Studies On The Electronic Properties Of Spinel Type Complex Metal Oxide

With the rapid development of electronic information technologies, people are demanding for higher and higher visual quality, therefore, a large number of new display technologies emerge endlessly. Thin-film transistor, as a kernel component in active matrix drived circuits in current mainstream display technologies, is a key element to boost display technology for further development. Recently, amorphous oxide semiconductor thin film transistor(AOS-TFT) have been widely recognized as the most promising and next generation TFT technology contributing to its excellent performance, such as high mobility, transparent in the visible region, great stability, low temperature preparation and so on. However, up to present, the conductive mechanism of amorphous oxide semiconductor materials remains controversial and requires further study. Therefore, in this thesis, using the first principle calculation method based on density functional theory, a theoretical research on the electronic properties of Mg Sn Al O(MTAO)-type complex metal oxide semiconductor material has been proposed for the first time. The main works as well as obtained results of this thesis are summarized as follow:1. With the first principle calculation method based on density functional theory, the geometry structure and electronic structure(including band structure, density of states, Milliken population analysis and electron density difference) of eigenstate Mg Al2O4 and Mg2 Sn O4 with normal spinel structure have been studied. Meanwhile, by being compared with other studies, the results obtained from this thesis are verified to be reliable.2. The geometry structure and electronic structure of MTAO system with different concentrations of Sn doped Mg Al2O4 have been studied. The results indicate that with the increase of the doping concentration, the effect of Sn on the performance of the system is gradually strengthened. No matter which site Sn substitutes, the crystal lattice constant increases but the whole structure remains spinel. Besides, the overall band structure and density of states of Sn doped Mg Al2O4 system move toward lower energy states. Meanwhile, a donor impurity level consisting of Sn-5s state is induced in the middle of its band gap, which is a deep level, acting as a center of recombination of electron-hole pairs. In addition, when Sn is doped into Mg Al2O4 as a substitutional impurity, the electronic localization in its conduction band decrease while the electronic effective mass in the bottom of the conduction band increase. Therefore, the MTAO system with Sn doped Mg Al2O4 still maintains a good insulating performance. In other words, Mg Al2O4 is insusceptible to Sn impurities, indicating that it is a promising insulator for MTAO-TFT.3. The geometry structure and electronic structure of MTAO system with different concentrations of Al doped Mg2 Sn O4 have been studied. The results shown that the substitution of Al impurity in Mg2 Sn O4 decreases the crystal lattice constant but the whole structure remains spinel. In the Al Sn structure, the overall band structure and density of states have a slight decrease relative to fermi level while the band gap increase slightly, but with the increase of Al doping concentration, the top of the valence band is gradually close to the fermi level. What is more, when Sn is substituted by Al, the electronic localization in both valence and conduction band decrease and Al-O form strong covalent bond, which are favorable for transferring electrons. In the Al Mg structure, the overall band structure and density of states move toward lower energy states accompanied by the fermi level into the conduction band, exhibiting typical n-type conductivity. Moreover, with the Al-3p state, the electronic localization in its conduction band is weakened, leading to the formation of conductive channels. All in all, the MTAO system with Al doped Mg2 Sn O4, expected to have good conductive properties, can be considered as the active layer of MTAO-TFT.