Effects Of Electrical And Optical Properties Of Doping And Vacancy Defects On SnO₂ And TiO₂

Transparent conductive oxide(TCO) materials have been widely used in optoelectronic devices owing to the unique properties of high transmittances in visible light and high electrical conductivity. Compared with Sn-doped In2O3, as a rutile tetragonal crystalline structure with a wide band gap(3.6eV) and high excitation binding energy(130e V) at room temperature, tin oxide is a potential TCO material. Moreover, For anatase TiO2, there is more prominent photocatalytic efficiency, and oxygen vacancy is easy to form under low temperature. Now, n-type SnO2 film has been prepared and utilized extensively in industry. However, p-type semiconductor has only a few reports regarding the film preparation because of the larger hole effective mass and the worse carrier mobility, their active functions based on p–n junction have not been practically applied. But p-type semiconductor is the important part of p–n junction. In this paper, the p-type SnO2 and S、Se、Te-doped SnO2 were calculated utilizing the first principles method. After Zn-doped TiO2, titanium vacancy, oxygen vacancy, S and N-doped TiO2 were also investigated.The electronic structures and optical properties of intrinsic SnO2, Zn-doped SnO2 and their vacancy deffects are explored by using first-principles calculations. Zn-doped SnO2 is a p-type semiconductor material, the reason is Fermi level shifts into the valence band, and the unoccupied states on the top of valence band come from Zn 3d and O 2p states. Sn vacancies increase the relative hole number of Zn-doped SnO2, which results in a possible increace of conductivity. The Zn-doped SnO2 shows distinct visible light absorption, this phenomenon can also be seen apparently when the Sn vacancies present in crystal, and the blue-shift of optical spectra can be observed. Moreover, independent bands are found in S、Se and Te-doped SnO2. The structural stability of S-doped SnO2 is the best among them, but the visible absorption of Te-doped SnO2 is the best though whose stability is the worst. We also can know that red- shift optical spectras are observed in three materials. Last, for TiO2、Zn-doped TiO2 and Zn-doped TiO2 with Ti vacancy are p-type semiconductor material with visible light absorption. Independent band is found at the bottom of the conduction band in Zn-doped TiO2 with oxygen vacancy. The structural stability of Zn-doped TiO2 with O vacancy is better between Zn-doped TiO2 with Ti vacancy and Zn-doped TiO2 with O vacancy. And there are independent bands at the top of valence band for Zn/S co-doping TiO2, so red-shift optical spectra can be observed, too. Zn/N co-doping TiO2 can improve optical catalytic property.