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

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

Foz de Iguazú, Brasil

Conferencia; 14th International Conference on Hyperfine Interactions & 18th International Symposium on Nuclear Quadrupole Interaction; 2007

UNLP, UNCor, CBPF, USP, UFES

The combination of Hyperfine techniques and theoretical simulations based on ab initio calculations has been shown to be a powerful tool to unravel structural characterizations in the atomic scale of impurities in solids. A recent 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 111 Cd-implanted in Sn-O thin films. The samples in that case initially amorphous, seems to do not allow a precise characterization of the free-of-defect cation sites what would enable the extraction of valuable physical information from theoretical calculations such as the impurity charge state, structural relaxations, etc. In order to bridge this gap, here new - PAC experiments with 111 In-difused in polycrystalline SnO were performed to measure the EFG at ( 111 In (EC)) 111 Cd nuclei at the defect-free cation site of the SnO crystal structure. The radioactive probes were diffused into the sample during a thermal annealing from 423 K to 1000 K in seven steps in vacuum. The reversible temperature dependence of the EFG was measured afterwards in a conventional 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 by the crystal symmetry) and similar quadrupole frequencies (i.e., EFG´s) at high measuring temperatures (higher than 700 K). A strong damping of the perturbation functions was observed in the temperature range from 400 K to 600 K and the presence of dynamic hyperfine interactions is discussed. The PAC results are compared with the results coming from previous PAC experiments and with ab initio calculations already published in the literature. Also new theoretical 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 the Wien2K 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 of the 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).