二维层状半导体载流子电场调制与迁移率优化研究

Layered two-dimensional (L2D) semiconductors such as molybdenum disulfide have emerged as attractive candidates for next-generation ultrathin electronics, owing to the concurrence of structural properties of perfect flatness and atomic thickness. Beginning with the insightful understanding on the primary carrier scattering mechanisms in the L2D semiconductors (i.e., Coulomb impurity), this research plan aims to engineer the carrier vertical distribution within the ultrathin L2D channels through a novel dual-gate device structure, for the purpose of reducing impurity scattering intensity, which would further optimize the device performance with integrating the as-established mobility enhancing approaches of surface passivation and dielectric screening into the devices. Several key scientific issues will be addressed on the interfacial characteristics, charge trap states, electric-field modulation, and carrier transport behavior. The relationship of carrier vertical distribution under electric field modulation to impurity/carrier scattering interaction distance, scattering intensity, and mobility magnitude will also be investigated. In order to lay technologically viable foundation for developing next-generation high-performance ultrathin electronics, this project will also be devoted to realizing the high-mobility dual-gated ultrathin transistors and related key fabrication techniques such as surface passivation of high-k dielectrics and van der Waals stacking of heterojunctions.

以二硫化钼为代表的二维层状半导体同时拥有平整表面和原子级厚度，为开发下一代超薄电子器件开辟了新途径。基于对二维层状半导体内载流子的主要散射机理（即界面杂质库仑散射）的深入了解，本项目拟通过栅极电场精准调控载流子纵向分布这一新颖手段来控制载流子/杂质的库仑散射作用距离，达到降低杂质散射强度和提高器件迁移率之目的；结合其它已开发的迁移率优化手段（介质钝化和介电屏蔽等），来全面提高二维层状半导体器件性能。通过理论和实验测试分析，研究异质结构界面特征、电荷陷阱态、外电场调控和载流子行为等关键问题；系统研究栅电场调控下载流子纵向分布对库仑杂质/载流子散射作用距离、载流子散射强度和迁移率大小的影响规律；并依此深入研究用于双栅异质结构的高κ介质表面钝化及介质/沟道/介质结构的制备工艺；研制获得具有高迁移率的双栅超薄晶体管，为发展下一代高性能超薄沟道电子器件提供科学依据和技术基础。

以二硫化钼为代表的二维层状半导体同时拥有平整表面和原子级厚度，为开发下一代超薄电子器件开辟了新途径。基于对二维层状半导体内载流子的主要散射机理的理解，利用栅极电场精准调控载流子纵向分布这一新颖手段，研究了载流子/杂质的库仑散射作用距离对沟道载流子散射强度和器件迁移率的影响。充分考虑沟道载流子分布、介电环境和器件形状因子后，我们对二维原子晶体沟道载流子散射机制作了全面的研究。研究表明，由表面电离杂质和纵向极性声子散射是超薄沟道的主要散射机制。利用平均近似，我们改进了PLO声子的极化电场分布，发现在MoS2中PLO声子散射造成迁移率约100cm2/Vs左右，也实验观察更为吻合。该研究重新定义了二维原子晶体室温的迁移率上限，对晶体管沟道材料的选择具有一定的指导作用。还开发出用于双栅异质结构的高κ介质表面钝化及介质/沟道/介质结构的制备工艺，并基于双栅器件系统，研究了栅电场调控下载流子纵向分布规律及对库仑杂质/载流子散射作用距离、载流子散射强度和迁移率大小的影响。通过变温电学测量等手段，获得了底栅和顶栅两种电调控模式下沟道的迁移率-温度关系。研究表明，二维原子晶体对外界的库仑散射有较强的屏蔽效果，表面库仑杂质的有效作用距离约为1nm。此研究结果对于制备高性能的二维原子晶体异质器件有重要的参考意义。最后，结合其它已开发的迁移率优化手段（介质钝化和介电屏蔽等），获得了具有高迁移率的双栅超薄晶体管，为发展下一代高性能超薄沟道电子器件提供科学依据和技术基础。