Ultrafast carrier dynamics in the 10fs-time range probed by time-domain terahertz emission spectroscopy

在截止频率高于500 GHz的超快晶体管中，预计载流子将以非常不稳定的方式在沟道中行进。因此，理解高电场下载流子的非平衡输运是非常必要的。本研究的目的是进行定量比较的非平衡输运数据的时域太赫兹光谱和系综蒙特卡罗（EMC）的结果和提取本征载流子输运特性。实验结果表明，有限的样品厚度对实验结果有很大的影响。当加速场大于20 kV/cm时，空穴对THz信号的贡献变得显著.当考虑样品的几何形状和光激发条件时，THz数据与EMC计算结果吻合较好。此外，我们还研究了量子异质结构中的量子力学输运。 ...更多信息 自江崎和大津首次提出布洛赫振荡器以来，人们从实验和理论两方面对布洛赫振荡进行了大量的研究，并获得了太赫兹辐射。然而，从提出到现在已经过去了30年，太赫兹布洛赫振荡器还没有被实现。因此，建立对太赫兹区电子动力学运动的理解是至关重要<0.3>的<0.7>。为了确定SL微带中的高频电子电导率，我们提出了一种全新的方法，注意到时域太赫兹光谱固有地测量电子系统对外加偏置电场的阶跃响应，并且太赫兹发射的傅立叶光谱与高频电子电导率密切相关。发射的太赫兹电磁波的傅立叶谱与预测的电导率谱进行了比较。理论和实验之间的良好一致性强烈表明，由于布洛赫振荡电子的太赫兹增益至少持续到1.7THz。少

In ultrafast transistors with cutoff frequencies higher than 500 GHz, carriers are expected to travel in the channel in a very nonstationary manner. It is, therefore, essential to understand nonequilibrium transport of carriers subjected to high electric fields. The aim of this study was to make a quantitative comparison between the nonequilibrium transport data obtained by the time-domain THz spectroscopy and ensemble Monte Carlo (EMC) results and extract intrinsic carrier transport properties. It is found that the experimental results are strongly affected by finite sample thickness. Furthermore, the contribution of holes to the THz signal is found to become significant when the acceleration field is greater than 20 kV/cm. When the sample geometries and the photoexcitation conditions were property taken into account, the agreement between the THz data and the EMC calculations was good.Furthermore, we have also investigated the quantum mechanical transport in quantum heterostructures. … More Since the first proposal of Bloch oscillators by Esaki and Tsu, considerable effort from both experiments and theories has been made to search for Bloch oscillations and obtain terahertz (THz) emission. Even after three decades from the proposal, however, THz Bloch oscillators have not been realized yet It is, therefore, of prime importance to establish an understanding of the dynamical electron motion in the THz regime.In this work, we obtained a strong experimental support for the THz gain due to Bloch oscillating electrons in wide miniband GaAs/Al_<0.3>Ga_<0.7>/As SLs. For determining the high-frequency electron conductivity in SL minibands, we proposed a totally new approach, by noting that the time-domain THz spectroscopy inherently measures the step-response of the electron system to the applied bias electric field and that the Fourier spectra of the THz emission is closely related with the high-frequency electron conductivity. The Fourier spectra of the emitted THz electromagnetic wave were compared with the predicted conductivity spectra. The excellent agreement between theory and experiment strongly suggests that the THz gain due to Bloch oscillating electrons persists at least up to 1.7THz. Less