Grain Boundary Conduction Control in Polycrystalline Semiconductors

本课题研究了多晶半导体的导电性，重点研究了用化学气相沉积法在玻璃衬底上沉积的多晶氧化锡（SnO_2）薄膜的导电性。为此，我们建立了一个宽温区霍耳效应的计算机自动测量系统。该系统能在15 ~ 300 K温度范围内测量一系列SnO_2多晶薄膜的霍尔效应，并能自动分析SnO_2薄膜的载流子浓度和迁移率数据。结果，我们得到了以下结果：i）SnO_2薄膜中的F杂质存款在晶界处，减少载流子散射，从而降低了SnO_2薄膜的电阻率; ii）SnO_2薄膜中的电子迁移率是由F杂质的中性和电离散射决定的，这些杂质在这种多晶薄膜中局限于晶界处，（3）我们还尝试了掺杂其它杂质如3d过渡金属或稀土金属，以在低电阻率SnO_2薄膜中寻找新的杂质，但目前还没有找到有效的杂质。

In this research project, we have investigated the electrical conduction in polycrystalline semiconductors, with emphasis on the electrical conduction of polycrystalline tin oxide (SnO_2) thin films deposited on glass substrate by the chemical vopr deposition method. For the purpose we have constructed an automatic measurement system of Hall effect in a wide temperature range by using a computer. In this system we were able to measure Hall effect of a series of SnO_2 polycrystalline thin films in the temperature range from 15 K to 300 K, and also analyze automatically data of carrier concentration and mobility of SnO_2 films. As a result, we have obtained the following results: i) F impurities in SnO_2 films deposit at grain boundaries and reduce carrier scattering, resulting in the reduction of resistivity of SnO_2 films, ii) the mobility of electrons in SnO_2 films is determined by the scattering due to neutral and ionized impurities of F in SnO_2 which are locarized at the region of grain boundaries in this polycrybtalline semicondcutors, iii) we have also tried to dope other impurities such as 3d trandition metals or rare earth metals to find a new impurity in SnO_2 films with low resistivity, but at present could not find an effective impurity for the purpose.