DFT Calculation For The Lattice And Optical Properties Of Doped CdTe And ZnO

The lattices and electronic properties of CdTe,CdSbxTe1-x and MxZnyOz (M=Na,Li,N,Mg,Na-Mg,Li-Mg,Li-N) are optimized and calculated using ultra-soft pseudo-potential approach of the plane wave based upon DFT of first-principle. The electronic bands, density of states and optical properties are obtained accordingly, and the doping-effects on the electrical and optical properties also are analysed.The electronic bands, density of states, absorption spectra, the energies of valence band maximum (VBM), the conduction band mininium (CBM) and the energy gap Eg with different doping concentration x of Sb are calculated. It is indicated that, due to the CBM ascended, the hole concentration of the system increased, the interaction between atoms weaken and the binding energy decreased, the energy gap increases with the increased Sb-doping. With the increasing of x, the solar energy absorbed by the system increases as x≤0.125, decreases as 0.125＜x＜0.25 and increases again as x＞0.25. It was pointed out that a large proportion of Sb substituting for Te CdTe, which could be proparede with the traction effect of substrate surface to the lattice, would improve the optical performance.Electronic bands, density of states, and absorption spectra of MxZnyOz are calculated and analyzed. The results shows that:(1) The band gap of ZnO lattice becomes widen as the substituting Na atom for Zn atom, because of bond states in the valence bands and an antibond states in the conduction bands. The energies of the valence bands and the number of holes would increase by the reduction of the valent electrons. And the number of holes spin up was more than holes spin down.The Mg atoms induce higher energies of the conduction bands because their 3p orbital would increase the energy gap of the lattice. (2) The substituting N atomes make the convergent bands split and the number of holes near the Fermi surface from other atoms icrease. Some acceptors are produced with a high energy level. The convergent splits are strenghthen and the energy of the acceptors becomes lower with the Mg-N codoping in ZnO lattice, which is prefered to the p-type conductivity with low resistance. (3) The order of the solar energy absorption capacity is shown as follows: Zn0.75Mg0.125Li0.125O＞Zn0.875Li0.125O＞Zn0.75Mg0.125Na0.125O＞Zn0.875Na0.125O＞Zn0.875Mg0.125N0.125O0.875＞ZnN0.125O0.875＞Zn0.875Li0.125N0.125O0.875.