Investigation of Photo-Response in Micro-structure Device of Photo-conducting Semiconductor and Superconductor

为了研究光照对超导体与光导半导体之间超导邻近效应的影响，我们在掺杂铟的Pb_<1-x>Sn_xTe （x=0.25）半导体单晶上制备了一对Pb、In、Au多层超导薄膜的介观器件。在掺铟的Pb_<1-x>Sn_xTe中，电子迁移率非常高，持续光电导率也很大，这表明超导在半导体中的穿透长度很长，变化范围很广。我们测量了这些器件在光照下的超导特性。在超导体膜间隙宽度小于0.2 ~ 0.3mum的器件中，电流-电压曲线在4.2K处出现滞回，这是典型的约瑟夫森结特性。此外，临界电流（电阻的突然增加点）随着光照的增加而增加。根据这些结果，我们成功地通过照明改变了介观器件的超导特性。使用由该基金购买的交流电阻桥，我们还测量了量子霍尔体系中二维电子系统（GaAs/AlGaAs异质结构）中电容的磁场依赖性。研究发现，霍尔高原处的电容底值不是由栅极面积决定的，而是由栅极边缘长度决定的。这些结果不能用传统的磁电容解释来解释，其中电容与二维电子气体的态密度直接相关。我们提出了一个底部值由边缘状态的面积决定的模型。利用该模型估计了边缘状态的宽度，并与现有的理论进行了比较。

In order to investigate the influence of illumination on the superconductivity proximity effect between superconductor and photo-conducting semiconductor, we have made the mesoscopic devices from a pair of Pb, In, Au multi-layr superconducting films on indium doped Pb_<1-x>Sn_xTe (x=0.25) semiconductor single crystal. The electron mobility is very high and the amount of persistent photoconductivity is large in indium doped Pb_<1-x>Sn_xTe, which indicates that the penetration length of superconductivity into semiconductor is long and could be varied widely. We measured the superconducting characteristic of these devices under illumination. In the devices with the gap width between the superconductor films below 0.2-0.3mum, the hysteresis in the current-voltage curve is observed at 4.2K, which is a typical characteristic of Josephson junction. Further the critical current (the sudden increase point of resistance) increases with increaseing illumination. From these results, we succeed in changing the superconducting characteristic of the mesoscopic device by illumination.Using an AC resistance bridge, which was purchased by this grant, we have also measured magnetic field dependence of capacitance in a two dimensional electron system (GaAs/AlGaAs heterostructure) in the quantum Hall regime. It has been found that the bottom values of capacitance at the Hall plateaus are determined not by the gate area but by the edge length of the gate. These results can not be explained by the conventional interpretation of magnetocapacitance, where the capacitance is directly related to the density of states of a two dimensional electron gas. We suggest a model that the bottom values are determined by the area of edge states. From this model, the widths of edge states were estimated and compared with the recent theory.