First-Principle Study On The Electronic Structure And Material Properties Of SnO₂Semiconductor Superlattice

SnO₂as a new oxide semiconductor, with the wider band gap and large exciton bindingenergy are widely attention by many people. But the SnO₂-based semiconductors become thehot spot, because it generally has excellent light, magnetic and electric properties. So it willbe a very potential new material in the next generation. In this paper, by using thefull-potential linearized augmented plane-wave method （FP-LAPW） based on thefirst-principles of density function theory （DFT）, we have performed the whole work ofcalculating superlattice structure based SnO₂, within the generalized gradient approximation（GGA） for the exchange and correlation effects in the framework.Firstly, we calculate the electronic structure, band structure, complex dielectric function,absorption, reflectivity and refraction of Cr （one layer） doped SnO₂superlattice. It show thatwith the doping of Cr SnO₂superlattice forms new electronic occupied state near Fermi energywhich is contributed by Cr-3d and O-2p, Sn-5s. Dielectric spectrum appears three newdielectric peaks between0eV to5.0eV. In high-energy area, the position of main peak isbasically consistent with the pure SnO₂, but the intension reduced. Absorption spectrum,reflectivity spectrum and refraction spectrum also appear corresponding peak, which are causedby d-d transition of Cr atom.Secondly, we calculate the electronic structure, band structure and optic properties of Cr（n layers, n=1,2,3） doped SnO₂superlattice. The result show that these several doping are allhalf-metallic. The magnetic moment and electroconductivity will be enhanced with the increaseof n. The magnetic moment is contributed mainly by Cr-3d states and minority by O-2p states.Due to p-d hybridization, the doping-Cr makes the DOS of oxygen producing spin polarization.Because of the d-d transition of Cr atom, in0¹.8eV, the position of first absorption peak willmove back with the increase of n. In1.8eV⁷.0eV, the magnitude of the peak formed by p-dtransition is augmented with the increase of n. In7.0eV¹7eV, the magnitude of the peakformed by p-s transition is reductive with the increase of n.Thirdly, we calculate the influence of oxygen vacancy on electronic and magneticproperties in Cr （one layer） doped SnO₂superlattice. It is show that the magnetic moment ofthe system is7.98μBin Cr-doped SnO₂, and for per Cr atom is about2.00μB. If we introduce O vacancy in Cr-doped SnO₂near Cr layer, the magnetic moment of each Cr atom is changed （oneis0.40μB, the other three atoms are about2.20μB）, while the total magnetic moment of thesystem is almost invariable. Differently, if the O vacancy is introduced in Cr-doped SnO₂faraway from Cr layer, the total magnetic moment of the system becomes to-2.02μB, and themagnetic moments of four Cr atoms are also changed to0.08μB,2.25μB,0.05μB,0.02μB,respectively.Fourthly, we select Co and Mn which have the similar electronic structure with Cr todoped SnO₂superlattice, and analyze the result. We find that the material illustrate metallicitythrough doping. The spin polarizability is not100%. Co-3d states、Mn-3d states and O-2pstates generate a strong hybridization. And it makes the magnetic moment of Co and Mnlower3.0μB, the other is contributed by oxygen. In lower-energy area, the dielectric spectrumis changed due to d-d hybridization between Co and Mn. Absorption spectrum and reflectivityspectrum also have corresponding change.Finally, we use the method of GGA+U to hand correlation energy, and recalculate thestructure of Cr （one layer） doped SnO₂superlattice. The result show that it forms manyimpurity peaks near Fermi energy by introducing U in Cr-3d orbit. But the material is stillhalf-metal. In valence band, the change of states makes the total magnetic moment changedfrom7.98μBto2.02μB. The magnetic moment of each Cr atom have also changed. Becausethe new impurity states, dielectric spectrum have a red-shift in lower energy area, and formstwo new dielectric peaks. The changes of absorption spectrum are consistent with dielectricspectrum.