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Surface doping of ZnO nanowires with Bi: Density-functional supercell calculations of defect energetics
摘要： Defect calculations using the density and hybrid functionals in combination with the supercell approach are employed to characterize the electrical properties of a number of ZnO nanowires of various thicknesses doped with Bi atoms occupying surface sites. The variation of the differences between the total energies of charged and neutral supercells with the supercell size is studied, which led the authors to devise an extrapolation procedure to obtain reliable defect energetics in the dilute defect limit. The calculated defect formation energies indicate that although the substitution of Bi into Zn or O sites can take place spontaneously under suitable thermodynamic conditions, the substitution into Zn sites is generally more likely. The defect (charge-state) transition energies are computed and parameterized as a function of the nanowire thickness. It is revealed that the substitution of Bi into O (Zn) sites on the surface of ZnO nanowires yields deep acceptor (shallow donor) levels (except for extremely thin nanowires). It is therefore concluded that the incorporation of Bi into the surface of ZnO nanowires results in n-type doping.
关键词： ZnO nanowires,defect energetics,n-type doping,bismuth doping,supercell calculations,density functional theory
更新于2025-09-23 15:23:52
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Impact of Bi doping on CdTe thin films: Thermal annealing evolution of physical properties for solar cell absorber layer applications
摘要： To mitigate probability of instability and device degradation associated with traditional Cu doping and to tune required band gap as well as to reduce open circuit voltage loss to solar cell device, a study on evolution to the physical properties of Bi-doped CdTe films is reported. Thin films of CdTe:Bi 2% alloy are developed employing electron-beam deposition followed by air annealing. Structural studies reveal that films have preferred crystal growth along (111) plane and with annealing, films turned out to be polycrystalline. Absorbance of films is found to be affected with annealing where 450 °C annealed films show maximum absorbance. The current-voltage measurements show linear relationship reveal to ohmic contacts between the films and transparent conducting oxide substrate and conductivity is observed to be varied with annealing. The atomic force microscopy study indicates an increase in surface roughness with annealing (except for 300 °C). Our findings warrant that the optimized physical properties of CdTe:Bi 2% films annealed at 450 °C may play important role to enhance the solar cell device performance concerned.
关键词： Bismuth doping,Absorber layer,Air-annealing,Thin films,Cadmium telluride,Electron beam evaporation
更新于2025-09-23 15:19:57