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Investigation of dynamical conductivity in quantum nanostructures by time-domain terahertz spectroscopy

通过时域太赫兹光谱研究量子纳米结构的动态电导率

基本信息

批准号：
15206037
负责人：
HIRAKAWA Kazuhiko
金额：
$ 24.54万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2005
项目状态：
已结题

项目摘要

In this research project, we investigated dynamical conductivities in quantum nanostructures by using terahertz (THz) radiation as a probe for ultrafast carrier motion. The main results are ;1.Carrier dynamics in semiconductor superlattices and THz gain of Bloch oscillating electrons : By analyzing the THz waveforms emitted from semiconductor superlattices pumped by femtosecond laser pulses, we have shown that Bloch oscillating electrons have dispersive THz gain for the first time. Furthermore, the dominant dephasing mechanism of Bloch oscillation has been identified to be interface roughness scattering.2.Non-equilibrium transport in ultrafast transistors: To understand the performance of ultrafast transistors, we have investigated the THz radiation from non-equilibrium transport in bulk GaAs. It is found that the initial acceleration of photoexcited electrons starts to decrease with increasing field above 50 kV/cm, suggesting the importance of band mixing effect. Furthermore, we proposed a novel method to characterize the cutoff frequencies of ultrafast transistors beyond the frequency region accessible by conventional network analyzers.3.Conduction dynamics of single molecule/dot junctions : We planned to investigate the conduction dynamics of nanojunctions in which single molecules or quantum dots are probed by nanogap electrodes. Although we could measure dc characteristics, THz dynamics could not be characterized mainly due to their stability problem. This sub-project is being continued in our new project "Physics and control of terahertz dynamics of quantum nanosystems" (Grant in Aid No.18201027).

在这个研究项目中，我们使用太赫兹（THz）辐射作为超快载流子运动的探针，研究了量子纳米结构中的动态电导率。主要结果有：1.半导体超晶格中的载流子动力学和布洛赫振荡电子的太赫兹增益：通过分析飞秒激光脉冲泵浦的半导体超晶格发射的太赫兹波形，我们首次证明了布洛赫振荡电子具有色散太赫兹增益。此外，布洛赫振荡的主要失相机制已被确定为界面粗糙度散射。2.超快晶体管中的非平衡输运：为了了解超快晶体管的性能，我们研究了块状砷化镓中非平衡输运的太赫兹辐射。研究发现，随着场强增加到50 kV/cm以上，光生电子的初始加速度开始减小，这表明能带混合效应的重要性。此外，我们提出了一种新方法来表征超快晶体管的截止频率，超出了传统网络分析仪可访问的频率范围。3.单分子/点结的传导动力学：我们计划研究纳米间隙电极探测单分子或量子点的纳米结的传导动力学。虽然我们可以测量直流特性，但太赫兹动力学无法表征，主要是由于其稳定性问题。该子项目正在我们的新项目“量子纳米系统太赫兹动力学的物理与控制”（援助编号：18201027）中继续进行。