Electronic Structure Analysis and Control of Conductive Properties of Amorphous Chalcogenides

点击翻译按钮获取中文摘要

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.