OPTICAL AND EPR STUDY OF THE NICKEL 2-ELECTRON-TRAP STATE IN GAP

The infrared luminescence and the absorption spectra of the nickel two-electron-trap state, Ni+ 3d9, have been observed and analyzed in GaP. The spectra do not exhibit full mirror symmetry relative to the common zero-phonon line (ZPL) at 5 354 cm-1. Chemical identification of the defect is based on the fine structure of the ZPL which is shown to arise from an isotope effect. The Zeeman splitting of the ZPL in fields up to 5.3 T unambiguously demonstrates that the zero-phonon transition occurs between a cubic Γ8 excited and a Γ7 ground state, implying that the center is in the Ni+ 3d9 charge state. The analysis of the Zeeman data yields g=-0.94 for the Γ7 state and g1=1.45, qg2=-0.23 for the Γ8-state g factors. The Ni+ center was also identified in the EPR spectrum of GaP: Ni and the EPR g value is fully consistent with the Zeeman results. Certain details of the optical spectra and the strongly quenched g factors indicate a moderate Jahn-Teller (JT) coupling within the T22, and also a moderate JT coupling within the E2 state of Ni+. It is shown that static-crystal-field theory is insufficient to account for the data, and a consistent interpretation based on existing JT theories is presented. © 1979 The American Physical Society.