EXPERIMENTAL STUDY ON NUMBER DENSITY AND MOBILITY OF ELECTRIC CARRIER IN A CERAMIC INSULATOR,ALUMINA

已经尝试测量陶瓷绝缘体氧化铝中的载流子的数密度和迁移率。所使用的样品是高纯氧化铝多晶和高纯单晶蓝宝石。电子被认为是氧化铝和蓝宝石的导电性的原因。然而，这些材料的电导率很低，在中等温度下为10^&lt；-13；Sm^&lt；-1&gt；因此，通常情况下，测量电导率以及载流子的数密度和迁移率是非常困难的。在本实验中，我们试图利用所谓的辐射诱导导电性(RIC)现象来增加电导率，从而增加载流子的数密度。RIC是一种类似于半导体中的光电导现象。一般来说，测量辐射环境中的电导率是非常困难的，但通过改进一种技术，在本实验研究中可以可靠地测量辐射环境中的电导率。利用这一技术，我们得到了电导率与晶体取向、晶体微结构等有关的数据。此外，我们还观察到了绝缘体在辐照下的一些非欧姆行为。这种非欧姆行为可能是由电极和绝缘体之间的边界附近或晶界处的载流子充电引起的。此外，一些电荷陷阱效应在某些点上可能是电子杂质造成的。所获得的数据将为我们提供有关氧化铝和蓝宝石中载流子的数密度和迁移率的定量信息。

It has been attempted to measure a number density and a mobility of an electric carrier in a ceramic insulator, alumina. The specimens used are highly pure alumina polycrystals and a highly pure single crystal sapphire. Electrons are thought to be responsible for the electric conductivity in alumina and sapphire. However, the electrical conductivity in these materials are very low, namely in the order of 10^<-13>Sm^<-1>, at moderate temperatures. Thus, the measurements of the electrical conductivity as well as the number density and the mobility of the electric carrier is very difficult in general. In this experiment, we tried to use the phenomenon so-called radiation induced condutivity (RIC) to increase the electrical conductivity, thus, increasing the number density of the carrier. The RIC is the phenomenon similar to the phtoconductivity in semiconductors. It is in general very difficult to measure the electrical conductivity in radiation environments, but by refining a techniques it became possible to measure the electrical conductivity reliable in the radiation environments in this experimental study. The developed technique made it possible to measure the electrical conductivity in the range of to 10^<-11>-10^<-4>S.Using this technique, we obtained the data concerning dependence of the electrical conductivity on the crystal orientation, microstructures of the crystals, and so on. Also, we observed some non-ohmic behavior in insulators under irradiation. This non-ohmic behavior may be caused by the charge-ups of electric carriers near the boundaries between the electrodes and the insulators or at grain boundaries. Also, some charge trap effects at some point electrical impurities may be responsible. The obtained data will give us the quantitative information concerning the number density and the mobility of the electrical carrier in alumina and sapphire.