多重有序化电子结构的氧化物半导体的制备与性能研究

A trend in the development of semiconducting materials is the introducing of tunable multiply-valued internal state to control the charge transport behavior of the semiconductors. The particular internal state can be resistivity, permittivity, polarization, magnetization, optical transmission, or other properties. The switching process between the internal states can be electric, magnetic, thermal, optical, or other manner. For example, the magnetization is employed to tune the properties of the carrier in spintronics; in the recently developed piezotronics, the inner-crystal piezopotential acts as a gate voltage to form the prototype devices of the field-effect transistor and p-n junction diode; the discovery of ferroelectric photovoltaic effect - a photocurrent is created in ferroelectric materials by ultraviolet light illumination and its direction depends upon ferroelectric polarization-has also received considerable attention. .For the preceding oxides, besides acting as semiconductors, we can consider that an extra ordering is brought into the materials. From this point of view, and following the development of single-phase multiferroic materials, two orders such as ferromagnetic order and ferroelectric order are further suggested to introduce into the oxide semiconductors simultaneously in this proposal. In these proposed materials, the carrier may play as a medium in the coupling effect between magnetic ordering and ferroelectric ordering, which is different from the medium of stress or phonon in conventional multiferroic materials. .The particular materials are focused on epitaxial BiFeO3 thin films, to which the electric and magnetic properties are currently attended as a multiferroic insulator instead of as a semiconductor. ZnO thin films are also involved as a contrast system because of its widely-adjustable properties and the possible application importance. The fabrication of the materials with simultaneous magnetic ordering and ferroelectric ordering is realized by multi-dopant process. The control of bandgap, ferroelectric properties and magnetic properties of the materials will be stressed based on bandgap engineering. The carrier-dependant electric and magnetic properties and the corresponding physical effects induced by the modification of carriers using external electric or magnetic fields will be intensively investigated. The related physical mechanisms for the effects will be detailed and analyzed within the theoretical framework of the coupling between the carrier and the purposely introduced extra electric and magnetic orders.

引入有序结构来控制载流子的输运是半导体材料研究的重要方向：稀磁半导体的磁性受到载流子的强烈调制；最新发现受铁电极化调制的光伏效应，表明半导性的铁电体中存在铁电极化-载流子耦合。本项目从统一的物理原理认识稀磁半导体氧化物和多铁性氧化物，通过多元掺杂使氧化物半导体多铁化以及多铁性氧化物半导化。在BiFeO3,ZnO等外延薄膜中同时引入铁电、铁磁序和载流子。这类材料可存在"铁电-载流子-铁磁"耦合方式，其中受调制的载流子起到媒介作用，以区别于磁电复合材料"铁电-应变-铁磁"的耦合途径和第二类铁电磁体的"铁磁-声子-铁电"耦合途径，从而产生众多新物理效应和应用。.项目研究薄膜生长；建立材料微结构、组分与材料磁、电、半导体等性能的关系；观察载流子控制的铁磁性、铁电极化调制的载流子特性；明确"铁电-载流子-铁磁"耦合方式的微观物理图像；为这类氧化物材料在多功能电子器件中的应用提供理论依据和材料基础。

本课题围绕“多重有序化电子结构的氧化物半导体的制备与性能研究”开展工作，重点关注了以BiFeO3为代表的多铁性氧化物中铁电序、铁磁序与微结构的关系，以及这些有序结构对于材料光学、电学性能的调控。同时研究了其它具有铁电序结构氧化物的制备，铁电、压电性能及其在器件中的应用。项目主要完成了以下三个方面的工作：1，通过固溶掺杂对BiFeO3的铁电、铁磁有序结构及半导体特性进行调控。采用TbMnO3，YMnO3掺杂调控了BiFeO3的禁带宽度，系统研究了固溶体铁电、铁磁性能与掺杂材料种类及掺杂浓度的关系。2，BiFeO3固溶体薄膜的外延生长与外延薄膜的性能调控。通过改变衬底与薄膜的晶格常数匹配程度，调控固溶体薄膜的应力与晶体结构，以及由此而引起的铁电、铁磁性能的变化，确定了薄膜内更大的应力有利于BiFeO3薄膜的自极化效应，研究了外延BiFeO3铁电半导体薄膜的铁电自极化效应及外场控制的铁电极化翻转对于BiFeO3固溶体薄膜光伏效应的调控。3.BiFeO3基、PZT基铁电/压电氧化物陶瓷的制备、性能调控与应用。发展了一种普适性的纳米颗粒制备方法，尤其适用于具有复杂成分的铁电氧化物如掺杂的BiFeO3固溶体。利用该方法制备了LiFeBO3纳米材料并有效提升了其性能。研究了PZT基铁电氧化物陶瓷的掺杂及其在压电能量回收中的应用。