An odmr investigation of the (Cu-li) and (cu-li)_iiicomplex defects in gap

Co-doping of GaP with Cu and Li with a two-step diffusion procedure gives rise to several neutral associates involving both Cu and Li, as revealed by bound-exciton spectra in luminescence at low temperature. In this work, odmr studies of two such associates are reported, the (Cu-Li)_Icentre with the lowest bound-exciton lines at 2.3062 eV (triplet) and 2.3072 eV (singlet), and the (Cu-Li)_IIIcentre which has four electronic bound-exciton lines in luminescence, the lowest being a triplet at 2.2419 eV. In both cases the odmr spectra show clear triplet resonances associated with the respective lowest-energy bound-exciton states. For (Cu-Li)I an orthorhombic distortion of a basically trigonal axial centre is deduced from the angular dependence of odmr data, supporting an identification of the defect as Li_j-Cu_Ga- Li, where one Li_jis bond-centred and the other is slightly distorted away from a tetrahedral interstitial site. For (Cu-Li)_IIIthe symmetry of this defect is very close to trigonal, suggesting an identification as Li_j-Cu_Ga-Cu, where the Cu essentially remains in a tetrahedral interstitial position.