Correlation between the electronic structures and diffusion paths of interstitial defects in semiconductors: The case of CdTe

Using first-principles calculations, we study the diffusions of interstitial defects Cd, Cu, Te, and Cl in CdTe. We find that the diffusion behavior is strongly correlated with the electronic structure of the interstitial diffuser. For Cd and Cu, because the defect state is the nondegenerated s-like state under the Td symmetry, the diffusions are almost along the 111 directions between the tetrahedral sites, although the diffusion of Cu shows some deviation due to the coupling between the Cu d and host s orbitals. The diffusions of the neutral and charged Cd and Cu follow similar paths. However, for Te and Cl atoms, because the defect state is the degenerated p-like state under the Td symmetry, large distortions occur. Therefore the diffusion paths are very different from those of the interstitial Cd and Cu atoms, and depend strongly on the charge states of the interstitial atoms. For Te, we find that the distortion is mostly stabilized by the crystal-field splitting, but for Cl, the exchange splitting plays a more important role.