Zeeman spectroscopy of crystal-field transitions of Co-doped InP

Abstract

The 474.0 meV and 785.8 meV crystal-field transitions of CoI2n+ in InP observed in photoluminescence (PL) and optical absorption respectively are studied in magnetic fields of up to 10 T. The 474.0 meV PL line is shown to arise from a Gamma 8- Gamma 8 transition in Td symmetry between the lowest spin-orbit state ( Gamma 8) of the 4T2(F) level of CoI2n+ and the spin-only Gamma 8(4A2(F)) ground state. The anisotropic g-values of the excited state, g1 and g2, are 5.48+or-0.2 and -2.98+or-0.15 respectively. An isotropic g-value of 2.14+or-0.05 is obtained for the ground state, in agreement with the results of electron spin resonance on CoI2n+. The Zeeman pattern of the 785.8 meV absorption line shows a marked trigonal (C3v) symmetry due to Jahn-Teller (JT) coupling to T2 distortion modes in the excited state. The Zeeman data are shown to be consistent with the behaviour expected from the 4A2(F) to 4T1(F) transition of CoI2n+, the 4T1(F) state undergoing an almost static JT distortion. Anticrossings in the anisotropy plot of the Zeeman pattern are observed at the main symmetry directions. This cannot be explained on a model of static C3v trigonal complexes, and is attributed to tunnelling between the magnetically equivalent distortion directions. Analysis of the Zeeman data gives gmod mod =0.96+or-0.05 and gperpendicular to =3.76+or-0.05 for the 4T1(F) excited state and g=2.10+or-0.10 for the 4A2(F) ground state.