Quadrupole interactions of 19F implanted in germanium and gallium arsenide

Time-differential perturbed angular distribution measurements on the 197-keV isomeric state in 19F were performed using the 19F(p,p')19F* reaction to implant 19F* into hosts of Ge and GaAs. In Ge two quadrupole frequencies were detected, with νQ1=27.5 (3) MHz and νQ2=33.0 (4) MHz, while in GaAs only a single interaction was observed, with νQ=27.7 (5) MHz. In all cases the asymmetry parameter η was close to or equal to zero. The results were compared with Hartree-Fock (HF) and density-functional-theory (DFT) calculations. In the case of germanium νQ1 and νQ2 are tentatively ascribed to antibonding and bond-centered sites, respectively. In the antibonding configuration the fluorine is situated at 1.88 A along a left-angle 111 right-angle direction from a germanium atom. For F at the bond-centered site the Ge-Ge bond length was found to increase by about 1 A from its normal lattice value. In gallium arsenide the single frequency νQ is consistent with calculations for F at an intrabond site with the fluorine situated at 1.37 A from the Ga and 2.40 A from the As atom. In all cases the DFT predictions are in better agreement with experiment than those of HF