First-principles Calculation Of N,Hf Sigle-doped And Co-doped ZnO

With the development of optoelectronic information technology and computer over these years, as a new type of wide band direct transition type semiconductor oxide material after GaN, comparing with other optoelectronic material, ZnO has the excellent properties of piezoelectric, photoelectric, dilute magnetic characteristics, non-toxic, low cost, high radiation resistance, and strong chemical stability. Because of these advantages, ZnO has more extensive research and good application prospects in solar cell, pressure sensitive device, thermal sensor, liquid crystal display, and UV detector, and so on.Therefore, in this paper, we studied Hf and N doped ZnO materials by by the CASTEP software package based upon the density function theory(DFT). The main research contents and results are as follows:Firstly, we calculated and analysed the properties of the crystal structure, the electronic structure, Mulliken Charge population and optical properties in pure ZnO system. The results show that the pure ZnO system is a direct transition band structure with a gap width of 0.733 eV, the conduction band is mainly contributed to by the 4s, 3p states of zinc, and a few by the 2p states of O; the band near the Fermi level is mainly contributed to by the O 2p states; in optical properties aspects, its dielectric function real part value is 6.02; the imaginary part has three obvious peak when the energy of photoelectrons are respectively equal to 1.27 eV, 6.53 eV, and 10.16 eV; the scope of the absorption of energy the absorption peak is wide, and it is mainly in the range of 4.7~27.6 eV. When the energy is 17.18 eV, it has reached maximum peak level 3.09×105 cm-1; the reflection spectrum peak is about 15 eV, the static refractive index is about 2.45, and the energy loss peak is near 19.6 eV.Secondly, we calculated and analysed the properties of Zn1-xHfxO system(x=3.12, 4.17, 6.25, 12.5). With the increase of mol percentage of Hf doping, the volume expanded, Fermi level goes into the conduction band, its nearby partion is mainly contributed to by the 5d states of doped atom Hf, and ionic bonding component of Hf-O is prominent, so it is more possible to form n type ZnO material due to Hf doped. By comparing with the absorption, reflection and refraction, we find that adding Hf atoms moderately may increase transmittance in the high energy region of ZnO system, in which the loss function appears red shift. All these properties are similar to the experimental results of Hf doping, thus we know that proper amount of doped ZnO system of Hf is expected to play a role in preparation of optoelectronic devices and other fields.Then we calculated and analysed in Zn16O15 N system. The calculation results show that, the cell volume of doping system was expansion, the absorption peak, reflection peak, and energy loss spectrum peak moved towards the direction of low energy, and showed the red shift phenomenon. Further more, the Fermi level Ef moved to the valence band ang formed degenerated state, which made the top of valence band appeared the superfluous carrier hole around ZnO, so near the Fermi level form the acceptor level, which is beneficial to the formation of P type Zn O system.Finally, the properties of the crystal structure, electronic structure, mulliken Charge population and optical properties of the system of Hf and N co-doped Zn O(Zn15O16-xHfNx, x=1,2,3,4) are calculated by the first-principles based upon the density function theory(DFT). We get some computational conclusions, such as the sizes of co-doped systems unit cell volume are bigger than undoped one’s; when the x is equal to 1, the Femi energy level of the system moves up, and moves through the conduction band, all this demonstrates the matter is n-type semiconductor, and the Redshifts of absorption peak and reflection peak of the system are less; when the x is equal to 2, 3, or 4, the Femi energy levels of the co-doped system Zn15O16-xHfNx are a little lower than valence-band maximum, with the doping ratio increasing, the depth of the Femi energy level under valence-band maximum is gradually increasing, the contribution of 2p state of N element is more and more outstanding, which indicates the matter is p-type semiconductor, and its Redshifts of absorption peak and reflection peak are big. As a result, all the properties widen the application of co-doped ZnO in visible light field.