同质异构结中自发极化相关的电荷裁剪效应的电子显微研究

This proposal plans to quantitatively characterize the spontaneous polarization induced charge tailoring effect, which exists in heterocrystalline junctions within III-V and II-VI compound semiconductor nanocrystals. The off-axis electron holography, Cs-corrected high-angle annular-dark-field imaging, and Cs-corrected high resolution electron imaging techniques will be applied to achieve this purpose. For compound semiconductors, only structures without center of inversion possess spontaneous polarization. The values of spontaneous polarization averaged over areas at nanometer scale and their variations along interface normal would be characterized, based on which the dependence of spontaneous polarization on the structural parameters could be obtained. This information can act as the experimental basis for controlled device fabrication in the near future. Moreover, the Supercell approach, Berry phase approach and other possible methods will be applied to those materials, and the calculated values will be compared with values obtained from experiments. The approach most suitable for heterocrystalline junctions at nanoscale could be found in this way. Through combined utilization of multiple experimental techniques and possible simulation approaches, the atomic structures could be effectively related to local electronic behaviors, which is significant for tailoring charges at nanoscale.

本项目拟采用离轴电子全息、球差校正高角环形暗场像、球差校正高分辨像等多种先进的电子显微学表征手段，对III-V和II-VI族化合物半导体纳米材料中常出现的同质异构结的自发极化相关的电荷裁剪效应进行定量表征。通过对一系列半导体材料中无对称中心的纤锌矿结构（或具有不同堆垛顺序的其他多型体）自发极化强度的纳米尺度平均值及沿界面法线的变化曲线的测定，获取自发极化强度对无对称中心结构特征参数的依赖关系，为未来的可控器件研究提供实验基础。同时结合超单胞法、Berry phase等多种模拟计算方法获取自发极化强度值并与实验值进行对比，获取最适合于纳米尺度同质异构结中无对称中心结构的模拟计算方法。通过多种实验表征手段以及结合相关理论模拟计算，将材料的原子结构与电学性能进行关联研究，以期深入理解同质异构结的结构性能关系，有效指导裁剪电荷分布，具有很重要的现实意义。

该项目主要依托离轴电子全息、球差校正高角环形暗场像等先进的电子显微学表征手段，围绕III-V和II-VI族半导体纳米材料中常出现的同质异构结，及相应由无对称中心的纤锌矿结构带来的自发极化效应进行了定量表征，如从原子尺度定量表征了InAs纳米棒中多型体界面的极化场分布及其受界面应力的影响情况；在InAs（III-V）纳米棒中观察到两种相反构型位错核心及其相应应变场分布；从原子尺度表征了ZnSe（II-VI）纳米螺旋中同时存在的极性连续和极性反转效应等。此外，该项目还支持了若干纳米材料光电器件的合成及应用研究：如SnO2纳米球的贋负光电导效应，暖白光LED的实现，KxWO3纳米片中阳离子无序有序转变，单层MoS2光电晶体管中的响应率增强效应，以及非极性面n-ZnO/p-AlGaN紫外LED在插入本征ZnO层后性能增强的微观机理研究等。复合半导体纳米材料原子尺度的结构性能相关研究，以及宏观光电材料及器件相应光电性能的微观机理研究对未来高性能光电器件设计具有重要的现实意义。