负能隙可调新型半金属探索：结构设计、薄膜生长与物性研究

Semimetals and gapless semiconducgtors are quite rare. This fact imposes a strong constraint on the implementation of such materials. To exploit the new lattice sites in addition to the lattice of the original matrix is a particular way of doping, which can radically modify the electronic structure of the solids, it thus holds the promise to give rise to a series of novel gapless semiconductors and semimetals of a tunable negative band gap. The nitride Mn3N and Cu3N are a solid of the anti-ReO3 structure. By properly choosing some extra atoms to occupy the cell centers of the original cubic lattice, which are previously unoccupied, it is possible to alter the band gap to a very large extent that in these series of ternary solids one can find some gapless semicondutors and also semimetals of a tunable negative band gap. With the current project, we intend to grow Mn3NMx and Cu3NMx (M= Mn, Cu，Ag, Pd,Zn,etc.) thin films by using reactive cosputtering, pulsed electron deposition and nitrogen plasma -assisted atomic layer deposition, to search for gapless semiconductors and semimetals of tunable negative band gap. The composition depdence of bandgap will be determined, the semiconductor-semimetal transition, the temperature coefficient of resistance, the (magnetic) transport behavior, and the response to externally applied fields will be investigated, aiming at particularly finding out novel excitonic insulator, magnetic semimetals and also structures that showing negative differential resistance. The photoelectric and photothermal transition of the multilayers of wide tunable bandgaps of the Mn3NMx and Cu3NMx based solids, the tunneling enhancement effect of such a semimetal layer in the tunneling junction will be measured. Finally, on the overall evaluation of the properties in those solids, some semiconductor-semimetal devices based on new working principles will be conceived and tested.

半金属和零带隙半导体很稀有，这限制了它们在器件中的应用。在固体原有晶格以外开辟新格点的掺杂方式，能对固体的电子结构造成根本性的改变，提供了实现和调节负能隙的新途径。Mn3N、Cu3N具有反ReO3结构，选择合适的额外金属原子占据母体立方晶胞原先为空的中心位置，可以实现固体能隙的大范围调节，获得系列的新型零带隙半导体和负能隙可调半金属。本项目拟采用共溅射法、脉冲电子束烧蚀法和等离子体辅助原子层沉积法获得Mn3NMx, Cu3NMx 基(M=Mn,Cu,Ag,Pd,Zn等）零带隙半导体和能隙可调半金属薄膜，确定能隙对组分的依赖关系，研究该体系固体的半导体-半金属相变、电阻温度系数、输运行为、外场响应等性质，找寻表现负微分电阻的体系、激子型绝缘体及磁性半金属；研究负能隙可调多层膜结构的光电、光热转换，半金属层对隧道结隧穿电流的增强效应，并综合考虑该类固体的特殊物理性质，设计新的半导体-半金属器件

天然的半金属和零带隙半导体很稀有，在固体原有晶格以外开辟新格点的掺杂方式，可提供实现和调节负能隙的新途径。Mn3N、Cu3N等具有反ReO3的结构，若选择合适的额外金属原子占据母体立方晶胞原先为空的中心位置，可以实现固体能隙的大范围调节，获得系列的新型零带隙半导体和负能隙可调半金属。本项目的研究内容就是制备系列的Mn3NMx, Cu3NMx晶体薄膜，通过扩展新格点的方式实现不同程度的掺杂，研究它们的导电行为、对外加温度和电磁场等外场的响应行为。特别地，研究所获得的Mn3NMx, Cu3NMx基磁性半金属固体的磁阻效应，找寻具有自旋玻璃行为的结构。项目的目标在于研究固体能隙调节的机制和零带隙附近固体性质的变化，获得具有恒电阻率和新颖金属-半导体/半金属-半导体相变的材料。经过三年多的努力，我们发现三元系Cu3NMgx (x< 0.32) 的带隙随掺杂浓度的提高逼近0但依然保持半导体行为；在Mn3Mn1−xPdxN (x< 0.36)体系中获得了电阻率变化在一个数量级内的金属-半导体相变，这是首次有类似行为的报道；在Mn3NMn1−xAgx体系中获得了50-200 K之间大温区内恒电阻率材料。 这些结果不仅增进了我们关于固体性质的知识，而且可提供用于制作新型光电器件的材料。