First-principle Study On The Modification Properties Of Doped SnO₂Semiconductors

SnO₂is one kind of semiconductor materials that has the wide band gaps and that has thestructure of rutile type, which is one of the important function materials of inorganic. SnO₂isa promising transparent conductive material with3.6eV direct band gap and130meV excitonbinding energy. Research shows that doped Sn02has various special properties, such as highconductivity, high transmission rate, high infrared reflectance and ultraviolet absorption rate,thereby Sn02has a broad application prospect. In our paper, we calculate SnO₂basedsemiconductor, which use the full-potential linearized augmented plane wave method（FP-LAPW） based on the first-principles of density functional theory （DFT） within thegeneralized gradient approximation （GGA） for the correlation and exchange effects in ourframework.First, we construct a222SnO₂supercell, and investigate the electronic and opticalproperties of Sn1-xMxO2（M=Fe, Mn; x=0,0.0625,0.125,0.1875,0.25）, Fe-S co-doped SnO₂,and electron-injected Sn₁₅FeO₃₂. The calculation indicates that the Fe doped materials showhalf-metallic property. With increasing of Fe-doping concentration, the Fermi level goes intovalence band gradually, and the band gap reduces with the enhancing coupling of Fe atoms.Moreover, impurity can change the property of the bond formation to some extent, and makeit have metallic bond character. Furthermore, we find that the optical spectra （such asabsorption spectrum, extinction coefficient, etc） shift blue corresponding to the imaginary partof dielectric function. Meanwhile, the doped Mn reduces the band gap which can be attributedto a series of impurity bands at the bottom of the conduction band caused by the stronghybridization between Mn3d and O2p. The material tends to become P-type semiconductorgradually. With the increase of Mn atom, both the imaginary part of dielectric function and theabsorption spectrum show red shift corresponding to the change of band gap. The research ofFe-S co-doped SnO₂show that the two co-doped compounds are all direct transitionsemiconductors with half-metallic properties. The DOS move to the low energy with theincrease of S concentration. The charge density of co-doped system redistributes, and thedegree of Fe polarization and the capacity of bonding enhance with the increase of S. What’smore, the peaks of imaginary part of dielectric function and optical absorption shift red and the absorption edge decreases with the increase of S concentration. Sn₁₅FeO₃₂withelectron-injection. When the concentration of injected electron is less than1.2, the materialshows a half-metallic behavior. When the concentration is greater than1.2, the material showsa metallic behavior. When the electron concentration is1.0, the total magnetic moment is5.19μB, which is the maximum. For the optical properties, such as the imaginary part ofdielectric function, reflection and absorption, the peaks changed greatly at low energy andform blue shift, and the optical absorption edge increases, which are correspond to the changeof the band gaps.Secondly, we construct a2×2×3SnO₂superlattice, and investigate the electronicstructures and optical properties of Fe, Mn （one and two layers） doped SnO₂superlattice andFe-Mn codoped SnO₂superlattice. We find that when doped Fe of one and two layers, thereexists strong hybridization between Mn3d and O2p, and causes a series of impurity bands atFermi level. The electrical conductivity of the material enhanced, the absorption spectrabroadened, and the reflective and refractive index increased in the UV-visible regin. Whendoped Mn of one layer, there exist spin up occupied states at Fermi level, the material showshalf-metallic properties. When doped Mn of two layers, there exist big differences betweenthe two layers of atoms, but the magnetic moments of impurity atoms increased. For theFe-Mn codoped SnO₂superlattice, there exist big difference between co-dope and single-dope,especially the partial density of Fe, Mn atoms. The optical spectra move towards low energylevel and the curve is smoother compared with the single-dope.Finally, SnO₂is similar to graphene in the stable structure of honeycomb when optimized.We also make efforts to construct the model of the SnO₂nano-surface, and have some success.Calculated results show that the density states of surface structure is broadly consistent withthe original cell of SnO₂, but the energy splitting increased. The coefficient of optical spectradecreased, the curve is smoother. The refractive index increased in UV-visible.