mobility achieved in these materials makes them promising candidates for transparent conductive electrodes in all-perovskite devices. Recently, there have been many attempts to fabricate ASnO3-based dilute magnetic semiconductors and reported room-temperature ferromagnetism in them. Lattice deformation is ubiquitous in all-perovskite devices and dilute magnetic semiconductors. On the other hand, it has been found that the physical properties of undoped ASnO3 are sensitive to lattice strain. In this proposed project, we shall systematically investigate the influences of lattice deformation on the physical properties of ASnO3-based dilute magnetic semiconductors. Experimentally, lattice strain of different types and with various magnitudes would be introduced and the structural, optical, electrical and magnetic properties would be characterized in detail by using various techniques, including X ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectra, optical transmission spectra, Hall effect, magnetoresistance, magnetometry measurements and etc. The effects of lattice strain will also be explored by using first-principle calculation. The combination of experimental and theoretical studies shall reveal the effects of lattice strain in ASnO3-based dilute magnetic semiconductors and their underlying mechanisms. It would also provide a way for strain modulation. It is expected that the successful implementation of this project would be helpful for revealing the origin and mechanism of ferromagnetism in dilute magnetic semiconductors as well as providing a reference for the development of ASnO3-based devices.

钙钛矿结构氧化物和稀磁半导体因为蕴含丰富物理和具有重大应用潜力而受到关注。钙钛矿结构锡氧化物ASnO3(A=Ba, Sr 和Ca等)是宽禁带半导体，可以实现高迁移率，是全钙钛矿器件中透明导电电极的理想材料。近来有研究尝试制备基于ASnO3的稀磁半导体。考虑到晶格应变在全钙钛矿器件和稀磁半导体中普遍存在，加之ASnO3自身物理性质对晶格应变相当敏感，本项目拟系统研究晶格应变对ASnO3基稀磁半导体的影响。实验上，引入各种应变，综合运用X射线衍射、透射电镜、光电子能谱、拉曼光谱、吸收光谱、霍尔效应和磁性测量等多种手段，研究晶格应变对其结构、光学、电学和磁学等性质的影响；理论上，基于第一性原理计算，加载不同应变，研究其影响；通过实验与理论相结合阐明应变的作用规律和机制，获得应变调控的方法。本项目的顺利实施有助于澄清稀磁半导体磁性来源，也为基于ASnO3的器件提供理论与技术基础。

钙钛矿结构氧化物具有很多有趣的性质，比如铁磁性、铁电性、压电性、庞磁电阻效应、光伏特性、半金属性、高温超导和多铁性等等。这些特性既涉及物理学基本问题，又为新功能器件提供素材。通过掺杂或者复合等手段在一种器件中实现多种特性共存并实现有效控制，会增强这些材料的应用前景。本研究团队围绕这一主题，开展了一系列研究。主要结果如下：（1）系统研究了晶格应变对系列过渡金属（Co、Mn、Cr、Fe和Ni）掺杂BaSnO3性质的影响，发现应变会影响电子结构。掺杂体系的磁性及其随应变的变化，取决于很多因素，比如掺杂的元素、掺杂的浓度、应变的类型和应变的大小等。除了Mn掺杂BaSnO3的磁矩不随掺杂浓度和应变而改变，在其余体系中均发现应变和掺杂浓度对磁性的影响。掺杂浓度也会影响应变的调控规律。发现通常磁性在小的晶格应变下稳定，改变磁性通常需要大的应变。（2）在钙钛矿结构基片SrTiO3上外延生长了W膜，发现应变诱导多子反型。结构分析揭示了一种特殊的外延生长方式。输运特性测量发现多数载流子的反型取决于晶格应变和温度。第一性原理计算发现晶格应变造成穿过费米面的能带形状产生改变。（3）在钙钛矿太阳能电池中，得到了圆柱孔阵列中光吸收随周期和填充因子变化的规律，并在优化的基础上提出可以进一步提高光吸收圆柱孔-正弦曲面复合结构。（4）制备了高质量钙钛矿氧化物异质结La0.1Ca0.9MnO3-SrTiO3:Nb，在全温度范围具有很好的整流特性，其开路电压显著高于一般p型钙钛矿锰氧化物与SrTiO3:Nb形成的异质结。（5）研究基于钙钛矿结构BaTiO3的铁电隧道结，揭示了BaTiO3厚度对铁电稳定性的影响，得到了不同电极与界面对磁性、铁电性和磁电耦合的影响规律。本项目为丰富钙钛矿结构材料与器件的功能性和可调控性做出了有益探索。