Study Of Znte And Rare Earth Doped Znte On Electronic Structure And Electrical Properties

The band structure and the intensity of states of ZnTe and rare earth doped ZnTe were obtained using the plane wave ultra soft pseudo potential method based on density functional theory (DFT) and generalized gradient approximation (GGA) according to the generally used design of the low resistance Ohmic contact in CdS/CdTe solar cells, and we analyzed the electrical structure in the aspect of conductivity. Calculation result shows that Y or La doping makes the ZnTe electron effective mass decreases and Gd or Nd doping makes the ZnTe electron effective mass increases, and Gd, Y or La doping changed the ZnTe into a degenerate semiconductor, in which the carrier concentration has the similar orders of magnitude. The lattice constants of Gd, Y, La and Nd doped ZnTe were obtained after the geometry optimization and the lattice mismatch between ZnTe:R and ZnTe was calculated, which shows that the lattice constant increases after Gd, Y or La doping and the lattice constant decrease after Nd doping. The lattice mismatch of Gd, Y, La and Nd are13.5%,5.944%,23.4%and4.03%respectively, so the lattice mismatch degree between ZnTe and Nd-doped ZnTe is the lowest. We also find that ZnTe is a p-type semiconductor, which will be transformed into the n-type semiconductor in Gd-doped ZnTe, Y-doped ZnTe and La-doped ZnTe, and Nd-doped ZnTe is a strong p-type semiconductor.The ZnTe and Nd-doped ZnTe films are grown on the glass substrate by double source vacuum evaporation, and the annealing proceeded in150℃,175℃,200℃and225℃with Ar gas protection for30minutes. We analyzed the electrical properties of the films by XPS test and Hall system test. Test result shows that the chemical shift of Zn decreases because of Nd doping, which can promote the combination of Zn and Te. The Nd-doped ZnTe film conductivity type is p-type, of which the bulk carrier concentration will decrease and the mobility will increase as the rising of annealing temperature. The conductive performance has been greatly improved because of the Nd doping.