The effect of electron-phonon interaction in iron-doped III-V cubic semiconductors

A theoretical study of optical absorption and emission measurements of Fe2+ as a substitutional impurity in InP and GaP is presented. A new interpretation of the low-temperature absorption spectrum is proposed based on a weak Jahn-Teller interaction between the electronic excited states and a local gap mode of Gamma(5) symmetry. The model also includes the crystal potential, hybridization with the orbitals of the ligands of the host crystal, spin-orbit interaction and a weak dynamic Jahn-Teller coupling of the orbital ground state of Fe2+ with transverse acoustic phonons of Gamma(3) symmetry. The theoretical model describes with good accuracy the measured positions and relative intensities of the spectral lines. In addition, the mass dependence of the local gap mode of Gamma(5) symmetry reproduces the general features of the fine structures associated with the isotopic shifts of the zero-phonon line and the contribution to the isotopic shifts arising from the difference in zero-point energy between the initial and final states of the transition is evaluated.