Electronic Structure Analysis and Control of Conductive Properties of Amorphous Chalcogenides

用同步轨道辐射作为激发光，用紫外光电子能谱法研究了a-In_2Se_3的电子结构。发现a-In_<>Se_3与结晶In_2Se_3具有几乎相同的价带结构。价带由Se 4p非键带、Se 4p- in 5p - p-p sigma键带、Se 4p- in 5s p-s sigma键带和Se 4s核心键带组成。在a- in_2se_3的光导激发谱中，除了在与带隙相当的波长处有一个大峰外，在0.7eV处有一个小峰。这些观测结果支持了基于紧密结合能带的模型，即四面体配位的In和Se产生了上述价带结构，而作为次要成分的八面体配位的In原子在四面体配位的原子带隙中形成了假导带。在a- in_2se_3中发现了假导带作为导带。这导致在非晶硫族化合物中观察到异常低的电传导活化能。在上述实验中，我们很好地证实了电子在主要由p位阳离子的ns原子轨道构成的导带中的高迁移率。在高迁移率对高磁化率有效的工作假设下，用三次谐波产生法估计了a- sno_2和a- in_2o_3的三阶非线性磁化率。a-SnO_2和a-In_2O_2的磁化率分别为5X10^<-12> esu和1X10^<-12> esu。工作假设对于寻找高磁化率的新材料是有效的。

Electronic Structure of a-In_2Se_3 was examined by ultraviolet photoelectron spectroscopy with syncrotron orbil radiation as an excitation light. It was found that a-In_<>Se_3 has almost identical valence band structure with crystalline In_2Se_3. The valence band is composed of Se 4p nonbonding band, Se 4p-In 5p p-p sigma bonding band, Se 4p-In 5s p-s sigma bonding band and Se 4s core band from the top. In the excitation spectrum of photoconduction in a-In_2Se_3 a small peak was observed at about 0.7eV in addition to the large peak at a wavelength equivalent to the band gap. These observations support the model proposed on the basis of tight binding energy band that tetrahedrally coordinated In and Se produce the above mentioned valence band structure and octahedrally coordinated In atoms, which are a minor component, constitute a pseudoconduction band in the band gap of the tetrahedrally coordinated in atoms. The pseudoconduction band was found to act as a conduction band in a-In_2Se_3. This results in the anomalous low activation energy for electrical conduction observed for the amorphous chalcogenides.A large mobility of an electron in the conduction band mostly constructed by ns atomic orbitals of p-block cations is well established in the above mentioned experiments. The third order nonlinear susceptibility of a-SnO_2 and a-In_2O_3 was estimated by the third harmonic generation method under a working hypothesis that the high mobility is effective for the high susceptibility. The susceptibility values of 5X10^<-12> esu and 1X10^<-12> esu were found for a-SnO_2 and a-In_2O_2, respectively. The working hypothesis was found to be effective in searching a new material with the high susceptibility.