Zero-field splitting parameters and local structures for tetragonal Cr²⁺ centers in Cr²⁺-doped ZnSe semiconductors

The inter-relation between zero-field splitting (ZFS) parameters and local lattice structures of the (CrSe₄)^6- clusters in ZnSe semiconductors has been established by using the complete diagonalization (of the energy matrix) method. On the basis of this, the local lattice distortions, the ZFS parameters D, a, F and the optical spectrum for Cr²⁺ ions doped into ZnSe are theoretically investigated, and the contributions of the spin singlets have been taken into account. The calculated ZFS parameters are in good agreement with the experimental values. From our calculations, the tetragonal distortion parameters ΔR = 0.091Å and Δθ = 4.28°of Cr²⁺ in ZnSe are acquired, and the results suggest that there exists a tetragonal expansion distortion for the local lattice structure of (CrSe₄)^6- clusters in ZnSe crystals. The influence of the spin singlets on ZFS parameters is also discussed, indicating that the contributions to ZFS parameters a and F cannot be ignored.