XAFS investigation of the local structure of cadmium in Cu(In[subscript 0.7]Ga[subscript 0.3])Se₂-based thin films

Graduation date: 2004We have performed fluorescence extended X-ray absorption fine structure\ud (EXAFS) measurements on the Cd K-edge of partial electrolyte (PE) treated\ud Cu(In[subscript 0.7]Ga[subscript 0.3])Se₂ (CIGS) thin film samples using synchrotron X-ray radiation. This data was compared to the EXAFS spectra of CdSe and CdO standards. Cd local structure\ud models were constructed and used for the least square analysis of the spectra. The first\ud model employed implantation of a cadmium atom and a single oxygen atom into the\ud CIGS lattice. Specifically, an oxygen atom was introduced in the tetrahedral bonded Cd-Se local structure. Employing FEFF8 with WinXAS software package, experimental data\ud was theoretically fitted to the first shell single-scattering paths of the Cd atom in the (PE)\ud treated Cu(In[subscript 0.7]Ga[subscript 0.3])Se₂ thin film samples. The main peak observed in the data represents the Cd-Se bonds and the shoulder corresponds to the Cd-O bond. However, the number of\ud total nearest neighbors is not consistent with this model. A two-phase model that includes\ud both Cd-Se tetrahedron and Cd-O octahedron were then reconstructed. Again, a least-agrees very well with the experimental data, and the total first nearest neighbor number is\ud consistent with the two phase model at NN=4.2. This study indicates the surface of Cd\ud partial electrolyte treated Cu(In[subscript 0.7]Ga[subscript 0.3])Se₂ thin films contains both CdSe and CdO