New aspects of the oxygen donor in gallium phosphide

Abstract

Newly discovered or reconsidered experimental properties of the centre are presented. Particular emphasis is given to the properties of the second electron state, OP-. The authors show that occurrence, Zeeman effect, and hole electronic excited states of an absorption transition near 1.738 eV are consistent with the D0, X BE for the centred OP0 donor, and deduce Eh*=41.7 meV, Ee=570 meV. Complex behaviours of this D0, X BE absorption in the PLE spectrum of distant DAP luminescence are fully explained. The exciton localisation energies of this BE are those of eight other donors in GaP, some nearly effective-mass-like, follow a single power-law dependence on ED. Electron capture by OP- appears to proceed via 42 meV deep excited state of centred OP-, with a further excited state 37.5 meV below the conduction band. Zeeman splittings and shifts, lifetime and phonon coupling of this transition, with no-phonon line at 528 meV, and their relation to the D0, X BE absorption and first electron capture luminescence are discussed. Evidence is presented that the absence of luminescence from the D0, X BE and the broadening of the electronic transitions results from the short lifetime of the metastable centred OP- state before relaxation to the strongly distorted rebonded ground state. Zeeman properties of the D0, X BE absorption, the distant discrete DAP no-phonon luminescence and the electron capture luminescence at OP+ are all strikingly inconsistent with a recent reassignment of the single-electron state of OP to 4T1 rather than 2A1. An alternative interpretation is advanced for the strong temperature dependence of the optical cross section sigma p10 at low T, one of the main motivations for the reassignment. The Zeeman effect of the 0.841 eV capture luminescence is quantitatively consistent with a spin doublet to spin doublet transition, rather than the transition between spin quartet states of the alternative model.