非磁性GeTe/Sb2Te3超晶格薄膜及存储单元磁阻效应及其物理机制基础研究

Giant magnetoresistance up to 2000% has been found in nonmagnetic GeTe/Sb2Te3 superlattice thin films. Novel information storage technology which will combine the technical advantages of MRAM and PCRAM is expected based on this GMR effect. GeTe/Sb2Te3 superlattice thin films and memory cells will be prepared in this project. By optimizing their layer structure and fabrication parameters,the MR of memory cell will be improved. The effect of applied magnetic field on the local structure and bonding status of GeTe/Sb2Te3 interface in the crystallization process will be studied by EXAFS spectra analysis and HRTEM will be employed to investigate the defect microstructures.The GeTe/Sb2Te3 interface model will be built up based on the EXAFS and HRTEM analysis results. Using the First Principle, the effect of applied magnetic field on its electronic band structure, spin density of state and the spin-related scattering will be calculatede and analyzed. The intrinsic magnetoresistance of GeTe/Sb2Te3 superlattice thin film will be investigated in the pulsed high magnetic field up to 55T.The physical mechanism of the GMR effect in nonmagnetic GeTe/Sb2Te3 superlattice thin film will be further studied from both topological insulating properties and magnetism origin in nonmagnetic materials. The expected research achievements of this project will further promote the understanding on the spin transport properties and mechanism in semiconductor materials and devices.

非磁性GeTe/Sb2Te3超晶格薄膜具有高达2000%的磁电阻变化率，基于此磁阻效应有望开发兼具相变存储和磁随机存储技术优势的新型信息存储技术。本项目拟制备GeTe/Sb2Te3超晶格薄膜及存储单元；通过优化GeTe/Sb2Te3超晶格结构和制备工艺，提高存储单元的磁阻变化率；采用EXAFS分析技术研究外磁场对GeTe/Sb2Te3超晶格薄膜相变过程中层间界面局部原子结构及键态结构的影响，并采用HRTEM观测材料缺陷等微观结构；基于EXAFS和HRTEM研究结果构建GeTe/Sb2Te3界面结构模型，采用第一性原理计算分析外磁场对其能带结构、自旋态密度及自旋相关散射的影响；研究0-55T脉冲强磁场中GeTe/Sb2Te3超晶格薄膜的本征磁阻特性；从拓扑绝缘性和非磁性材料磁性起源两个角度深入探讨其磁阻效应物理机制。本项目研究成果将进一步推动对半导体材料及器件自旋输运特性及机理的深入理解。

非磁性GeTe/Sb2Te3超晶格薄膜具有高达2000%的磁电阻变化率，基于此磁阻效应有望开发兼具相变存储和磁随机存储技术优势的新型信息存储技术。本项目制备了GeTe/Sb2Te3超晶格薄膜及存储单元；通过优化GeTe/Sb2Te3超晶格结构和制备工艺，制备的存储单元的磁阻变化率可达6083%；采用EXAFS分析技术研究了外磁场对GeTe/Sb2Te3超晶格薄膜相变过程中层间界面局部原子结构及键态结构的影响，并采用HRTEM观测了材料界面缺陷等微观结构；基于EXAFS和HRTEM研究结果构建了GeTe/Sb2Te3界面结构模型，采用第一性原理计算分析了外磁场对其能带结构、自旋态密度及自旋相关散射的影响；研究了强磁场中GeTe/Sb2Te3超晶格薄膜的低温磁电阻特性；从拓扑绝缘性和超晶格界面无序两个角度深入探讨了其磁阻效应的物理机制。.理论计算和电子衍射实验证实制备的GeTe/Sb2Te3超晶格薄膜为具有范德华间隙的层状结构，Te 悬挂键在层间界面分布密度较高，使得原有范德华间隙转变为层间空位集中分布区域，且子层界面因Te悬挂键的存在和不同原子混杂具有层间无序性。层间无序程度可通过改变子层组分及制备工艺参数进行有效调节。低温电输运研究表明：多界面的存在决定了GeTe/Sb2Te3超晶格薄膜中存在多个且发生相互耦合的界面拓扑态，这是其具有磁阻效应的基础物理机制；层间无序性不会破坏超晶格中的拓扑态但会改变界面拓扑态间的耦合强度。层间无序调控下的直接隧穿与振荡隧穿输运共同作用模型可以很好地解释层间无序性对GeTe/Sb2Te3超晶格薄膜界面拓扑态间的耦合强度的影响。.本项目研究成果为进一步有效调控GeTe/ Sb2Te3超晶格薄膜的磁阻特性提供了理论依据，也为将来进一步利用GeTe/ Sb2Te3超晶格薄膜的磁阻特性开发新型存储器件奠定了基础。.