Electronegativity And Optoelectronic Properties Of Oxide Materials

Oxide semiconductors have many important applications in the field of ferroelectric, piezoelectric, sensors, solar cells, etc, which are closely related to the optoelectronic properties of materials. As one of the most important parameters to characterize the value of semiconductor application, band gap is the energy difference between the valence band maximum and conduction band minimum. All the materials are formed by the link of composition atoms with chemical bond, the properties of chemical bond can be used to reflect the physical or chemical properties of materials, and furthermore these physical or chemical properties can be expressed by the chemical parameters, such as the electronegativity. Electronegativity is such a kind of property which reflects the ability of an atom or a group to attract electrons, and it has been successful applied to many researches of material properties and material design after80years development.In this work, from the view of chemical bond theory, we analyzed the microstructure of oxides and established the relationship between band gap values and electronegativity. From the simple ANB8-N binary compounds, we found the basic factors that can influence the semiconductor band gap and investigated how they work:with the bond length and electronegativity we get the ability of bonded atoms to attractive valence electrons, and the larger attraction of the bonded atoms could enlarge the band gap; the effective covalency corrected by the radius ratio can reflect the effect of electron delocalization to a certain extent, and the effective covalency will decrease the band gap. Finally we got a band gap calculation formula for MO type oxides. Based on the viewpoint of chemical bond, we also analyzed the band gap of charge-transfer oxides, and established a quantitative relationship between band gap of these oxides and chemical bond parameters, such as electronegativity. The results of our calculation formula agreed with the experimental data well, and the excellent agreement gave us another example of applications of electronegativity in the band gap study of oxides.The study of impurity level is one of the most basic and important area in semiconductor researches. On the basis of the discussion of semiconductor band gap made by us in this work, we expanded the idea to the study of impurity level created in TiO2, which come from the study of band gap from the viewpoint of chemical bond. With electronegativity and other chemical parameters. we established a formula for impurity level calculation:the degree whether an electron can be excited was expressed by the valence electron density and bond strength that denoted by electronegativity and doping bond length. When the bond strength is large and the valence electron density is small, it is hard to excite the electron and the impurity level get close to the top of valence band. The calculated results agree well with the experimental data. The impurity level calculation formula which established based on electronegativity can be used to provide theoretical guidance in the search of proper impurity atoms for semiconductor doping.