Control of propagation velocity of sub-picosecond electrical signals on the micro strip lines involving quantum wells

该项目的主要目的是控制亚皮秒电信号在包含半导体量子阱的微带线(MSL)上的传播速度，其中电子和空穴是通过例如光激励产生的。在器件制作和测量的同时，利用时域有限差分(FDTD)软件对电磁场进行了三维计算。主要研究结果如下：(1)研究发现，在本项目初期，半导体衬底上制作的MSL中观察到的电信号是仅通过在衬底表面形成的单根信号线传输的电信号。单金属线光波导在微波和光学两种情况下都有报道。在太赫兹频段，金属复电导率的实部和虚部具有相同水平的带状线，可以作为研究Infu…的良好系统。电磁波导上表面等离子激元的增多。我们还发现，如果在金属单线上覆盖均匀的介质膜，信号沿金属单线的衰减和色散甚至可以比传统的MSL更低。因此，我们可以期待单线波导在未来的应用。(2)我们成功地制作了基平面由光学透明导体ITO制成的MSL。在这种MSL中，可以光学访问信号线和地平面之间的区域。实验证实，光谱范围在1 THz以下的信号可以传输1 mm以上，具有良好的传输特性。在FDTD计算的基础上，我们还证明了使用ITO的Drude模型对于精确预测高于1 THz频率的传输特性是必要的。(3)实验验证了在使用聚合物介质的薄膜MSL中传输亚皮秒电信号是可能的。(4)建立了在上述MSL中嵌入半导体量子阱的方法。在测量中，没有观察到传输速度的控制，主要是由于电子和空穴的激发不足。然而，由于本工作建立的器件制作方法具有良好的通用性，我们可以期待在未来实现功能性MSL的进展。较少

The major aim of this project was the control of propagation velocity of sub-picosecond electrical signals on micro strip lines (MSLs) involving semiconductor quantum wells, where electrons and holes are generated by with, for example, optical excitation. Along with the fabrication of the devices and the measurements, three-dimensional calculations of the electromagnetic fields were performed by using finite-difference-time-domain (FDTD) software. The major results are as follows.(1)It was found that the electrical signals observed, at the beginning of this project, in the MSLs made on semiconductor substrates are those waveguided only by the single signal line formed on the substrate surface. The waveguiding by single metallic lines has been reported in microwave and optical regimes. The strip lines in THz-frequency regime, where the real and imaginary parts of the complex conductivity of metals have the values in the same level, can be a good system for the investigation on the influ … More ence of surface plasmons on the electromagnetic waveguides. We also found that the attenuation and the dispersion of the signals along the single metallic line can be even lower than the conventional MSLs, if the line is covered by a uniform dielectric films. Hence we can expect the application of single-line waveguides in the future.(2)We successfully fabricated the MSLs where the ground plane is made of an optically-transparent conductor, ITO. In such MSLs, optical access into the region between the signal line and the ground plane is possible. It was confirmed, experimentally, that the signals whose spectral range is below 1 THz can be transmitted for more than 1 mm with good propagation characteristics. We also showed that the use of Drude model for ITO is necessary for the precise prediction of the propagation characteristics in the frequency higher than 1 THz, on the basis of the FDTD calculation.(3)It was experimentally verified that the transmission of sub-picosecond electrical signals over a few mm is possible in the thin film MSLs in which the polymer dielectric is used.(4)Methods for embedding semiconductor quantum wells in the MSL described above were established. In the measurement, the control of the propagation velocity was not observed, mostly because of the insufficient excitation of electrons and holes. However, since the device fabrication method established in this work has a good versatility, we can expect the progress for realizing functional MSLs in future. Less