The Study Of Preparation And Optical Properties On N Doped Cu₂O Films

Cu2O is a p-type direct band-gap semiconductor (Eg～2.1eV) with cuprite structure of space group Pn3m and its lattice parameter is 0.4296 nm. Cu2O has been regarded as one of the most promising materials for application in photovoltaic cells because of its high absorption coefficient, non-toxicity and low cost producibility. Recently, It has received more attention for doping to improve the electronic and optical properties.In this thesis, we use CuO for sputtering target by radio-frequency magnetron sputtering method. We study the behavior and optical properties for nitrogen doping and N-doped Cu2O films at different deposition temperatures, and calculate the electronic structure of Cu2O and N-doped Cu2O cells with first principle. The results are summarized as follow:1. The flux of nitrogen has important influence to generate the pure Cu2O films under the doping to the Cu2O films. The films of small nitrogen flux are highly Cu2O (100) textured. With the increase of nitrogen flux, the film transfers to be Cu3N phase that will reduce the transmittance of films.2.It is found that the Cu2O samples are highly (100) textured at the low deposition temperatures, and gradually change to be highly (111) textured at the deposition temperature of 500℃.With increasing the deposition temperature, the increase of free energy of critical nucleation is suggested to dominate the change of film texture. The surface morphologies of the films have the spatial scaling exponents greater than 1,indicating that the film growth can be attributed to the surface-diffusion-dominated growth. The bandgap energies of N-doped Cu2O films deposited at different temperatures are determined to be 2.52±0.03 eV.3. It is found that the N-doped Cu2O films are changed to be a direct allowed band-gap semiconductor and the optical band gap energy is enlarged. The first-principles calculations indicate that band gap energy enlarged relates to the top of valance band and the bottom of conduction band. The change, from a direct forbidden band-gap transition to a direct allowed band-gap transition, can be attributed to the occupation of 2p electrons of N at the top of valence band in the N-doped Cu2O films.