Study of hyperfine interactions in 111Cd-doped SnO semiconductor with PAC measurement and ab initio calculations

E. L. MUÑOZ, A. W. CARBONARI, L. A. ERRICO, H.M. PETRILLI, AND M. RENTERÍA.

Foz Do Iguazu, Brasil

Conferencia; XIV International Conference on Hyperfine Interactions & XVIII International Symposium on Nuclear Quadrupole Interaction; 2007

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The combination of Hyperfine techniques and theoretical simulations based on ab initio calculations has beenshown to be a powerful tool to unravel structural characterizations in the atomic scale of impurities in solids. Arecent example has been the study of SnO:Cd [1], where ab initio calculations questioned previous PAC assignments[2] of the electric-field gradient (EFG) at 111Cd-implanted in Sn-O thin films. The samples in that case initiallyamorphous, seems to do not allow a precise characterization of the free-of-defect cation sites what would enable theextraction of valuable physical information from theoretical calculations such as the impurity charge state, structuralrelaxations, etc. In order to bridge this gap, here new - PAC experiments with 111In-difused in polycrystallineSnO were performed to measure the EFG at ( 111In (EC)) 111Cd nuclei at the defect-free cation site of the SnOcrystal structure. The radioactive probes were diffused into the sample during a thermal annealing from 423 K to1000 K in seven steps in vacuum. The reversible temperature dependence of the EFG was measured afterwards in aconventional fast-slow coincidence PAC set-up using four conical BaF2 detectors in the range from 77 K to 1000 K.Two hyperfine interactions were observed, both with low distributions, low asymmetry parameters (as predicted bythe crystal symmetry) and similar quadrupole frequencies (i.e., EFG´s) at high measuring temperatures (higher than700 K). A strong damping of the perturbation functions was observed in the temperature range from 400 K to 600K and the presence of dynamic hyperfine interactions is discussed. The PAC results are compared with the resultscoming from previous PAC experiments and with ab initio calculations already published in the literature. Also newtheoretical calculations are performed with both the Full-Potential Linearized Augmented Plane Wave (FP-LAPW)and the Projector Augmented Wave (PAW) methods, in the framework of the Density Functional Theory, using theWien2K and CP-PAW codes, in a deeper investigation: relaxation of atomic positions, the impurity charge state, andthe determination of the impurity levels introduced in the band gap of the semiconductor are discussed in terms ofthe new experimental results.[1] L.A. Errico, M. Renter´ıa, and H.M. Petrilli, Phys.Rev. B 75, 155209 (2007).[2] M. Renter´ıa, A.G. Bibiloni, M.S. Moreno, J. Desimoni, R.C. Mercader, A. Bartos, M. Uhrmacher and K.P. Lieb,J. Phys. - Condens. Matter 3, 3625 (1991).